/*------------------------------------------------------------------------- * * bufmgr.c * buffer manager interface routines * * Portions Copyright (c) 1996-2013, PostgreSQL Global Development Group * Portions Copyright (c) 1994, Regents of the University of California * * * IDENTIFICATION * src/backend/storage/buffer/bufmgr.c * *------------------------------------------------------------------------- */ /* * Principal entry points: * * ReadBuffer() -- find or create a buffer holding the requested page, * and pin it so that no one can destroy it while this process * is using it. * * ReleaseBuffer() -- unpin a buffer * * MarkBufferDirty() -- mark a pinned buffer's contents as "dirty". * The disk write is delayed until buffer replacement or checkpoint. * * See also these files: * freelist.c -- chooses victim for buffer replacement * buf_table.c -- manages the buffer lookup table */ #include "postgres.h" #include #include #include "catalog/catalog.h" #include "catalog/storage.h" #include "common/relpath.h" #include "executor/instrument.h" #include "miscadmin.h" #include "pg_trace.h" #include "pgstat.h" #include "postmaster/bgwriter.h" #include "storage/buf_internals.h" #include "storage/bufmgr.h" #include "storage/ipc.h" #include "storage/proc.h" #include "storage/smgr.h" #include "storage/standby.h" #include "utils/rel.h" #include "utils/resowner_private.h" #include "utils/timestamp.h" /* Note: these two macros only work on shared buffers, not local ones! */ #define BufHdrGetBlock(bufHdr) ((Block) (BufferBlocks + ((Size) (bufHdr)->buf_id) * BLCKSZ)) #define BufferGetLSN(bufHdr) (PageGetLSN(BufHdrGetBlock(bufHdr))) /* Note: this macro only works on local buffers, not shared ones! */ #define LocalBufHdrGetBlock(bufHdr) \ LocalBufferBlockPointers[-((bufHdr)->buf_id + 2)] /* Bits in SyncOneBuffer's return value */ #define BUF_WRITTEN 0x01 #define BUF_REUSABLE 0x02 #define DROP_RELS_BSEARCH_THRESHOLD 20 /* GUC variables */ bool zero_damaged_pages = false; int bgwriter_lru_maxpages = 100; double bgwriter_lru_multiplier = 2.0; bool track_io_timing = false; /* * How many buffers PrefetchBuffer callers should try to stay ahead of their * ReadBuffer calls by. This is maintained by the assign hook for * effective_io_concurrency. Zero means "never prefetch". */ int target_prefetch_pages = 0; /* local state for StartBufferIO and related functions */ static volatile BufferDesc *InProgressBuf = NULL; static bool IsForInput; /* local state for LockBufferForCleanup */ static volatile BufferDesc *PinCountWaitBuf = NULL; static Buffer ReadBuffer_common(SMgrRelation reln, char relpersistence, ForkNumber forkNum, BlockNumber blockNum, ReadBufferMode mode, BufferAccessStrategy strategy, bool *hit); static bool PinBuffer(volatile BufferDesc *buf, BufferAccessStrategy strategy); static void PinBuffer_Locked(volatile BufferDesc *buf); static void UnpinBuffer(volatile BufferDesc *buf, bool fixOwner); static void BufferSync(int flags); static int SyncOneBuffer(int buf_id, bool skip_recently_used); static void WaitIO(volatile BufferDesc *buf); static bool StartBufferIO(volatile BufferDesc *buf, bool forInput); static void TerminateBufferIO(volatile BufferDesc *buf, bool clear_dirty, int set_flag_bits); static void shared_buffer_write_error_callback(void *arg); static void local_buffer_write_error_callback(void *arg); static volatile BufferDesc *BufferAlloc(SMgrRelation smgr, char relpersistence, ForkNumber forkNum, BlockNumber blockNum, BufferAccessStrategy strategy, bool *foundPtr); static void FlushBuffer(volatile BufferDesc *buf, SMgrRelation reln); static void AtProcExit_Buffers(int code, Datum arg); static int rnode_comparator(const void *p1, const void *p2); /* * PrefetchBuffer -- initiate asynchronous read of a block of a relation * * This is named by analogy to ReadBuffer but doesn't actually allocate a * buffer. Instead it tries to ensure that a future ReadBuffer for the given * block will not be delayed by the I/O. Prefetching is optional. * No-op if prefetching isn't compiled in. */ void PrefetchBuffer(Relation reln, ForkNumber forkNum, BlockNumber blockNum) { #ifdef USE_PREFETCH Assert(RelationIsValid(reln)); Assert(BlockNumberIsValid(blockNum)); /* Open it at the smgr level if not already done */ RelationOpenSmgr(reln); if (RelationUsesLocalBuffers(reln)) { /* see comments in ReadBufferExtended */ if (RELATION_IS_OTHER_TEMP(reln)) ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED), errmsg("cannot access temporary tables of other sessions"))); /* pass it off to localbuf.c */ LocalPrefetchBuffer(reln->rd_smgr, forkNum, blockNum); } else { BufferTag newTag; /* identity of requested block */ uint32 newHash; /* hash value for newTag */ LWLockId newPartitionLock; /* buffer partition lock for it */ int buf_id; /* create a tag so we can lookup the buffer */ INIT_BUFFERTAG(newTag, reln->rd_smgr->smgr_rnode.node, forkNum, blockNum); /* determine its hash code and partition lock ID */ newHash = BufTableHashCode(&newTag); newPartitionLock = BufMappingPartitionLock(newHash); /* see if the block is in the buffer pool already */ LWLockAcquire(newPartitionLock, LW_SHARED); buf_id = BufTableLookup(&newTag, newHash); LWLockRelease(newPartitionLock); /* If not in buffers, initiate prefetch */ if (buf_id < 0) smgrprefetch(reln->rd_smgr, forkNum, blockNum); /* * If the block *is* in buffers, we do nothing. This is not really * ideal: the block might be just about to be evicted, which would be * stupid since we know we are going to need it soon. But the only * easy answer is to bump the usage_count, which does not seem like a * great solution: when the caller does ultimately touch the block, * usage_count would get bumped again, resulting in too much * favoritism for blocks that are involved in a prefetch sequence. A * real fix would involve some additional per-buffer state, and it's * not clear that there's enough of a problem to justify that. */ } #endif /* USE_PREFETCH */ } /* * ReadBuffer -- a shorthand for ReadBufferExtended, for reading from main * fork with RBM_NORMAL mode and default strategy. */ Buffer ReadBuffer(Relation reln, BlockNumber blockNum) { return ReadBufferExtended(reln, MAIN_FORKNUM, blockNum, RBM_NORMAL, NULL); } /* * ReadBufferExtended -- returns a buffer containing the requested * block of the requested relation. If the blknum * requested is P_NEW, extend the relation file and * allocate a new block. (Caller is responsible for * ensuring that only one backend tries to extend a * relation at the same time!) * * Returns: the buffer number for the buffer containing * the block read. The returned buffer has been pinned. * Does not return on error --- elog's instead. * * Assume when this function is called, that reln has been opened already. * * In RBM_NORMAL mode, the page is read from disk, and the page header is * validated. An error is thrown if the page header is not valid. * * RBM_ZERO_ON_ERROR is like the normal mode, but if the page header is not * valid, the page is zeroed instead of throwing an error. This is intended * for non-critical data, where the caller is prepared to repair errors. * * In RBM_ZERO mode, if the page isn't in buffer cache already, it's filled * with zeros instead of reading it from disk. Useful when the caller is * going to fill the page from scratch, since this saves I/O and avoids * unnecessary failure if the page-on-disk has corrupt page headers. * Caution: do not use this mode to read a page that is beyond the relation's * current physical EOF; that is likely to cause problems in md.c when * the page is modified and written out. P_NEW is OK, though. * * If strategy is not NULL, a nondefault buffer access strategy is used. * See buffer/README for details. */ Buffer ReadBufferExtended(Relation reln, ForkNumber forkNum, BlockNumber blockNum, ReadBufferMode mode, BufferAccessStrategy strategy) { bool hit; Buffer buf; /* Open it at the smgr level if not already done */ RelationOpenSmgr(reln); /* * Reject attempts to read non-local temporary relations; we would be * likely to get wrong data since we have no visibility into the owning * session's local buffers. */ if (RELATION_IS_OTHER_TEMP(reln)) ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED), errmsg("cannot access temporary tables of other sessions"))); /* * Read the buffer, and update pgstat counters to reflect a cache hit or * miss. */ pgstat_count_buffer_read(reln); buf = ReadBuffer_common(reln->rd_smgr, reln->rd_rel->relpersistence, forkNum, blockNum, mode, strategy, &hit); if (hit) pgstat_count_buffer_hit(reln); return buf; } /* * ReadBufferWithoutRelcache -- like ReadBufferExtended, but doesn't require * a relcache entry for the relation. * * NB: At present, this function may only be used on permanent relations, which * is OK, because we only use it during XLOG replay. If in the future we * want to use it on temporary or unlogged relations, we could pass additional * parameters. */ Buffer ReadBufferWithoutRelcache(RelFileNode rnode, ForkNumber forkNum, BlockNumber blockNum, ReadBufferMode mode, BufferAccessStrategy strategy) { bool hit; SMgrRelation smgr = smgropen(rnode, InvalidBackendId); Assert(InRecovery); return ReadBuffer_common(smgr, RELPERSISTENCE_PERMANENT, forkNum, blockNum, mode, strategy, &hit); } /* * ReadBuffer_common -- common logic for all ReadBuffer variants * * *hit is set to true if the request was satisfied from shared buffer cache. */ static Buffer ReadBuffer_common(SMgrRelation smgr, char relpersistence, ForkNumber forkNum, BlockNumber blockNum, ReadBufferMode mode, BufferAccessStrategy strategy, bool *hit) { volatile BufferDesc *bufHdr; Block bufBlock; bool found; bool isExtend; bool isLocalBuf = SmgrIsTemp(smgr); *hit = false; /* Make sure we will have room to remember the buffer pin */ ResourceOwnerEnlargeBuffers(CurrentResourceOwner); isExtend = (blockNum == P_NEW); TRACE_POSTGRESQL_BUFFER_READ_START(forkNum, blockNum, smgr->smgr_rnode.node.spcNode, smgr->smgr_rnode.node.dbNode, smgr->smgr_rnode.node.relNode, smgr->smgr_rnode.backend, isExtend); /* Substitute proper block number if caller asked for P_NEW */ if (isExtend) blockNum = smgrnblocks(smgr, forkNum); if (isLocalBuf) { bufHdr = LocalBufferAlloc(smgr, forkNum, blockNum, &found); if (found) pgBufferUsage.local_blks_hit++; else pgBufferUsage.local_blks_read++; } else { /* * lookup the buffer. IO_IN_PROGRESS is set if the requested block is * not currently in memory. */ bufHdr = BufferAlloc(smgr, relpersistence, forkNum, blockNum, strategy, &found); if (found) pgBufferUsage.shared_blks_hit++; else pgBufferUsage.shared_blks_read++; } /* At this point we do NOT hold any locks. */ /* if it was already in the buffer pool, we're done */ if (found) { if (!isExtend) { /* Just need to update stats before we exit */ *hit = true; VacuumPageHit++; if (VacuumCostActive) VacuumCostBalance += VacuumCostPageHit; TRACE_POSTGRESQL_BUFFER_READ_DONE(forkNum, blockNum, smgr->smgr_rnode.node.spcNode, smgr->smgr_rnode.node.dbNode, smgr->smgr_rnode.node.relNode, smgr->smgr_rnode.backend, isExtend, found); elog (DEBUG1, "BUFMGR: Pin (reln = %i; forkNum = %i; blockNum = %i)", smgr->smgr_rnode.node.relNode, forkNum, blockNum); return BufferDescriptorGetBuffer(bufHdr); } /* * We get here only in the corner case where we are trying to extend * the relation but we found a pre-existing buffer marked BM_VALID. * This can happen because mdread doesn't complain about reads beyond * EOF (when zero_damaged_pages is ON) and so a previous attempt to * read a block beyond EOF could have left a "valid" zero-filled * buffer. Unfortunately, we have also seen this case occurring * because of buggy Linux kernels that sometimes return an * lseek(SEEK_END) result that doesn't account for a recent write. In * that situation, the pre-existing buffer would contain valid data * that we don't want to overwrite. Since the legitimate case should * always have left a zero-filled buffer, complain if not PageIsNew. */ bufBlock = isLocalBuf ? LocalBufHdrGetBlock(bufHdr) : BufHdrGetBlock(bufHdr); if (!PageIsNew((Page) bufBlock)) ereport(ERROR, (errmsg("unexpected data beyond EOF in block %u of relation %s", blockNum, relpath(smgr->smgr_rnode, forkNum)), errhint("This has been seen to occur with buggy kernels; consider updating your system."))); /* * We *must* do smgrextend before succeeding, else the page will not * be reserved by the kernel, and the next P_NEW call will decide to * return the same page. Clear the BM_VALID bit, do the StartBufferIO * call that BufferAlloc didn't, and proceed. */ if (isLocalBuf) { /* Only need to adjust flags */ Assert(bufHdr->flags & BM_VALID); bufHdr->flags &= ~BM_VALID; } else { /* * Loop to handle the very small possibility that someone re-sets * BM_VALID between our clearing it and StartBufferIO inspecting * it. */ do { LockBufHdr(bufHdr); Assert(bufHdr->flags & BM_VALID); bufHdr->flags &= ~BM_VALID; UnlockBufHdr(bufHdr); } while (!StartBufferIO(bufHdr, true)); } } /* * if we have gotten to this point, we have allocated a buffer for the * page but its contents are not yet valid. IO_IN_PROGRESS is set for it, * if it's a shared buffer. * * Note: if smgrextend fails, we will end up with a buffer that is * allocated but not marked BM_VALID. P_NEW will still select the same * block number (because the relation didn't get any longer on disk) and * so future attempts to extend the relation will find the same buffer (if * it's not been recycled) but come right back here to try smgrextend * again. */ Assert(!(bufHdr->flags & BM_VALID)); /* spinlock not needed */ bufBlock = isLocalBuf ? LocalBufHdrGetBlock(bufHdr) : BufHdrGetBlock(bufHdr); if (isExtend) { /* new buffers are zero-filled */ MemSet((char *) bufBlock, 0, BLCKSZ); /* don't set checksum for all-zero page */ smgrextend(smgr, forkNum, blockNum, (char *) bufBlock, false); } else { /* * Read in the page, unless the caller intends to overwrite it and * just wants us to allocate a buffer. */ if (mode == RBM_ZERO) MemSet((char *) bufBlock, 0, BLCKSZ); else { instr_time io_start, io_time; if (track_io_timing) INSTR_TIME_SET_CURRENT(io_start); smgrread(smgr, forkNum, blockNum, (char *) bufBlock); if (track_io_timing) { INSTR_TIME_SET_CURRENT(io_time); INSTR_TIME_SUBTRACT(io_time, io_start); pgstat_count_buffer_read_time(INSTR_TIME_GET_MICROSEC(io_time)); INSTR_TIME_ADD(pgBufferUsage.blk_read_time, io_time); } /* check for garbage data */ if (!PageIsVerified((Page) bufBlock, blockNum)) { if (mode == RBM_ZERO_ON_ERROR || zero_damaged_pages) { ereport(WARNING, (errcode(ERRCODE_DATA_CORRUPTED), errmsg("invalid page in block %u of relation %s; zeroing out page", blockNum, relpath(smgr->smgr_rnode, forkNum)))); MemSet((char *) bufBlock, 0, BLCKSZ); } else ereport(ERROR, (errcode(ERRCODE_DATA_CORRUPTED), errmsg("invalid page in block %u of relation %s", blockNum, relpath(smgr->smgr_rnode, forkNum)))); } } } if (isLocalBuf) { /* Only need to adjust flags */ bufHdr->flags |= BM_VALID; } else { /* Set BM_VALID, terminate IO, and wake up any waiters */ TerminateBufferIO(bufHdr, false, BM_VALID); } VacuumPageMiss++; if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss; TRACE_POSTGRESQL_BUFFER_READ_DONE(forkNum, blockNum, smgr->smgr_rnode.node.spcNode, smgr->smgr_rnode.node.dbNode, smgr->smgr_rnode.node.relNode, smgr->smgr_rnode.backend, isExtend, found); elog (DEBUG1, "BUFMGR: Pin (reln = %i; forkNum = %i; blockNum = %i)", smgr->smgr_rnode.node.relNode, forkNum, blockNum); return BufferDescriptorGetBuffer(bufHdr); } /* * BufferAlloc -- subroutine for ReadBuffer. Handles lookup of a shared * buffer. If no buffer exists already, selects a replacement * victim and evicts the old page, but does NOT read in new page. * * "strategy" can be a buffer replacement strategy object, or NULL for * the default strategy. The selected buffer's usage_count is advanced when * using the default strategy, but otherwise possibly not (see PinBuffer). * * The returned buffer is pinned and is already marked as holding the * desired page. If it already did have the desired page, *foundPtr is * set TRUE. Otherwise, *foundPtr is set FALSE and the buffer is marked * as IO_IN_PROGRESS; ReadBuffer will now need to do I/O to fill it. * * *foundPtr is actually redundant with the buffer's BM_VALID flag, but * we keep it for simplicity in ReadBuffer. * * No locks are held either at entry or exit. */ static volatile BufferDesc * BufferAlloc(SMgrRelation smgr, char relpersistence, ForkNumber forkNum, BlockNumber blockNum, BufferAccessStrategy strategy, bool *foundPtr) { BufferTag newTag; /* identity of requested block */ uint32 newHash; /* hash value for newTag */ LWLockId newPartitionLock; /* buffer partition lock for it */ BufferTag oldTag; /* previous identity of selected buffer */ uint32 oldHash; /* hash value for oldTag */ LWLockId oldPartitionLock; /* buffer partition lock for it */ BufFlags oldFlags; int buf_id; volatile BufferDesc *buf; bool valid; /* create a tag so we can lookup the buffer */ INIT_BUFFERTAG(newTag, smgr->smgr_rnode.node, forkNum, blockNum); /* determine its hash code and partition lock ID */ newHash = BufTableHashCode(&newTag); newPartitionLock = BufMappingPartitionLock(newHash); /* see if the block is in the buffer pool already */ LWLockAcquire(newPartitionLock, LW_SHARED); buf_id = BufTableLookup(&newTag, newHash); if (buf_id >= 0) { /* * Found it. Now, pin the buffer so no one can steal it from the * buffer pool, and check to see if the correct data has been loaded * into the buffer. */ buf = &BufferDescriptors[buf_id]; valid = PinBuffer(buf, strategy); /* Can release the mapping lock as soon as we've pinned it */ LWLockRelease(newPartitionLock); *foundPtr = TRUE; if (!valid) { /* * We can only get here if (a) someone else is still reading in * the page, or (b) a previous read attempt failed. We have to * wait for any active read attempt to finish, and then set up our * own read attempt if the page is still not BM_VALID. * StartBufferIO does it all. */ if (StartBufferIO(buf, true)) { /* * If we get here, previous attempts to read the buffer must * have failed ... but we shall bravely try again. */ *foundPtr = FALSE; } } return buf; } /* * Didn't find it in the buffer pool. We'll have to initialize a new * buffer. Remember to unlock the mapping lock while doing the work. */ LWLockRelease(newPartitionLock); /* Loop here in case we have to try another victim buffer */ for (;;) { bool lock_held; /* * Select a victim buffer. The buffer is returned with its header * spinlock still held! Also (in most cases) the BufFreelistLock is * still held, since it would be bad to hold the spinlock while * possibly waking up other processes. */ buf = StrategyGetBuffer(strategy, &lock_held); Assert(buf->refcount == 0); /* Must copy buffer flags while we still hold the spinlock */ oldFlags = buf->flags; /* Pin the buffer and then release the buffer spinlock */ PinBuffer_Locked(buf); /* Now it's safe to release the freelist lock */ if (lock_held) LWLockRelease(BufFreelistLock); /* * If the buffer was dirty, try to write it out. There is a race * condition here, in that someone might dirty it after we released it * above, or even while we are writing it out (since our share-lock * won't prevent hint-bit updates). We will recheck the dirty bit * after re-locking the buffer header. */ if (oldFlags & BM_DIRTY) { /* * We need a share-lock on the buffer contents to write it out * (else we might write invalid data, eg because someone else is * compacting the page contents while we write). We must use a * conditional lock acquisition here to avoid deadlock. Even * though the buffer was not pinned (and therefore surely not * locked) when StrategyGetBuffer returned it, someone else could * have pinned and exclusive-locked it by the time we get here. If * we try to get the lock unconditionally, we'd block waiting for * them; if they later block waiting for us, deadlock ensues. * (This has been observed to happen when two backends are both * trying to split btree index pages, and the second one just * happens to be trying to split the page the first one got from * StrategyGetBuffer.) */ if (LWLockConditionalAcquire(buf->content_lock, LW_SHARED)) { /* * If using a nondefault strategy, and writing the buffer * would require a WAL flush, let the strategy decide whether * to go ahead and write/reuse the buffer or to choose another * victim. We need lock to inspect the page LSN, so this * can't be done inside StrategyGetBuffer. */ if (strategy != NULL) { XLogRecPtr lsn; /* Read the LSN while holding buffer header lock */ LockBufHdr(buf); lsn = BufferGetLSN(buf); UnlockBufHdr(buf); if (XLogNeedsFlush(lsn) && StrategyRejectBuffer(strategy, buf)) { /* Drop lock/pin and loop around for another buffer */ LWLockRelease(buf->content_lock); UnpinBuffer(buf, true); continue; } } /* OK, do the I/O */ TRACE_POSTGRESQL_BUFFER_WRITE_DIRTY_START(forkNum, blockNum, smgr->smgr_rnode.node.spcNode, smgr->smgr_rnode.node.dbNode, smgr->smgr_rnode.node.relNode); FlushBuffer(buf, NULL); LWLockRelease(buf->content_lock); TRACE_POSTGRESQL_BUFFER_WRITE_DIRTY_DONE(forkNum, blockNum, smgr->smgr_rnode.node.spcNode, smgr->smgr_rnode.node.dbNode, smgr->smgr_rnode.node.relNode); } else { /* * Someone else has locked the buffer, so give it up and loop * back to get another one. */ UnpinBuffer(buf, true); continue; } } /* * To change the association of a valid buffer, we'll need to have * exclusive lock on both the old and new mapping partitions. */ if (oldFlags & BM_TAG_VALID) { /* * Need to compute the old tag's hashcode and partition lock ID. * XXX is it worth storing the hashcode in BufferDesc so we need * not recompute it here? Probably not. */ oldTag = buf->tag; oldHash = BufTableHashCode(&oldTag); oldPartitionLock = BufMappingPartitionLock(oldHash); /* * Must lock the lower-numbered partition first to avoid * deadlocks. */ if (oldPartitionLock < newPartitionLock) { LWLockAcquire(oldPartitionLock, LW_EXCLUSIVE); LWLockAcquire(newPartitionLock, LW_EXCLUSIVE); } else if (oldPartitionLock > newPartitionLock) { LWLockAcquire(newPartitionLock, LW_EXCLUSIVE); LWLockAcquire(oldPartitionLock, LW_EXCLUSIVE); } else { /* only one partition, only one lock */ LWLockAcquire(newPartitionLock, LW_EXCLUSIVE); } } else { /* if it wasn't valid, we need only the new partition */ LWLockAcquire(newPartitionLock, LW_EXCLUSIVE); /* these just keep the compiler quiet about uninit variables */ oldHash = 0; oldPartitionLock = 0; } /* * Try to make a hashtable entry for the buffer under its new tag. * This could fail because while we were writing someone else * allocated another buffer for the same block we want to read in. * Note that we have not yet removed the hashtable entry for the old * tag. */ buf_id = BufTableInsert(&newTag, newHash, buf->buf_id); if (buf_id >= 0) { /* * Got a collision. Someone has already done what we were about to * do. We'll just handle this as if it were found in the buffer * pool in the first place. First, give up the buffer we were * planning to use. */ UnpinBuffer(buf, true); /* Can give up that buffer's mapping partition lock now */ if ((oldFlags & BM_TAG_VALID) && oldPartitionLock != newPartitionLock) LWLockRelease(oldPartitionLock); /* remaining code should match code at top of routine */ buf = &BufferDescriptors[buf_id]; valid = PinBuffer(buf, strategy); /* Can release the mapping lock as soon as we've pinned it */ LWLockRelease(newPartitionLock); *foundPtr = TRUE; if (!valid) { /* * We can only get here if (a) someone else is still reading * in the page, or (b) a previous read attempt failed. We * have to wait for any active read attempt to finish, and * then set up our own read attempt if the page is still not * BM_VALID. StartBufferIO does it all. */ if (StartBufferIO(buf, true)) { /* * If we get here, previous attempts to read the buffer * must have failed ... but we shall bravely try again. */ *foundPtr = FALSE; } } return buf; } /* * Need to lock the buffer header too in order to change its tag. */ LockBufHdr(buf); /* * Somebody could have pinned or re-dirtied the buffer while we were * doing the I/O and making the new hashtable entry. If so, we can't * recycle this buffer; we must undo everything we've done and start * over with a new victim buffer. */ oldFlags = buf->flags; if (buf->refcount == 1 && !(oldFlags & BM_DIRTY)) break; UnlockBufHdr(buf); BufTableDelete(&newTag, newHash); if ((oldFlags & BM_TAG_VALID) && oldPartitionLock != newPartitionLock) LWLockRelease(oldPartitionLock); LWLockRelease(newPartitionLock); UnpinBuffer(buf, true); } /* * Okay, it's finally safe to rename the buffer. * * Clearing BM_VALID here is necessary, clearing the dirtybits is just * paranoia. We also reset the usage_count since any recency of use of * the old content is no longer relevant. (The usage_count starts out at * 1 so that the buffer can survive one clock-sweep pass.) */ buf->tag = newTag; buf->flags &= ~(BM_VALID | BM_DIRTY | BM_JUST_DIRTIED | BM_CHECKPOINT_NEEDED | BM_IO_ERROR | BM_PERMANENT); if (relpersistence == RELPERSISTENCE_PERMANENT) buf->flags |= BM_TAG_VALID | BM_PERMANENT; else buf->flags |= BM_TAG_VALID; buf->usage_count = 1; UnlockBufHdr(buf); if (oldFlags & BM_TAG_VALID) { BufTableDelete(&oldTag, oldHash); if (oldPartitionLock != newPartitionLock) LWLockRelease(oldPartitionLock); } LWLockRelease(newPartitionLock); /* * Buffer contents are currently invalid. Try to get the io_in_progress * lock. If StartBufferIO returns false, then someone else managed to * read it before we did, so there's nothing left for BufferAlloc() to do. */ if (StartBufferIO(buf, true)) *foundPtr = FALSE; else *foundPtr = TRUE; return buf; } /* * InvalidateBuffer -- mark a shared buffer invalid and return it to the * freelist. * * The buffer header spinlock must be held at entry. We drop it before * returning. (This is sane because the caller must have locked the * buffer in order to be sure it should be dropped.) * * This is used only in contexts such as dropping a relation. We assume * that no other backend could possibly be interested in using the page, * so the only reason the buffer might be pinned is if someone else is * trying to write it out. We have to let them finish before we can * reclaim the buffer. * * The buffer could get reclaimed by someone else while we are waiting * to acquire the necessary locks; if so, don't mess it up. */ static void InvalidateBuffer(volatile BufferDesc *buf) { BufferTag oldTag; uint32 oldHash; /* hash value for oldTag */ LWLockId oldPartitionLock; /* buffer partition lock for it */ BufFlags oldFlags; /* Save the original buffer tag before dropping the spinlock */ oldTag = buf->tag; UnlockBufHdr(buf); /* * Need to compute the old tag's hashcode and partition lock ID. XXX is it * worth storing the hashcode in BufferDesc so we need not recompute it * here? Probably not. */ oldHash = BufTableHashCode(&oldTag); oldPartitionLock = BufMappingPartitionLock(oldHash); retry: /* * Acquire exclusive mapping lock in preparation for changing the buffer's * association. */ LWLockAcquire(oldPartitionLock, LW_EXCLUSIVE); /* Re-lock the buffer header */ LockBufHdr(buf); /* If it's changed while we were waiting for lock, do nothing */ if (!BUFFERTAGS_EQUAL(buf->tag, oldTag)) { UnlockBufHdr(buf); LWLockRelease(oldPartitionLock); return; } /* * We assume the only reason for it to be pinned is that someone else is * flushing the page out. Wait for them to finish. (This could be an * infinite loop if the refcount is messed up... it would be nice to time * out after awhile, but there seems no way to be sure how many loops may * be needed. Note that if the other guy has pinned the buffer but not * yet done StartBufferIO, WaitIO will fall through and we'll effectively * be busy-looping here.) */ if (buf->refcount != 0) { UnlockBufHdr(buf); LWLockRelease(oldPartitionLock); /* safety check: should definitely not be our *own* pin */ if (PrivateRefCount[buf->buf_id] != 0) elog(ERROR, "buffer is pinned in InvalidateBuffer"); WaitIO(buf); goto retry; } /* * Clear out the buffer's tag and flags. We must do this to ensure that * linear scans of the buffer array don't think the buffer is valid. */ oldFlags = buf->flags; CLEAR_BUFFERTAG(buf->tag); buf->flags = 0; buf->usage_count = 0; UnlockBufHdr(buf); /* * Remove the buffer from the lookup hashtable, if it was in there. */ if (oldFlags & BM_TAG_VALID) BufTableDelete(&oldTag, oldHash); /* * Done with mapping lock. */ LWLockRelease(oldPartitionLock); /* * Insert the buffer at the head of the list of free buffers. */ StrategyFreeBuffer(buf); } /* * MarkBufferDirty * * Marks buffer contents as dirty (actual write happens later). * * Buffer must be pinned and exclusive-locked. (If caller does not hold * exclusive lock, then somebody could be in process of writing the buffer, * leading to risk of bad data written to disk.) */ void MarkBufferDirty(Buffer buffer) { volatile BufferDesc *bufHdr; if (!BufferIsValid(buffer)) elog(ERROR, "bad buffer ID: %d", buffer); if (BufferIsLocal(buffer)) { MarkLocalBufferDirty(buffer); return; } bufHdr = &BufferDescriptors[buffer - 1]; Assert(PrivateRefCount[buffer - 1] > 0); /* unfortunately we can't check if the lock is held exclusively */ Assert(LWLockHeldByMe(bufHdr->content_lock)); LockBufHdr(bufHdr); Assert(bufHdr->refcount > 0); /* * If the buffer was not dirty already, do vacuum accounting. */ if (!(bufHdr->flags & BM_DIRTY)) { VacuumPageDirty++; pgBufferUsage.shared_blks_dirtied++; if (VacuumCostActive) VacuumCostBalance += VacuumCostPageDirty; } bufHdr->flags |= (BM_DIRTY | BM_JUST_DIRTIED); UnlockBufHdr(bufHdr); } /* * ReleaseAndReadBuffer -- combine ReleaseBuffer() and ReadBuffer() * * Formerly, this saved one cycle of acquiring/releasing the BufMgrLock * compared to calling the two routines separately. Now it's mainly just * a convenience function. However, if the passed buffer is valid and * already contains the desired block, we just return it as-is; and that * does save considerable work compared to a full release and reacquire. * * Note: it is OK to pass buffer == InvalidBuffer, indicating that no old * buffer actually needs to be released. This case is the same as ReadBuffer, * but can save some tests in the caller. */ Buffer ReleaseAndReadBuffer(Buffer buffer, Relation relation, BlockNumber blockNum) { ForkNumber forkNum = MAIN_FORKNUM; volatile BufferDesc *bufHdr; if (BufferIsValid(buffer)) { if (BufferIsLocal(buffer)) { Assert(LocalRefCount[-buffer - 1] > 0); bufHdr = &LocalBufferDescriptors[-buffer - 1]; if (bufHdr->tag.blockNum == blockNum && RelFileNodeEquals(bufHdr->tag.rnode, relation->rd_node) && bufHdr->tag.forkNum == forkNum) return buffer; ResourceOwnerForgetBuffer(CurrentResourceOwner, buffer); LocalRefCount[-buffer - 1]--; } else { Assert(PrivateRefCount[buffer - 1] > 0); bufHdr = &BufferDescriptors[buffer - 1]; /* we have pin, so it's ok to examine tag without spinlock */ if (bufHdr->tag.blockNum == blockNum && RelFileNodeEquals(bufHdr->tag.rnode, relation->rd_node) && bufHdr->tag.forkNum == forkNum) return buffer; UnpinBuffer(bufHdr, true); } elog (DEBUG1, "BUFMGR: Unpin (reln = %i; forkNum = %i; blockNum = %i)", BufferDescriptors[buffer - 1].tag.rnode.relNode, BufferDescriptors[buffer - 1].tag.forkNum, BufferDescriptors[buffer - 1].tag.blockNum); } return ReadBuffer(relation, blockNum); } /* * PinBuffer -- make buffer unavailable for replacement. * * For the default access strategy, the buffer's usage_count is incremented * when we first pin it; for other strategies we just make sure the usage_count * isn't zero. (The idea of the latter is that we don't want synchronized * heap scans to inflate the count, but we need it to not be zero to discourage * other backends from stealing buffers from our ring. As long as we cycle * through the ring faster than the global clock-sweep cycles, buffers in * our ring won't be chosen as victims for replacement by other backends.) * * This should be applied only to shared buffers, never local ones. * * Note that ResourceOwnerEnlargeBuffers must have been done already. * * Returns TRUE if buffer is BM_VALID, else FALSE. This provision allows * some callers to avoid an extra spinlock cycle. */ static bool PinBuffer(volatile BufferDesc *buf, BufferAccessStrategy strategy) { int b = buf->buf_id; bool result; if (PrivateRefCount[b] == 0) { LockBufHdr(buf); buf->refcount++; if (strategy == NULL) { if (buf->usage_count < BM_MAX_USAGE_COUNT) buf->usage_count++; } else { if (buf->usage_count == 0) buf->usage_count = 1; } result = (buf->flags & BM_VALID) != 0; UnlockBufHdr(buf); } else { /* If we previously pinned the buffer, it must surely be valid */ result = true; } PrivateRefCount[b]++; Assert(PrivateRefCount[b] > 0); ResourceOwnerRememberBuffer(CurrentResourceOwner, BufferDescriptorGetBuffer(buf)); return result; } /* * PinBuffer_Locked -- as above, but caller already locked the buffer header. * The spinlock is released before return. * * Currently, no callers of this function want to modify the buffer's * usage_count at all, so there's no need for a strategy parameter. * Also we don't bother with a BM_VALID test (the caller could check that for * itself). * * Note: use of this routine is frequently mandatory, not just an optimization * to save a spin lock/unlock cycle, because we need to pin a buffer before * its state can change under us. */ static void PinBuffer_Locked(volatile BufferDesc *buf) { int b = buf->buf_id; if (PrivateRefCount[b] == 0) buf->refcount++; UnlockBufHdr(buf); PrivateRefCount[b]++; Assert(PrivateRefCount[b] > 0); ResourceOwnerRememberBuffer(CurrentResourceOwner, BufferDescriptorGetBuffer(buf)); } /* * UnpinBuffer -- make buffer available for replacement. * * This should be applied only to shared buffers, never local ones. * * Most but not all callers want CurrentResourceOwner to be adjusted. * Those that don't should pass fixOwner = FALSE. */ static void UnpinBuffer(volatile BufferDesc *buf, bool fixOwner) { int b = buf->buf_id; if (fixOwner) ResourceOwnerForgetBuffer(CurrentResourceOwner, BufferDescriptorGetBuffer(buf)); Assert(PrivateRefCount[b] > 0); PrivateRefCount[b]--; if (PrivateRefCount[b] == 0) { /* I'd better not still hold any locks on the buffer */ Assert(!LWLockHeldByMe(buf->content_lock)); Assert(!LWLockHeldByMe(buf->io_in_progress_lock)); LockBufHdr(buf); /* Decrement the shared reference count */ Assert(buf->refcount > 0); buf->refcount--; /* Support LockBufferForCleanup() */ if ((buf->flags & BM_PIN_COUNT_WAITER) && buf->refcount == 1) { /* we just released the last pin other than the waiter's */ int wait_backend_pid = buf->wait_backend_pid; buf->flags &= ~BM_PIN_COUNT_WAITER; UnlockBufHdr(buf); ProcSendSignal(wait_backend_pid); } else UnlockBufHdr(buf); } } /* * BufferSync -- Write out all dirty buffers in the pool. * * This is called at checkpoint time to write out all dirty shared buffers. * The checkpoint request flags should be passed in. If CHECKPOINT_IMMEDIATE * is set, we disable delays between writes; if CHECKPOINT_IS_SHUTDOWN is * set, we write even unlogged buffers, which are otherwise skipped. The * remaining flags currently have no effect here. */ static void BufferSync(int flags) { int buf_id; int num_to_scan; int num_to_write; int num_written; int mask = BM_DIRTY; /* Make sure we can handle the pin inside SyncOneBuffer */ ResourceOwnerEnlargeBuffers(CurrentResourceOwner); /* * Unless this is a shutdown checkpoint, we write only permanent, dirty * buffers. But at shutdown or end of recovery, we write all dirty * buffers. */ if (!((flags & CHECKPOINT_IS_SHUTDOWN) || (flags & CHECKPOINT_END_OF_RECOVERY))) mask |= BM_PERMANENT; /* * Loop over all buffers, and mark the ones that need to be written with * BM_CHECKPOINT_NEEDED. Count them as we go (num_to_write), so that we * can estimate how much work needs to be done. * * This allows us to write only those pages that were dirty when the * checkpoint began, and not those that get dirtied while it proceeds. * Whenever a page with BM_CHECKPOINT_NEEDED is written out, either by us * later in this function, or by normal backends or the bgwriter cleaning * scan, the flag is cleared. Any buffer dirtied after this point won't * have the flag set. * * Note that if we fail to write some buffer, we may leave buffers with * BM_CHECKPOINT_NEEDED still set. This is OK since any such buffer would * certainly need to be written for the next checkpoint attempt, too. */ num_to_write = 0; for (buf_id = 0; buf_id < NBuffers; buf_id++) { volatile BufferDesc *bufHdr = &BufferDescriptors[buf_id]; /* * Header spinlock is enough to examine BM_DIRTY, see comment in * SyncOneBuffer. */ LockBufHdr(bufHdr); if ((bufHdr->flags & mask) == mask) { bufHdr->flags |= BM_CHECKPOINT_NEEDED; num_to_write++; } UnlockBufHdr(bufHdr); } if (num_to_write == 0) return; /* nothing to do */ TRACE_POSTGRESQL_BUFFER_SYNC_START(NBuffers, num_to_write); /* * Loop over all buffers again, and write the ones (still) marked with * BM_CHECKPOINT_NEEDED. In this loop, we start at the clock sweep point * since we might as well dump soon-to-be-recycled buffers first. * * Note that we don't read the buffer alloc count here --- that should be * left untouched till the next BgBufferSync() call. */ buf_id = StrategySyncStart(NULL, NULL); num_to_scan = NBuffers; num_written = 0; while (num_to_scan-- > 0) { volatile BufferDesc *bufHdr = &BufferDescriptors[buf_id]; /* * We don't need to acquire the lock here, because we're only looking * at a single bit. It's possible that someone else writes the buffer * and clears the flag right after we check, but that doesn't matter * since SyncOneBuffer will then do nothing. However, there is a * further race condition: it's conceivable that between the time we * examine the bit here and the time SyncOneBuffer acquires lock, * someone else not only wrote the buffer but replaced it with another * page and dirtied it. In that improbable case, SyncOneBuffer will * write the buffer though we didn't need to. It doesn't seem worth * guarding against this, though. */ if (bufHdr->flags & BM_CHECKPOINT_NEEDED) { if (SyncOneBuffer(buf_id, false) & BUF_WRITTEN) { TRACE_POSTGRESQL_BUFFER_SYNC_WRITTEN(buf_id); BgWriterStats.m_buf_written_checkpoints++; num_written++; /* * We know there are at most num_to_write buffers with * BM_CHECKPOINT_NEEDED set; so we can stop scanning if * num_written reaches num_to_write. * * Note that num_written doesn't include buffers written by * other backends, or by the bgwriter cleaning scan. That * means that the estimate of how much progress we've made is * conservative, and also that this test will often fail to * trigger. But it seems worth making anyway. */ if (num_written >= num_to_write) break; /* * Sleep to throttle our I/O rate. */ CheckpointWriteDelay(flags, (double) num_written / num_to_write); } } if (++buf_id >= NBuffers) buf_id = 0; } /* * Update checkpoint statistics. As noted above, this doesn't include * buffers written by other backends or bgwriter scan. */ CheckpointStats.ckpt_bufs_written += num_written; TRACE_POSTGRESQL_BUFFER_SYNC_DONE(NBuffers, num_written, num_to_write); } /* * BgBufferSync -- Write out some dirty buffers in the pool. * * This is called periodically by the background writer process. * * Returns true if it's appropriate for the bgwriter process to go into * low-power hibernation mode. (This happens if the strategy clock sweep * has been "lapped" and no buffer allocations have occurred recently, * or if the bgwriter has been effectively disabled by setting * bgwriter_lru_maxpages to 0.) */ bool BgBufferSync(void) { /* info obtained from freelist.c */ int strategy_buf_id; uint32 strategy_passes; uint32 recent_alloc; /* * Information saved between calls so we can determine the strategy * point's advance rate and avoid scanning already-cleaned buffers. */ static bool saved_info_valid = false; static int prev_strategy_buf_id; static uint32 prev_strategy_passes; static int next_to_clean; static uint32 next_passes; /* Moving averages of allocation rate and clean-buffer density */ static float smoothed_alloc = 0; static float smoothed_density = 10.0; /* Potentially these could be tunables, but for now, not */ float smoothing_samples = 16; float scan_whole_pool_milliseconds = 120000.0; /* Used to compute how far we scan ahead */ long strategy_delta; int bufs_to_lap; int bufs_ahead; float scans_per_alloc; int reusable_buffers_est; int upcoming_alloc_est; int min_scan_buffers; /* Variables for the scanning loop proper */ int num_to_scan; int num_written; int reusable_buffers; /* Variables for final smoothed_density update */ long new_strategy_delta; uint32 new_recent_alloc; /* * Find out where the freelist clock sweep currently is, and how many * buffer allocations have happened since our last call. */ strategy_buf_id = StrategySyncStart(&strategy_passes, &recent_alloc); /* Report buffer alloc counts to pgstat */ BgWriterStats.m_buf_alloc += recent_alloc; /* * If we're not running the LRU scan, just stop after doing the stats * stuff. We mark the saved state invalid so that we can recover sanely * if LRU scan is turned back on later. */ if (bgwriter_lru_maxpages <= 0) { saved_info_valid = false; return true; } /* * Compute strategy_delta = how many buffers have been scanned by the * clock sweep since last time. If first time through, assume none. Then * see if we are still ahead of the clock sweep, and if so, how many * buffers we could scan before we'd catch up with it and "lap" it. Note: * weird-looking coding of xxx_passes comparisons are to avoid bogus * behavior when the passes counts wrap around. */ if (saved_info_valid) { int32 passes_delta = strategy_passes - prev_strategy_passes; strategy_delta = strategy_buf_id - prev_strategy_buf_id; strategy_delta += (long) passes_delta *NBuffers; Assert(strategy_delta >= 0); if ((int32) (next_passes - strategy_passes) > 0) { /* we're one pass ahead of the strategy point */ bufs_to_lap = strategy_buf_id - next_to_clean; #ifdef BGW_DEBUG elog(DEBUG2, "bgwriter ahead: bgw %u-%u strategy %u-%u delta=%ld lap=%d", next_passes, next_to_clean, strategy_passes, strategy_buf_id, strategy_delta, bufs_to_lap); #endif } else if (next_passes == strategy_passes && next_to_clean >= strategy_buf_id) { /* on same pass, but ahead or at least not behind */ bufs_to_lap = NBuffers - (next_to_clean - strategy_buf_id); #ifdef BGW_DEBUG elog(DEBUG2, "bgwriter ahead: bgw %u-%u strategy %u-%u delta=%ld lap=%d", next_passes, next_to_clean, strategy_passes, strategy_buf_id, strategy_delta, bufs_to_lap); #endif } else { /* * We're behind, so skip forward to the strategy point and start * cleaning from there. */ #ifdef BGW_DEBUG elog(DEBUG2, "bgwriter behind: bgw %u-%u strategy %u-%u delta=%ld", next_passes, next_to_clean, strategy_passes, strategy_buf_id, strategy_delta); #endif next_to_clean = strategy_buf_id; next_passes = strategy_passes; bufs_to_lap = NBuffers; } } else { /* * Initializing at startup or after LRU scanning had been off. Always * start at the strategy point. */ #ifdef BGW_DEBUG elog(DEBUG2, "bgwriter initializing: strategy %u-%u", strategy_passes, strategy_buf_id); #endif strategy_delta = 0; next_to_clean = strategy_buf_id; next_passes = strategy_passes; bufs_to_lap = NBuffers; } /* Update saved info for next time */ prev_strategy_buf_id = strategy_buf_id; prev_strategy_passes = strategy_passes; saved_info_valid = true; /* * Compute how many buffers had to be scanned for each new allocation, ie, * 1/density of reusable buffers, and track a moving average of that. * * If the strategy point didn't move, we don't update the density estimate */ if (strategy_delta > 0 && recent_alloc > 0) { scans_per_alloc = (float) strategy_delta / (float) recent_alloc; smoothed_density += (scans_per_alloc - smoothed_density) / smoothing_samples; } /* * Estimate how many reusable buffers there are between the current * strategy point and where we've scanned ahead to, based on the smoothed * density estimate. */ bufs_ahead = NBuffers - bufs_to_lap; reusable_buffers_est = (float) bufs_ahead / smoothed_density; /* * Track a moving average of recent buffer allocations. Here, rather than * a true average we want a fast-attack, slow-decline behavior: we * immediately follow any increase. */ if (smoothed_alloc <= (float) recent_alloc) smoothed_alloc = recent_alloc; else smoothed_alloc += ((float) recent_alloc - smoothed_alloc) / smoothing_samples; /* Scale the estimate by a GUC to allow more aggressive tuning. */ upcoming_alloc_est = (int) (smoothed_alloc * bgwriter_lru_multiplier); /* * If recent_alloc remains at zero for many cycles, smoothed_alloc will * eventually underflow to zero, and the underflows produce annoying * kernel warnings on some platforms. Once upcoming_alloc_est has gone to * zero, there's no point in tracking smaller and smaller values of * smoothed_alloc, so just reset it to exactly zero to avoid this * syndrome. It will pop back up as soon as recent_alloc increases. */ if (upcoming_alloc_est == 0) smoothed_alloc = 0; /* * Even in cases where there's been little or no buffer allocation * activity, we want to make a small amount of progress through the buffer * cache so that as many reusable buffers as possible are clean after an * idle period. * * (scan_whole_pool_milliseconds / BgWriterDelay) computes how many times * the BGW will be called during the scan_whole_pool time; slice the * buffer pool into that many sections. */ min_scan_buffers = (int) (NBuffers / (scan_whole_pool_milliseconds / BgWriterDelay)); if (upcoming_alloc_est < (min_scan_buffers + reusable_buffers_est)) { #ifdef BGW_DEBUG elog(DEBUG2, "bgwriter: alloc_est=%d too small, using min=%d + reusable_est=%d", upcoming_alloc_est, min_scan_buffers, reusable_buffers_est); #endif upcoming_alloc_est = min_scan_buffers + reusable_buffers_est; } /* * Now write out dirty reusable buffers, working forward from the * next_to_clean point, until we have lapped the strategy scan, or cleaned * enough buffers to match our estimate of the next cycle's allocation * requirements, or hit the bgwriter_lru_maxpages limit. */ /* Make sure we can handle the pin inside SyncOneBuffer */ ResourceOwnerEnlargeBuffers(CurrentResourceOwner); num_to_scan = bufs_to_lap; num_written = 0; reusable_buffers = reusable_buffers_est; /* Execute the LRU scan */ while (num_to_scan > 0 && reusable_buffers < upcoming_alloc_est) { int buffer_state = SyncOneBuffer(next_to_clean, true); if (++next_to_clean >= NBuffers) { next_to_clean = 0; next_passes++; } num_to_scan--; if (buffer_state & BUF_WRITTEN) { reusable_buffers++; if (++num_written >= bgwriter_lru_maxpages) { BgWriterStats.m_maxwritten_clean++; break; } } else if (buffer_state & BUF_REUSABLE) reusable_buffers++; } BgWriterStats.m_buf_written_clean += num_written; #ifdef BGW_DEBUG elog(DEBUG1, "bgwriter: recent_alloc=%u smoothed=%.2f delta=%ld ahead=%d density=%.2f reusable_est=%d upcoming_est=%d scanned=%d wrote=%d reusable=%d", recent_alloc, smoothed_alloc, strategy_delta, bufs_ahead, smoothed_density, reusable_buffers_est, upcoming_alloc_est, bufs_to_lap - num_to_scan, num_written, reusable_buffers - reusable_buffers_est); #endif /* * Consider the above scan as being like a new allocation scan. * Characterize its density and update the smoothed one based on it. This * effectively halves the moving average period in cases where both the * strategy and the background writer are doing some useful scanning, * which is helpful because a long memory isn't as desirable on the * density estimates. */ new_strategy_delta = bufs_to_lap - num_to_scan; new_recent_alloc = reusable_buffers - reusable_buffers_est; if (new_strategy_delta > 0 && new_recent_alloc > 0) { scans_per_alloc = (float) new_strategy_delta / (float) new_recent_alloc; smoothed_density += (scans_per_alloc - smoothed_density) / smoothing_samples; #ifdef BGW_DEBUG elog(DEBUG2, "bgwriter: cleaner density alloc=%u scan=%ld density=%.2f new smoothed=%.2f", new_recent_alloc, new_strategy_delta, scans_per_alloc, smoothed_density); #endif } /* Return true if OK to hibernate */ return (bufs_to_lap == 0 && recent_alloc == 0); } /* * SyncOneBuffer -- process a single buffer during syncing. * * If skip_recently_used is true, we don't write currently-pinned buffers, nor * buffers marked recently used, as these are not replacement candidates. * * Returns a bitmask containing the following flag bits: * BUF_WRITTEN: we wrote the buffer. * BUF_REUSABLE: buffer is available for replacement, ie, it has * pin count 0 and usage count 0. * * (BUF_WRITTEN could be set in error if FlushBuffers finds the buffer clean * after locking it, but we don't care all that much.) * * Note: caller must have done ResourceOwnerEnlargeBuffers. */ static int SyncOneBuffer(int buf_id, bool skip_recently_used) { volatile BufferDesc *bufHdr = &BufferDescriptors[buf_id]; int result = 0; /* * Check whether buffer needs writing. * * We can make this check without taking the buffer content lock so long * as we mark pages dirty in access methods *before* logging changes with * XLogInsert(): if someone marks the buffer dirty just after our check we * don't worry because our checkpoint.redo points before log record for * upcoming changes and so we are not required to write such dirty buffer. */ LockBufHdr(bufHdr); if (bufHdr->refcount == 0 && bufHdr->usage_count == 0) result |= BUF_REUSABLE; else if (skip_recently_used) { /* Caller told us not to write recently-used buffers */ UnlockBufHdr(bufHdr); return result; } if (!(bufHdr->flags & BM_VALID) || !(bufHdr->flags & BM_DIRTY)) { /* It's clean, so nothing to do */ UnlockBufHdr(bufHdr); return result; } /* * Pin it, share-lock it, write it. (FlushBuffer will do nothing if the * buffer is clean by the time we've locked it.) */ PinBuffer_Locked(bufHdr); LWLockAcquire(bufHdr->content_lock, LW_SHARED); FlushBuffer(bufHdr, NULL); LWLockRelease(bufHdr->content_lock); UnpinBuffer(bufHdr, true); return result | BUF_WRITTEN; } /* * AtEOXact_Buffers - clean up at end of transaction. * * As of PostgreSQL 8.0, buffer pins should get released by the * ResourceOwner mechanism. This routine is just a debugging * cross-check that no pins remain. */ void AtEOXact_Buffers(bool isCommit) { #ifdef USE_ASSERT_CHECKING if (assert_enabled) { int RefCountErrors = 0; Buffer b; for (b = 1; b <= NBuffers; b++) { if (PrivateRefCount[b - 1] != 0) { PrintBufferLeakWarning(b); RefCountErrors++; } } Assert(RefCountErrors == 0); } #endif AtEOXact_LocalBuffers(isCommit); } /* * InitBufferPoolBackend --- second-stage initialization of a new backend * * This is called after we have acquired a PGPROC and so can safely get * LWLocks. We don't currently need to do anything at this stage ... * except register a shmem-exit callback. AtProcExit_Buffers needs LWLock * access, and thereby has to be called at the corresponding phase of * backend shutdown. */ void InitBufferPoolBackend(void) { on_shmem_exit(AtProcExit_Buffers, 0); } /* * During backend exit, ensure that we released all shared-buffer locks and * assert that we have no remaining pins. */ static void AtProcExit_Buffers(int code, Datum arg) { AbortBufferIO(); UnlockBuffers(); #ifdef USE_ASSERT_CHECKING if (assert_enabled) { int RefCountErrors = 0; Buffer b; for (b = 1; b <= NBuffers; b++) { if (PrivateRefCount[b - 1] != 0) { PrintBufferLeakWarning(b); RefCountErrors++; } } Assert(RefCountErrors == 0); } #endif /* localbuf.c needs a chance too */ AtProcExit_LocalBuffers(); } /* * Helper routine to issue warnings when a buffer is unexpectedly pinned */ void PrintBufferLeakWarning(Buffer buffer) { volatile BufferDesc *buf; int32 loccount; char *path; BackendId backend; Assert(BufferIsValid(buffer)); if (BufferIsLocal(buffer)) { buf = &LocalBufferDescriptors[-buffer - 1]; loccount = LocalRefCount[-buffer - 1]; backend = MyBackendId; } else { buf = &BufferDescriptors[buffer - 1]; loccount = PrivateRefCount[buffer - 1]; backend = InvalidBackendId; } /* theoretically we should lock the bufhdr here */ path = relpathbackend(buf->tag.rnode, backend, buf->tag.forkNum); elog(WARNING, "buffer refcount leak: [%03d] " "(rel=%s, blockNum=%u, flags=0x%x, refcount=%u %d)", buffer, path, buf->tag.blockNum, buf->flags, buf->refcount, loccount); pfree(path); } /* * CheckPointBuffers * * Flush all dirty blocks in buffer pool to disk at checkpoint time. * * Note: temporary relations do not participate in checkpoints, so they don't * need to be flushed. */ void CheckPointBuffers(int flags) { TRACE_POSTGRESQL_BUFFER_CHECKPOINT_START(flags); CheckpointStats.ckpt_write_t = GetCurrentTimestamp(); BufferSync(flags); CheckpointStats.ckpt_sync_t = GetCurrentTimestamp(); TRACE_POSTGRESQL_BUFFER_CHECKPOINT_SYNC_START(); smgrsync(); CheckpointStats.ckpt_sync_end_t = GetCurrentTimestamp(); TRACE_POSTGRESQL_BUFFER_CHECKPOINT_DONE(); } /* * Do whatever is needed to prepare for commit at the bufmgr and smgr levels */ void BufmgrCommit(void) { /* Nothing to do in bufmgr anymore... */ } /* * BufferGetBlockNumber * Returns the block number associated with a buffer. * * Note: * Assumes that the buffer is valid and pinned, else the * value may be obsolete immediately... */ BlockNumber BufferGetBlockNumber(Buffer buffer) { volatile BufferDesc *bufHdr; Assert(BufferIsPinned(buffer)); if (BufferIsLocal(buffer)) bufHdr = &(LocalBufferDescriptors[-buffer - 1]); else bufHdr = &BufferDescriptors[buffer - 1]; /* pinned, so OK to read tag without spinlock */ return bufHdr->tag.blockNum; } /* * BufferGetTag * Returns the relfilenode, fork number and block number associated with * a buffer. */ void BufferGetTag(Buffer buffer, RelFileNode *rnode, ForkNumber *forknum, BlockNumber *blknum) { volatile BufferDesc *bufHdr; /* Do the same checks as BufferGetBlockNumber. */ Assert(BufferIsPinned(buffer)); if (BufferIsLocal(buffer)) bufHdr = &(LocalBufferDescriptors[-buffer - 1]); else bufHdr = &BufferDescriptors[buffer - 1]; /* pinned, so OK to read tag without spinlock */ *rnode = bufHdr->tag.rnode; *forknum = bufHdr->tag.forkNum; *blknum = bufHdr->tag.blockNum; } /* * FlushBuffer * Physically write out a shared buffer. * * NOTE: this actually just passes the buffer contents to the kernel; the * real write to disk won't happen until the kernel feels like it. This * is okay from our point of view since we can redo the changes from WAL. * However, we will need to force the changes to disk via fsync before * we can checkpoint WAL. * * The caller must hold a pin on the buffer and have share-locked the * buffer contents. (Note: a share-lock does not prevent updates of * hint bits in the buffer, so the page could change while the write * is in progress, but we assume that that will not invalidate the data * written.) * * If the caller has an smgr reference for the buffer's relation, pass it * as the second parameter. If not, pass NULL. */ static void FlushBuffer(volatile BufferDesc *buf, SMgrRelation reln) { XLogRecPtr recptr; ErrorContextCallback errcallback; instr_time io_start, io_time; Block bufBlock; char *bufToWrite; /* * Acquire the buffer's io_in_progress lock. If StartBufferIO returns * false, then someone else flushed the buffer before we could, so we need * not do anything. */ if (!StartBufferIO(buf, false)) return; /* Setup error traceback support for ereport() */ errcallback.callback = shared_buffer_write_error_callback; errcallback.arg = (void *) buf; errcallback.previous = error_context_stack; error_context_stack = &errcallback; /* Find smgr relation for buffer */ if (reln == NULL) reln = smgropen(buf->tag.rnode, InvalidBackendId); TRACE_POSTGRESQL_BUFFER_FLUSH_START(buf->tag.forkNum, buf->tag.blockNum, reln->smgr_rnode.node.spcNode, reln->smgr_rnode.node.dbNode, reln->smgr_rnode.node.relNode); LockBufHdr(buf); /* * Run PageGetLSN while holding header lock, since we don't have the * buffer locked exclusively in all cases. */ recptr = BufferGetLSN(buf); /* To check if block content changes while flushing. - vadim 01/17/97 */ buf->flags &= ~BM_JUST_DIRTIED; UnlockBufHdr(buf); /* * Force XLOG flush up to buffer's LSN. This implements the basic WAL * rule that log updates must hit disk before any of the data-file changes * they describe do. * * However, this rule does not apply to unlogged relations, which will be * lost after a crash anyway. Most unlogged relation pages do not bear * LSNs since we never emit WAL records for them, and therefore flushing * up through the buffer LSN would be useless, but harmless. However, * GiST indexes use LSNs internally to track page-splits, and therefore * unlogged GiST pages bear "fake" LSNs generated by * GetFakeLSNForUnloggedRel. It is unlikely but possible that the fake * LSN counter could advance past the WAL insertion point; and if it did * happen, attempting to flush WAL through that location would fail, with * disastrous system-wide consequences. To make sure that can't happen, * skip the flush if the buffer isn't permanent. */ if (buf->flags & BM_PERMANENT) XLogFlush(recptr); /* * Now it's safe to write buffer to disk. Note that no one else should * have been able to write it while we were busy with log flushing because * we have the io_in_progress lock. */ bufBlock = BufHdrGetBlock(buf); /* * Update page checksum if desired. Since we have only shared lock on the * buffer, other processes might be updating hint bits in it, so we must * copy the page to private storage if we do checksumming. */ bufToWrite = PageSetChecksumCopy((Page) bufBlock, buf->tag.blockNum); if (track_io_timing) INSTR_TIME_SET_CURRENT(io_start); /* * bufToWrite is either the shared buffer or a copy, as appropriate. */ smgrwrite(reln, buf->tag.forkNum, buf->tag.blockNum, bufToWrite, false); if (track_io_timing) { INSTR_TIME_SET_CURRENT(io_time); INSTR_TIME_SUBTRACT(io_time, io_start); pgstat_count_buffer_write_time(INSTR_TIME_GET_MICROSEC(io_time)); INSTR_TIME_ADD(pgBufferUsage.blk_write_time, io_time); } pgBufferUsage.shared_blks_written++; /* * Mark the buffer as clean (unless BM_JUST_DIRTIED has become set) and * end the io_in_progress state. */ TerminateBufferIO(buf, true, 0); TRACE_POSTGRESQL_BUFFER_FLUSH_DONE(buf->tag.forkNum, buf->tag.blockNum, reln->smgr_rnode.node.spcNode, reln->smgr_rnode.node.dbNode, reln->smgr_rnode.node.relNode); /* Pop the error context stack */ error_context_stack = errcallback.previous; } /* * RelationGetNumberOfBlocks * Determines the current number of pages in the relation. */ BlockNumber RelationGetNumberOfBlocksInFork(Relation relation, ForkNumber forkNum) { /* Open it at the smgr level if not already done */ RelationOpenSmgr(relation); return smgrnblocks(relation->rd_smgr, forkNum); } /* * BufferIsPermanent * Determines whether a buffer will potentially still be around after * a crash. Caller must hold a buffer pin. */ bool BufferIsPermanent(Buffer buffer) { volatile BufferDesc *bufHdr; /* Local buffers are used only for temp relations. */ if (BufferIsLocal(buffer)) return false; /* Make sure we've got a real buffer, and that we hold a pin on it. */ Assert(BufferIsValid(buffer)); Assert(BufferIsPinned(buffer)); /* * BM_PERMANENT can't be changed while we hold a pin on the buffer, so we * need not bother with the buffer header spinlock. Even if someone else * changes the buffer header flags while we're doing this, we assume that * changing an aligned 2-byte BufFlags value is atomic, so we'll read the * old value or the new value, but not random garbage. */ bufHdr = &BufferDescriptors[buffer - 1]; return (bufHdr->flags & BM_PERMANENT) != 0; } /* * BufferGetLSNAtomic * Retrieves the LSN of the buffer atomically using a buffer header lock. * This is necessary for some callers who may not have an exclusive lock * on the buffer. */ XLogRecPtr BufferGetLSNAtomic(Buffer buffer) { volatile BufferDesc *bufHdr = &BufferDescriptors[buffer - 1]; char *page = BufferGetPage(buffer); XLogRecPtr lsn; /* * If we don't need locking for correctness, fastpath out. */ if (!DataChecksumsEnabled() || BufferIsLocal(buffer)) return PageGetLSN(page); /* Make sure we've got a real buffer, and that we hold a pin on it. */ Assert(BufferIsValid(buffer)); Assert(BufferIsPinned(buffer)); LockBufHdr(bufHdr); lsn = PageGetLSN(page); UnlockBufHdr(bufHdr); return lsn; } /* --------------------------------------------------------------------- * DropRelFileNodeBuffers * * This function removes from the buffer pool all the pages of the * specified relation fork that have block numbers >= firstDelBlock. * (In particular, with firstDelBlock = 0, all pages are removed.) * Dirty pages are simply dropped, without bothering to write them * out first. Therefore, this is NOT rollback-able, and so should be * used only with extreme caution! * * Currently, this is called only from smgr.c when the underlying file * is about to be deleted or truncated (firstDelBlock is needed for * the truncation case). The data in the affected pages would therefore * be deleted momentarily anyway, and there is no point in writing it. * It is the responsibility of higher-level code to ensure that the * deletion or truncation does not lose any data that could be needed * later. It is also the responsibility of higher-level code to ensure * that no other process could be trying to load more pages of the * relation into buffers. * * XXX currently it sequentially searches the buffer pool, should be * changed to more clever ways of searching. However, this routine * is used only in code paths that aren't very performance-critical, * and we shouldn't slow down the hot paths to make it faster ... * -------------------------------------------------------------------- */ void DropRelFileNodeBuffers(RelFileNodeBackend rnode, ForkNumber forkNum, BlockNumber firstDelBlock) { int i; /* If it's a local relation, it's localbuf.c's problem. */ if (RelFileNodeBackendIsTemp(rnode)) { if (rnode.backend == MyBackendId) DropRelFileNodeLocalBuffers(rnode.node, forkNum, firstDelBlock); return; } for (i = 0; i < NBuffers; i++) { volatile BufferDesc *bufHdr = &BufferDescriptors[i]; /* * We can make this a tad faster by prechecking the buffer tag before * we attempt to lock the buffer; this saves a lot of lock * acquisitions in typical cases. It should be safe because the * caller must have AccessExclusiveLock on the relation, or some other * reason to be certain that no one is loading new pages of the rel * into the buffer pool. (Otherwise we might well miss such pages * entirely.) Therefore, while the tag might be changing while we * look at it, it can't be changing *to* a value we care about, only * *away* from such a value. So false negatives are impossible, and * false positives are safe because we'll recheck after getting the * buffer lock. * * We could check forkNum and blockNum as well as the rnode, but the * incremental win from doing so seems small. */ if (!RelFileNodeEquals(bufHdr->tag.rnode, rnode.node)) continue; LockBufHdr(bufHdr); if (RelFileNodeEquals(bufHdr->tag.rnode, rnode.node) && bufHdr->tag.forkNum == forkNum && bufHdr->tag.blockNum >= firstDelBlock) InvalidateBuffer(bufHdr); /* releases spinlock */ else UnlockBufHdr(bufHdr); } } /* --------------------------------------------------------------------- * DropRelFileNodesAllBuffers * * This function removes from the buffer pool all the pages of all * forks of the specified relations. It's equivalent to calling * DropRelFileNodeBuffers once per fork per relation with * firstDelBlock = 0. * -------------------------------------------------------------------- */ void DropRelFileNodesAllBuffers(RelFileNodeBackend *rnodes, int nnodes) { int i, n = 0; RelFileNode *nodes; bool use_bsearch; if (nnodes == 0) return; nodes = palloc(sizeof(RelFileNode) * nnodes); /* non-local relations */ /* If it's a local relation, it's localbuf.c's problem. */ for (i = 0; i < nnodes; i++) { if (RelFileNodeBackendIsTemp(rnodes[i])) { if (rnodes[i].backend == MyBackendId) DropRelFileNodeAllLocalBuffers(rnodes[i].node); } else nodes[n++] = rnodes[i].node; } /* * If there are no non-local relations, then we're done. Release the * memory and return. */ if (n == 0) { pfree(nodes); return; } /* * For low number of relations to drop just use a simple walk through, to * save the bsearch overhead. The threshold to use is rather a guess than * a exactly determined value, as it depends on many factors (CPU and RAM * speeds, amount of shared buffers etc.). */ use_bsearch = n > DROP_RELS_BSEARCH_THRESHOLD; /* sort the list of rnodes if necessary */ if (use_bsearch) pg_qsort(nodes, n, sizeof(RelFileNode), rnode_comparator); for (i = 0; i < NBuffers; i++) { RelFileNode *rnode = NULL; volatile BufferDesc *bufHdr = &BufferDescriptors[i]; /* * As in DropRelFileNodeBuffers, an unlocked precheck should be safe * and saves some cycles. */ if (!use_bsearch) { int j; for (j = 0; j < n; j++) { if (RelFileNodeEquals(bufHdr->tag.rnode, nodes[j])) { rnode = &nodes[j]; break; } } } else { rnode = bsearch((const void *) &(bufHdr->tag.rnode), nodes, n, sizeof(RelFileNode), rnode_comparator); } /* buffer doesn't belong to any of the given relfilenodes; skip it */ if (rnode == NULL) continue; LockBufHdr(bufHdr); if (RelFileNodeEquals(bufHdr->tag.rnode, (*rnode))) InvalidateBuffer(bufHdr); /* releases spinlock */ else UnlockBufHdr(bufHdr); } pfree(nodes); } /* --------------------------------------------------------------------- * DropDatabaseBuffers * * This function removes all the buffers in the buffer cache for a * particular database. Dirty pages are simply dropped, without * bothering to write them out first. This is used when we destroy a * database, to avoid trying to flush data to disk when the directory * tree no longer exists. Implementation is pretty similar to * DropRelFileNodeBuffers() which is for destroying just one relation. * -------------------------------------------------------------------- */ void DropDatabaseBuffers(Oid dbid) { int i; /* * We needn't consider local buffers, since by assumption the target * database isn't our own. */ for (i = 0; i < NBuffers; i++) { volatile BufferDesc *bufHdr = &BufferDescriptors[i]; /* * As in DropRelFileNodeBuffers, an unlocked precheck should be safe * and saves some cycles. */ if (bufHdr->tag.rnode.dbNode != dbid) continue; LockBufHdr(bufHdr); if (bufHdr->tag.rnode.dbNode == dbid) InvalidateBuffer(bufHdr); /* releases spinlock */ else UnlockBufHdr(bufHdr); } } /* ----------------------------------------------------------------- * PrintBufferDescs * * this function prints all the buffer descriptors, for debugging * use only. * ----------------------------------------------------------------- */ #ifdef NOT_USED void PrintBufferDescs(void) { int i; volatile BufferDesc *buf = BufferDescriptors; for (i = 0; i < NBuffers; ++i, ++buf) { /* theoretically we should lock the bufhdr here */ elog(LOG, "[%02d] (freeNext=%d, rel=%s, " "blockNum=%u, flags=0x%x, refcount=%u %d)", i, buf->freeNext, relpathbackend(buf->tag.rnode, InvalidBackendId, buf->tag.forkNum), buf->tag.blockNum, buf->flags, buf->refcount, PrivateRefCount[i]); } } #endif #ifdef NOT_USED void PrintPinnedBufs(void) { int i; volatile BufferDesc *buf = BufferDescriptors; for (i = 0; i < NBuffers; ++i, ++buf) { if (PrivateRefCount[i] > 0) { /* theoretically we should lock the bufhdr here */ elog(LOG, "[%02d] (freeNext=%d, rel=%s, " "blockNum=%u, flags=0x%x, refcount=%u %d)", i, buf->freeNext, relpath(buf->tag.rnode, buf->tag.forkNum), buf->tag.blockNum, buf->flags, buf->refcount, PrivateRefCount[i]); } } } #endif /* --------------------------------------------------------------------- * FlushRelationBuffers * * This function writes all dirty pages of a relation out to disk * (or more accurately, out to kernel disk buffers), ensuring that the * kernel has an up-to-date view of the relation. * * Generally, the caller should be holding AccessExclusiveLock on the * target relation to ensure that no other backend is busy dirtying * more blocks of the relation; the effects can't be expected to last * after the lock is released. * * XXX currently it sequentially searches the buffer pool, should be * changed to more clever ways of searching. This routine is not * used in any performance-critical code paths, so it's not worth * adding additional overhead to normal paths to make it go faster; * but see also DropRelFileNodeBuffers. * -------------------------------------------------------------------- */ void FlushRelationBuffers(Relation rel) { int i; volatile BufferDesc *bufHdr; /* Open rel at the smgr level if not already done */ RelationOpenSmgr(rel); if (RelationUsesLocalBuffers(rel)) { for (i = 0; i < NLocBuffer; i++) { bufHdr = &LocalBufferDescriptors[i]; if (RelFileNodeEquals(bufHdr->tag.rnode, rel->rd_node) && (bufHdr->flags & BM_VALID) && (bufHdr->flags & BM_DIRTY)) { ErrorContextCallback errcallback; Page localpage; localpage = (char *) LocalBufHdrGetBlock(bufHdr); /* Setup error traceback support for ereport() */ errcallback.callback = local_buffer_write_error_callback; errcallback.arg = (void *) bufHdr; errcallback.previous = error_context_stack; error_context_stack = &errcallback; PageSetChecksumInplace(localpage, bufHdr->tag.blockNum); smgrwrite(rel->rd_smgr, bufHdr->tag.forkNum, bufHdr->tag.blockNum, localpage, false); bufHdr->flags &= ~(BM_DIRTY | BM_JUST_DIRTIED); /* Pop the error context stack */ error_context_stack = errcallback.previous; } } return; } /* Make sure we can handle the pin inside the loop */ ResourceOwnerEnlargeBuffers(CurrentResourceOwner); for (i = 0; i < NBuffers; i++) { bufHdr = &BufferDescriptors[i]; /* * As in DropRelFileNodeBuffers, an unlocked precheck should be safe * and saves some cycles. */ if (!RelFileNodeEquals(bufHdr->tag.rnode, rel->rd_node)) continue; LockBufHdr(bufHdr); if (RelFileNodeEquals(bufHdr->tag.rnode, rel->rd_node) && (bufHdr->flags & BM_VALID) && (bufHdr->flags & BM_DIRTY)) { PinBuffer_Locked(bufHdr); LWLockAcquire(bufHdr->content_lock, LW_SHARED); FlushBuffer(bufHdr, rel->rd_smgr); LWLockRelease(bufHdr->content_lock); UnpinBuffer(bufHdr, true); } else UnlockBufHdr(bufHdr); } } /* --------------------------------------------------------------------- * FlushDatabaseBuffers * * This function writes all dirty pages of a database out to disk * (or more accurately, out to kernel disk buffers), ensuring that the * kernel has an up-to-date view of the database. * * Generally, the caller should be holding an appropriate lock to ensure * no other backend is active in the target database; otherwise more * pages could get dirtied. * * Note we don't worry about flushing any pages of temporary relations. * It's assumed these wouldn't be interesting. * -------------------------------------------------------------------- */ void FlushDatabaseBuffers(Oid dbid) { int i; volatile BufferDesc *bufHdr; /* Make sure we can handle the pin inside the loop */ ResourceOwnerEnlargeBuffers(CurrentResourceOwner); for (i = 0; i < NBuffers; i++) { bufHdr = &BufferDescriptors[i]; /* * As in DropRelFileNodeBuffers, an unlocked precheck should be safe * and saves some cycles. */ if (bufHdr->tag.rnode.dbNode != dbid) continue; LockBufHdr(bufHdr); if (bufHdr->tag.rnode.dbNode == dbid && (bufHdr->flags & BM_VALID) && (bufHdr->flags & BM_DIRTY)) { PinBuffer_Locked(bufHdr); LWLockAcquire(bufHdr->content_lock, LW_SHARED); FlushBuffer(bufHdr, NULL); LWLockRelease(bufHdr->content_lock); UnpinBuffer(bufHdr, true); } else UnlockBufHdr(bufHdr); } } /* * ReleaseBuffer -- release the pin on a buffer */ void ReleaseBuffer(Buffer buffer) { volatile BufferDesc *bufHdr; if (!BufferIsValid(buffer)) elog(ERROR, "bad buffer ID: %d", buffer); elog (DEBUG1, "BUFMGR: Unpin (reln = %i; forkNum = %i; blockNum = %i)", BufferDescriptors[buffer - 1].tag.rnode.relNode, BufferDescriptors[buffer - 1].tag.forkNum, BufferDescriptors[buffer - 1].tag.blockNum); ResourceOwnerForgetBuffer(CurrentResourceOwner, buffer); if (BufferIsLocal(buffer)) { Assert(LocalRefCount[-buffer - 1] > 0); LocalRefCount[-buffer - 1]--; return; } bufHdr = &BufferDescriptors[buffer - 1]; Assert(PrivateRefCount[buffer - 1] > 0); if (PrivateRefCount[buffer - 1] > 1) PrivateRefCount[buffer - 1]--; else UnpinBuffer(bufHdr, false); } /* * UnlockReleaseBuffer -- release the content lock and pin on a buffer * * This is just a shorthand for a common combination. */ void UnlockReleaseBuffer(Buffer buffer) { LockBuffer(buffer, BUFFER_LOCK_UNLOCK); ReleaseBuffer(buffer); } /* * IncrBufferRefCount * Increment the pin count on a buffer that we have *already* pinned * at least once. * * This function cannot be used on a buffer we do not have pinned, * because it doesn't change the shared buffer state. */ void IncrBufferRefCount(Buffer buffer) { Assert(BufferIsPinned(buffer)); ResourceOwnerEnlargeBuffers(CurrentResourceOwner); ResourceOwnerRememberBuffer(CurrentResourceOwner, buffer); if (BufferIsLocal(buffer)) LocalRefCount[-buffer - 1]++; else PrivateRefCount[buffer - 1]++; elog (DEBUG1, "BUFMGR: Pin (reln = %i; forkNum = %i; blockNum = %i)", BufferDescriptors[buffer - 1].tag.rnode.relNode, BufferDescriptors[buffer - 1].tag.forkNum, BufferDescriptors[buffer - 1].tag.blockNum); } /* * MarkBufferDirtyHint * * Mark a buffer dirty for non-critical changes. * * This is essentially the same as MarkBufferDirty, except: * * 1. The caller does not write WAL; so if checksums are enabled, we may need * to write an XLOG_HINT WAL record to protect against torn pages. * 2. The caller might have only share-lock instead of exclusive-lock on the * buffer's content lock. * 3. This function does not guarantee that the buffer is always marked dirty * (due to a race condition), so it cannot be used for important changes. */ void MarkBufferDirtyHint(Buffer buffer, bool buffer_std) { volatile BufferDesc *bufHdr; Page page = BufferGetPage(buffer); if (!BufferIsValid(buffer)) elog(ERROR, "bad buffer ID: %d", buffer); if (BufferIsLocal(buffer)) { MarkLocalBufferDirty(buffer); return; } bufHdr = &BufferDescriptors[buffer - 1]; Assert(PrivateRefCount[buffer - 1] > 0); /* here, either share or exclusive lock is OK */ Assert(LWLockHeldByMe(bufHdr->content_lock)); /* * This routine might get called many times on the same page, if we are * making the first scan after commit of an xact that added/deleted many * tuples. So, be as quick as we can if the buffer is already dirty. We * do this by not acquiring spinlock if it looks like the status bits are * already set. Since we make this test unlocked, there's a chance we * might fail to notice that the flags have just been cleared, and failed * to reset them, due to memory-ordering issues. But since this function * is only intended to be used in cases where failing to write out the * data would be harmless anyway, it doesn't really matter. */ if ((bufHdr->flags & (BM_DIRTY | BM_JUST_DIRTIED)) != (BM_DIRTY | BM_JUST_DIRTIED)) { XLogRecPtr lsn = InvalidXLogRecPtr; bool dirtied = false; bool delayChkpt = false; /* * If checksums are enabled, and the buffer is permanent, then a full * page image may be required even for some hint bit updates to * protect against torn pages. This full page image is only necessary * if the hint bit update is the first change to the page since the * last checkpoint. * * We don't check full_page_writes here because that logic is included * when we call XLogInsert() since the value changes dynamically. */ if (DataChecksumsEnabled() && (bufHdr->flags & BM_PERMANENT)) { /* * If we're in recovery we cannot dirty a page because of a hint. * We can set the hint, just not dirty the page as a result so the * hint is lost when we evict the page or shutdown. * * See src/backend/storage/page/README for longer discussion. */ if (RecoveryInProgress()) return; /* * If the block is already dirty because we either made a change * or set a hint already, then we don't need to write a full page * image. Note that aggressive cleaning of blocks dirtied by hint * bit setting would increase the call rate. Bulk setting of hint * bits would reduce the call rate... * * We must issue the WAL record before we mark the buffer dirty. * Otherwise we might write the page before we write the WAL. That * causes a race condition, since a checkpoint might occur between * writing the WAL record and marking the buffer dirty. We solve * that with a kluge, but one that is already in use during * transaction commit to prevent race conditions. Basically, we * simply prevent the checkpoint WAL record from being written * until we have marked the buffer dirty. We don't start the * checkpoint flush until we have marked dirty, so our checkpoint * must flush the change to disk successfully or the checkpoint * never gets written, so crash recovery will fix. * * It's possible we may enter here without an xid, so it is * essential that CreateCheckpoint waits for virtual transactions * rather than full transactionids. */ MyPgXact->delayChkpt = delayChkpt = true; lsn = XLogSaveBufferForHint(buffer, buffer_std); } LockBufHdr(bufHdr); Assert(bufHdr->refcount > 0); if (!(bufHdr->flags & BM_DIRTY)) { dirtied = true; /* Means "will be dirtied by this action" */ /* * Set the page LSN if we wrote a backup block. We aren't supposed * to set this when only holding a share lock but as long as we * serialise it somehow we're OK. We choose to set LSN while * holding the buffer header lock, which causes any reader of an * LSN who holds only a share lock to also obtain a buffer header * lock before using PageGetLSN(), which is enforced in * BufferGetLSNAtomic(). * * If checksums are enabled, you might think we should reset the * checksum here. That will happen when the page is written * sometime later in this checkpoint cycle. */ if (!XLogRecPtrIsInvalid(lsn)) PageSetLSN(page, lsn); } bufHdr->flags |= (BM_DIRTY | BM_JUST_DIRTIED); UnlockBufHdr(bufHdr); if (delayChkpt) MyPgXact->delayChkpt = false; if (dirtied) { VacuumPageDirty++; if (VacuumCostActive) VacuumCostBalance += VacuumCostPageDirty; } } } /* * Release buffer content locks for shared buffers. * * Used to clean up after errors. * * Currently, we can expect that lwlock.c's LWLockReleaseAll() took care * of releasing buffer content locks per se; the only thing we need to deal * with here is clearing any PIN_COUNT request that was in progress. */ void UnlockBuffers(void) { volatile BufferDesc *buf = PinCountWaitBuf; if (buf) { LockBufHdr(buf); /* * Don't complain if flag bit not set; it could have been reset but we * got a cancel/die interrupt before getting the signal. */ if ((buf->flags & BM_PIN_COUNT_WAITER) != 0 && buf->wait_backend_pid == MyProcPid) buf->flags &= ~BM_PIN_COUNT_WAITER; UnlockBufHdr(buf); PinCountWaitBuf = NULL; } } /* * Acquire or release the content_lock for the buffer. */ void LockBuffer(Buffer buffer, int mode) { volatile BufferDesc *buf; Assert(BufferIsValid(buffer)); if (BufferIsLocal(buffer)) return; /* local buffers need no lock */ buf = &(BufferDescriptors[buffer - 1]); if (mode == BUFFER_LOCK_UNLOCK) LWLockRelease(buf->content_lock); else if (mode == BUFFER_LOCK_SHARE) LWLockAcquire(buf->content_lock, LW_SHARED); else if (mode == BUFFER_LOCK_EXCLUSIVE) LWLockAcquire(buf->content_lock, LW_EXCLUSIVE); else elog(ERROR, "unrecognized buffer lock mode: %d", mode); } /* * Acquire the content_lock for the buffer, but only if we don't have to wait. * * This assumes the caller wants BUFFER_LOCK_EXCLUSIVE mode. */ bool ConditionalLockBuffer(Buffer buffer) { volatile BufferDesc *buf; Assert(BufferIsValid(buffer)); if (BufferIsLocal(buffer)) return true; /* act as though we got it */ buf = &(BufferDescriptors[buffer - 1]); return LWLockConditionalAcquire(buf->content_lock, LW_EXCLUSIVE); } /* * LockBufferForCleanup - lock a buffer in preparation for deleting items * * Items may be deleted from a disk page only when the caller (a) holds an * exclusive lock on the buffer and (b) has observed that no other backend * holds a pin on the buffer. If there is a pin, then the other backend * might have a pointer into the buffer (for example, a heapscan reference * to an item --- see README for more details). It's OK if a pin is added * after the cleanup starts, however; the newly-arrived backend will be * unable to look at the page until we release the exclusive lock. * * To implement this protocol, a would-be deleter must pin the buffer and * then call LockBufferForCleanup(). LockBufferForCleanup() is similar to * LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE), except that it loops until * it has successfully observed pin count = 1. */ void LockBufferForCleanup(Buffer buffer) { volatile BufferDesc *bufHdr; Assert(BufferIsValid(buffer)); Assert(PinCountWaitBuf == NULL); if (BufferIsLocal(buffer)) { /* There should be exactly one pin */ if (LocalRefCount[-buffer - 1] != 1) elog(ERROR, "incorrect local pin count: %d", LocalRefCount[-buffer - 1]); /* Nobody else to wait for */ return; } /* There should be exactly one local pin */ if (PrivateRefCount[buffer - 1] != 1) elog(ERROR, "incorrect local pin count: %d", PrivateRefCount[buffer - 1]); bufHdr = &BufferDescriptors[buffer - 1]; for (;;) { /* Try to acquire lock */ LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE); LockBufHdr(bufHdr); Assert(bufHdr->refcount > 0); if (bufHdr->refcount == 1) { /* Successfully acquired exclusive lock with pincount 1 */ UnlockBufHdr(bufHdr); return; } /* Failed, so mark myself as waiting for pincount 1 */ if (bufHdr->flags & BM_PIN_COUNT_WAITER) { UnlockBufHdr(bufHdr); LockBuffer(buffer, BUFFER_LOCK_UNLOCK); elog(ERROR, "multiple backends attempting to wait for pincount 1"); } bufHdr->wait_backend_pid = MyProcPid; bufHdr->flags |= BM_PIN_COUNT_WAITER; PinCountWaitBuf = bufHdr; UnlockBufHdr(bufHdr); LockBuffer(buffer, BUFFER_LOCK_UNLOCK); /* Wait to be signaled by UnpinBuffer() */ if (InHotStandby) { /* Publish the bufid that Startup process waits on */ SetStartupBufferPinWaitBufId(buffer - 1); /* Set alarm and then wait to be signaled by UnpinBuffer() */ ResolveRecoveryConflictWithBufferPin(); /* Reset the published bufid */ SetStartupBufferPinWaitBufId(-1); } else ProcWaitForSignal(); PinCountWaitBuf = NULL; /* Loop back and try again */ } } /* * Check called from RecoveryConflictInterrupt handler when Startup * process requests cancellation of all pin holders that are blocking it. */ bool HoldingBufferPinThatDelaysRecovery(void) { int bufid = GetStartupBufferPinWaitBufId(); /* * If we get woken slowly then it's possible that the Startup process was * already woken by other backends before we got here. Also possible that * we get here by multiple interrupts or interrupts at inappropriate * times, so make sure we do nothing if the bufid is not set. */ if (bufid < 0) return false; if (PrivateRefCount[bufid] > 0) return true; return false; } /* * ConditionalLockBufferForCleanup - as above, but don't wait to get the lock * * We won't loop, but just check once to see if the pin count is OK. If * not, return FALSE with no lock held. */ bool ConditionalLockBufferForCleanup(Buffer buffer) { volatile BufferDesc *bufHdr; Assert(BufferIsValid(buffer)); if (BufferIsLocal(buffer)) { /* There should be exactly one pin */ Assert(LocalRefCount[-buffer - 1] > 0); if (LocalRefCount[-buffer - 1] != 1) return false; /* Nobody else to wait for */ return true; } /* There should be exactly one local pin */ Assert(PrivateRefCount[buffer - 1] > 0); if (PrivateRefCount[buffer - 1] != 1) return false; /* Try to acquire lock */ if (!ConditionalLockBuffer(buffer)) return false; bufHdr = &BufferDescriptors[buffer - 1]; LockBufHdr(bufHdr); Assert(bufHdr->refcount > 0); if (bufHdr->refcount == 1) { /* Successfully acquired exclusive lock with pincount 1 */ UnlockBufHdr(bufHdr); return true; } /* Failed, so release the lock */ UnlockBufHdr(bufHdr); LockBuffer(buffer, BUFFER_LOCK_UNLOCK); return false; } /* * Functions for buffer I/O handling * * Note: We assume that nested buffer I/O never occurs. * i.e at most one io_in_progress lock is held per proc. * * Also note that these are used only for shared buffers, not local ones. */ /* * WaitIO -- Block until the IO_IN_PROGRESS flag on 'buf' is cleared. */ static void WaitIO(volatile BufferDesc *buf) { /* * Changed to wait until there's no IO - Inoue 01/13/2000 * * Note this is *necessary* because an error abort in the process doing * I/O could release the io_in_progress_lock prematurely. See * AbortBufferIO. */ for (;;) { BufFlags sv_flags; /* * It may not be necessary to acquire the spinlock to check the flag * here, but since this test is essential for correctness, we'd better * play it safe. */ LockBufHdr(buf); sv_flags = buf->flags; UnlockBufHdr(buf); if (!(sv_flags & BM_IO_IN_PROGRESS)) break; LWLockAcquire(buf->io_in_progress_lock, LW_SHARED); LWLockRelease(buf->io_in_progress_lock); } } /* * StartBufferIO: begin I/O on this buffer * (Assumptions) * My process is executing no IO * The buffer is Pinned * * In some scenarios there are race conditions in which multiple backends * could attempt the same I/O operation concurrently. If someone else * has already started I/O on this buffer then we will block on the * io_in_progress lock until he's done. * * Input operations are only attempted on buffers that are not BM_VALID, * and output operations only on buffers that are BM_VALID and BM_DIRTY, * so we can always tell if the work is already done. * * Returns TRUE if we successfully marked the buffer as I/O busy, * FALSE if someone else already did the work. */ static bool StartBufferIO(volatile BufferDesc *buf, bool forInput) { Assert(!InProgressBuf); for (;;) { /* * Grab the io_in_progress lock so that other processes can wait for * me to finish the I/O. */ LWLockAcquire(buf->io_in_progress_lock, LW_EXCLUSIVE); LockBufHdr(buf); if (!(buf->flags & BM_IO_IN_PROGRESS)) break; /* * The only way BM_IO_IN_PROGRESS could be set when the io_in_progress * lock isn't held is if the process doing the I/O is recovering from * an error (see AbortBufferIO). If that's the case, we must wait for * him to get unwedged. */ UnlockBufHdr(buf); LWLockRelease(buf->io_in_progress_lock); WaitIO(buf); } /* Once we get here, there is definitely no I/O active on this buffer */ if (forInput ? (buf->flags & BM_VALID) : !(buf->flags & BM_DIRTY)) { /* someone else already did the I/O */ UnlockBufHdr(buf); LWLockRelease(buf->io_in_progress_lock); return false; } buf->flags |= BM_IO_IN_PROGRESS; UnlockBufHdr(buf); InProgressBuf = buf; IsForInput = forInput; return true; } /* * TerminateBufferIO: release a buffer we were doing I/O on * (Assumptions) * My process is executing IO for the buffer * BM_IO_IN_PROGRESS bit is set for the buffer * We hold the buffer's io_in_progress lock * The buffer is Pinned * * If clear_dirty is TRUE and BM_JUST_DIRTIED is not set, we clear the * buffer's BM_DIRTY flag. This is appropriate when terminating a * successful write. The check on BM_JUST_DIRTIED is necessary to avoid * marking the buffer clean if it was re-dirtied while we were writing. * * set_flag_bits gets ORed into the buffer's flags. It must include * BM_IO_ERROR in a failure case. For successful completion it could * be 0, or BM_VALID if we just finished reading in the page. */ static void TerminateBufferIO(volatile BufferDesc *buf, bool clear_dirty, int set_flag_bits) { Assert(buf == InProgressBuf); LockBufHdr(buf); Assert(buf->flags & BM_IO_IN_PROGRESS); buf->flags &= ~(BM_IO_IN_PROGRESS | BM_IO_ERROR); if (clear_dirty && !(buf->flags & BM_JUST_DIRTIED)) buf->flags &= ~(BM_DIRTY | BM_CHECKPOINT_NEEDED); buf->flags |= set_flag_bits; UnlockBufHdr(buf); InProgressBuf = NULL; LWLockRelease(buf->io_in_progress_lock); } /* * AbortBufferIO: Clean up any active buffer I/O after an error. * * All LWLocks we might have held have been released, * but we haven't yet released buffer pins, so the buffer is still pinned. * * If I/O was in progress, we always set BM_IO_ERROR, even though it's * possible the error condition wasn't related to the I/O. */ void AbortBufferIO(void) { volatile BufferDesc *buf = InProgressBuf; if (buf) { /* * Since LWLockReleaseAll has already been called, we're not holding * the buffer's io_in_progress_lock. We have to re-acquire it so that * we can use TerminateBufferIO. Anyone who's executing WaitIO on the * buffer will be in a busy spin until we succeed in doing this. */ LWLockAcquire(buf->io_in_progress_lock, LW_EXCLUSIVE); LockBufHdr(buf); Assert(buf->flags & BM_IO_IN_PROGRESS); if (IsForInput) { Assert(!(buf->flags & BM_DIRTY)); /* We'd better not think buffer is valid yet */ Assert(!(buf->flags & BM_VALID)); UnlockBufHdr(buf); } else { BufFlags sv_flags; sv_flags = buf->flags; Assert(sv_flags & BM_DIRTY); UnlockBufHdr(buf); /* Issue notice if this is not the first failure... */ if (sv_flags & BM_IO_ERROR) { /* Buffer is pinned, so we can read tag without spinlock */ char *path; path = relpathperm(buf->tag.rnode, buf->tag.forkNum); ereport(WARNING, (errcode(ERRCODE_IO_ERROR), errmsg("could not write block %u of %s", buf->tag.blockNum, path), errdetail("Multiple failures --- write error might be permanent."))); pfree(path); } } TerminateBufferIO(buf, false, BM_IO_ERROR); } } /* * Error context callback for errors occurring during shared buffer writes. */ static void shared_buffer_write_error_callback(void *arg) { volatile BufferDesc *bufHdr = (volatile BufferDesc *) arg; /* Buffer is pinned, so we can read the tag without locking the spinlock */ if (bufHdr != NULL) { char *path = relpathperm(bufHdr->tag.rnode, bufHdr->tag.forkNum); errcontext("writing block %u of relation %s", bufHdr->tag.blockNum, path); pfree(path); } } /* * Error context callback for errors occurring during local buffer writes. */ static void local_buffer_write_error_callback(void *arg) { volatile BufferDesc *bufHdr = (volatile BufferDesc *) arg; if (bufHdr != NULL) { char *path = relpathbackend(bufHdr->tag.rnode, MyBackendId, bufHdr->tag.forkNum); errcontext("writing block %u of relation %s", bufHdr->tag.blockNum, path); pfree(path); } } /* * RelFileNode qsort/bsearch comparator; see RelFileNodeEquals. */ static int rnode_comparator(const void *p1, const void *p2) { RelFileNode n1 = *(RelFileNode *) p1; RelFileNode n2 = *(RelFileNode *) p2; if (n1.relNode < n2.relNode) return -1; else if (n1.relNode > n2.relNode) return 1; if (n1.dbNode < n2.dbNode) return -1; else if (n1.dbNode > n2.dbNode) return 1; if (n1.spcNode < n2.spcNode) return -1; else if (n1.spcNode > n2.spcNode) return 1; else return 0; }