diff options
Diffstat (limited to 'src/backend/access/heap/hio.c')
| -rw-r--r-- | src/backend/access/heap/hio.c | 686 |
1 files changed, 686 insertions, 0 deletions
diff --git a/src/backend/access/heap/hio.c b/src/backend/access/heap/hio.c new file mode 100644 index 0000000..43a43a8 --- /dev/null +++ b/src/backend/access/heap/hio.c @@ -0,0 +1,686 @@ +/*------------------------------------------------------------------------- + * + * hio.c + * POSTGRES heap access method input/output code. + * + * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group + * Portions Copyright (c) 1994, Regents of the University of California + * + * + * IDENTIFICATION + * src/backend/access/heap/hio.c + * + *------------------------------------------------------------------------- + */ + +#include "postgres.h" + +#include "access/heapam.h" +#include "access/hio.h" +#include "access/htup_details.h" +#include "access/visibilitymap.h" +#include "storage/bufmgr.h" +#include "storage/freespace.h" +#include "storage/lmgr.h" +#include "storage/smgr.h" + + +/* + * RelationPutHeapTuple - place tuple at specified page + * + * !!! EREPORT(ERROR) IS DISALLOWED HERE !!! Must PANIC on failure!!! + * + * Note - caller must hold BUFFER_LOCK_EXCLUSIVE on the buffer. + */ +void +RelationPutHeapTuple(Relation relation, + Buffer buffer, + HeapTuple tuple, + bool token) +{ + Page pageHeader; + OffsetNumber offnum; + + /* + * A tuple that's being inserted speculatively should already have its + * token set. + */ + Assert(!token || HeapTupleHeaderIsSpeculative(tuple->t_data)); + + /* Add the tuple to the page */ + pageHeader = BufferGetPage(buffer); + + offnum = PageAddItem(pageHeader, (Item) tuple->t_data, + tuple->t_len, InvalidOffsetNumber, false, true); + + if (offnum == InvalidOffsetNumber) + elog(PANIC, "failed to add tuple to page"); + + /* Update tuple->t_self to the actual position where it was stored */ + ItemPointerSet(&(tuple->t_self), BufferGetBlockNumber(buffer), offnum); + + /* + * Insert the correct position into CTID of the stored tuple, too (unless + * this is a speculative insertion, in which case the token is held in + * CTID field instead) + */ + if (!token) + { + ItemId itemId = PageGetItemId(pageHeader, offnum); + HeapTupleHeader item = (HeapTupleHeader) PageGetItem(pageHeader, itemId); + + item->t_ctid = tuple->t_self; + } +} + +/* + * Read in a buffer in mode, using bulk-insert strategy if bistate isn't NULL. + */ +static Buffer +ReadBufferBI(Relation relation, BlockNumber targetBlock, + ReadBufferMode mode, BulkInsertState bistate) +{ + Buffer buffer; + + /* If not bulk-insert, exactly like ReadBuffer */ + if (!bistate) + return ReadBufferExtended(relation, MAIN_FORKNUM, targetBlock, + mode, NULL); + + /* If we have the desired block already pinned, re-pin and return it */ + if (bistate->current_buf != InvalidBuffer) + { + if (BufferGetBlockNumber(bistate->current_buf) == targetBlock) + { + /* + * Currently the LOCK variants are only used for extending + * relation, which should never reach this branch. + */ + Assert(mode != RBM_ZERO_AND_LOCK && + mode != RBM_ZERO_AND_CLEANUP_LOCK); + + IncrBufferRefCount(bistate->current_buf); + return bistate->current_buf; + } + /* ... else drop the old buffer */ + ReleaseBuffer(bistate->current_buf); + bistate->current_buf = InvalidBuffer; + } + + /* Perform a read using the buffer strategy */ + buffer = ReadBufferExtended(relation, MAIN_FORKNUM, targetBlock, + mode, bistate->strategy); + + /* Save the selected block as target for future inserts */ + IncrBufferRefCount(buffer); + bistate->current_buf = buffer; + + return buffer; +} + +/* + * For each heap page which is all-visible, acquire a pin on the appropriate + * visibility map page, if we haven't already got one. + * + * buffer2 may be InvalidBuffer, if only one buffer is involved. buffer1 + * must not be InvalidBuffer. If both buffers are specified, block1 must + * be less than block2. + */ +static void +GetVisibilityMapPins(Relation relation, Buffer buffer1, Buffer buffer2, + BlockNumber block1, BlockNumber block2, + Buffer *vmbuffer1, Buffer *vmbuffer2) +{ + bool need_to_pin_buffer1; + bool need_to_pin_buffer2; + + Assert(BufferIsValid(buffer1)); + Assert(buffer2 == InvalidBuffer || block1 <= block2); + + while (1) + { + /* Figure out which pins we need but don't have. */ + need_to_pin_buffer1 = PageIsAllVisible(BufferGetPage(buffer1)) + && !visibilitymap_pin_ok(block1, *vmbuffer1); + need_to_pin_buffer2 = buffer2 != InvalidBuffer + && PageIsAllVisible(BufferGetPage(buffer2)) + && !visibilitymap_pin_ok(block2, *vmbuffer2); + if (!need_to_pin_buffer1 && !need_to_pin_buffer2) + return; + + /* We must unlock both buffers before doing any I/O. */ + LockBuffer(buffer1, BUFFER_LOCK_UNLOCK); + if (buffer2 != InvalidBuffer && buffer2 != buffer1) + LockBuffer(buffer2, BUFFER_LOCK_UNLOCK); + + /* Get pins. */ + if (need_to_pin_buffer1) + visibilitymap_pin(relation, block1, vmbuffer1); + if (need_to_pin_buffer2) + visibilitymap_pin(relation, block2, vmbuffer2); + + /* Relock buffers. */ + LockBuffer(buffer1, BUFFER_LOCK_EXCLUSIVE); + if (buffer2 != InvalidBuffer && buffer2 != buffer1) + LockBuffer(buffer2, BUFFER_LOCK_EXCLUSIVE); + + /* + * If there are two buffers involved and we pinned just one of them, + * it's possible that the second one became all-visible while we were + * busy pinning the first one. If it looks like that's a possible + * scenario, we'll need to make a second pass through this loop. + */ + if (buffer2 == InvalidBuffer || buffer1 == buffer2 + || (need_to_pin_buffer1 && need_to_pin_buffer2)) + break; + } +} + +/* + * Extend a relation by multiple blocks to avoid future contention on the + * relation extension lock. Our goal is to pre-extend the relation by an + * amount which ramps up as the degree of contention ramps up, but limiting + * the result to some sane overall value. + */ +static void +RelationAddExtraBlocks(Relation relation, BulkInsertState bistate) +{ + BlockNumber blockNum, + firstBlock = InvalidBlockNumber; + int extraBlocks; + int lockWaiters; + + /* Use the length of the lock wait queue to judge how much to extend. */ + lockWaiters = RelationExtensionLockWaiterCount(relation); + if (lockWaiters <= 0) + return; + + /* + * It might seem like multiplying the number of lock waiters by as much as + * 20 is too aggressive, but benchmarking revealed that smaller numbers + * were insufficient. 512 is just an arbitrary cap to prevent + * pathological results. + */ + extraBlocks = Min(512, lockWaiters * 20); + + do + { + Buffer buffer; + Page page; + Size freespace; + + /* + * Extend by one page. This should generally match the main-line + * extension code in RelationGetBufferForTuple, except that we hold + * the relation extension lock throughout, and we don't immediately + * initialize the page (see below). + */ + buffer = ReadBufferBI(relation, P_NEW, RBM_ZERO_AND_LOCK, bistate); + page = BufferGetPage(buffer); + + if (!PageIsNew(page)) + elog(ERROR, "page %u of relation \"%s\" should be empty but is not", + BufferGetBlockNumber(buffer), + RelationGetRelationName(relation)); + + /* + * Add the page to the FSM without initializing. If we were to + * initialize here, the page would potentially get flushed out to disk + * before we add any useful content. There's no guarantee that that'd + * happen before a potential crash, so we need to deal with + * uninitialized pages anyway, thus avoid the potential for + * unnecessary writes. + */ + + /* we'll need this info below */ + blockNum = BufferGetBlockNumber(buffer); + freespace = BufferGetPageSize(buffer) - SizeOfPageHeaderData; + + UnlockReleaseBuffer(buffer); + + /* Remember first block number thus added. */ + if (firstBlock == InvalidBlockNumber) + firstBlock = blockNum; + + /* + * Immediately update the bottom level of the FSM. This has a good + * chance of making this page visible to other concurrently inserting + * backends, and we want that to happen without delay. + */ + RecordPageWithFreeSpace(relation, blockNum, freespace); + } + while (--extraBlocks > 0); + + /* + * Updating the upper levels of the free space map is too expensive to do + * for every block, but it's worth doing once at the end to make sure that + * subsequent insertion activity sees all of those nifty free pages we + * just inserted. + */ + FreeSpaceMapVacuumRange(relation, firstBlock, blockNum + 1); +} + +/* + * RelationGetBufferForTuple + * + * Returns pinned and exclusive-locked buffer of a page in given relation + * with free space >= given len. + * + * If otherBuffer is not InvalidBuffer, then it references a previously + * pinned buffer of another page in the same relation; on return, this + * buffer will also be exclusive-locked. (This case is used by heap_update; + * the otherBuffer contains the tuple being updated.) + * + * The reason for passing otherBuffer is that if two backends are doing + * concurrent heap_update operations, a deadlock could occur if they try + * to lock the same two buffers in opposite orders. To ensure that this + * can't happen, we impose the rule that buffers of a relation must be + * locked in increasing page number order. This is most conveniently done + * by having RelationGetBufferForTuple lock them both, with suitable care + * for ordering. + * + * NOTE: it is unlikely, but not quite impossible, for otherBuffer to be the + * same buffer we select for insertion of the new tuple (this could only + * happen if space is freed in that page after heap_update finds there's not + * enough there). In that case, the page will be pinned and locked only once. + * + * We also handle the possibility that the all-visible flag will need to be + * cleared on one or both pages. If so, pin on the associated visibility map + * page must be acquired before acquiring buffer lock(s), to avoid possibly + * doing I/O while holding buffer locks. The pins are passed back to the + * caller using the input-output arguments vmbuffer and vmbuffer_other. + * Note that in some cases the caller might have already acquired such pins, + * which is indicated by these arguments not being InvalidBuffer on entry. + * + * We normally use FSM to help us find free space. However, + * if HEAP_INSERT_SKIP_FSM is specified, we just append a new empty page to + * the end of the relation if the tuple won't fit on the current target page. + * This can save some cycles when we know the relation is new and doesn't + * contain useful amounts of free space. + * + * HEAP_INSERT_SKIP_FSM is also useful for non-WAL-logged additions to a + * relation, if the caller holds exclusive lock and is careful to invalidate + * relation's smgr_targblock before the first insertion --- that ensures that + * all insertions will occur into newly added pages and not be intermixed + * with tuples from other transactions. That way, a crash can't risk losing + * any committed data of other transactions. (See heap_insert's comments + * for additional constraints needed for safe usage of this behavior.) + * + * The caller can also provide a BulkInsertState object to optimize many + * insertions into the same relation. This keeps a pin on the current + * insertion target page (to save pin/unpin cycles) and also passes a + * BULKWRITE buffer selection strategy object to the buffer manager. + * Passing NULL for bistate selects the default behavior. + * + * We always try to avoid filling existing pages further than the fillfactor. + * This is OK since this routine is not consulted when updating a tuple and + * keeping it on the same page, which is the scenario fillfactor is meant + * to reserve space for. + * + * ereport(ERROR) is allowed here, so this routine *must* be called + * before any (unlogged) changes are made in buffer pool. + */ +Buffer +RelationGetBufferForTuple(Relation relation, Size len, + Buffer otherBuffer, int options, + BulkInsertState bistate, + Buffer *vmbuffer, Buffer *vmbuffer_other) +{ + bool use_fsm = !(options & HEAP_INSERT_SKIP_FSM); + Buffer buffer = InvalidBuffer; + Page page; + Size pageFreeSpace = 0, + saveFreeSpace = 0; + BlockNumber targetBlock, + otherBlock; + bool needLock; + + len = MAXALIGN(len); /* be conservative */ + + /* Bulk insert is not supported for updates, only inserts. */ + Assert(otherBuffer == InvalidBuffer || !bistate); + + /* + * If we're gonna fail for oversize tuple, do it right away + */ + if (len > MaxHeapTupleSize) + ereport(ERROR, + (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED), + errmsg("row is too big: size %zu, maximum size %zu", + len, MaxHeapTupleSize))); + + /* Compute desired extra freespace due to fillfactor option */ + saveFreeSpace = RelationGetTargetPageFreeSpace(relation, + HEAP_DEFAULT_FILLFACTOR); + + if (otherBuffer != InvalidBuffer) + otherBlock = BufferGetBlockNumber(otherBuffer); + else + otherBlock = InvalidBlockNumber; /* just to keep compiler quiet */ + + /* + * We first try to put the tuple on the same page we last inserted a tuple + * on, as cached in the BulkInsertState or relcache entry. If that + * doesn't work, we ask the Free Space Map to locate a suitable page. + * Since the FSM's info might be out of date, we have to be prepared to + * loop around and retry multiple times. (To insure this isn't an infinite + * loop, we must update the FSM with the correct amount of free space on + * each page that proves not to be suitable.) If the FSM has no record of + * a page with enough free space, we give up and extend the relation. + * + * When use_fsm is false, we either put the tuple onto the existing target + * page or extend the relation. + */ + if (len + saveFreeSpace > MaxHeapTupleSize) + { + /* can't fit, don't bother asking FSM */ + targetBlock = InvalidBlockNumber; + use_fsm = false; + } + else if (bistate && bistate->current_buf != InvalidBuffer) + targetBlock = BufferGetBlockNumber(bistate->current_buf); + else + targetBlock = RelationGetTargetBlock(relation); + + if (targetBlock == InvalidBlockNumber && use_fsm) + { + /* + * We have no cached target page, so ask the FSM for an initial + * target. + */ + targetBlock = GetPageWithFreeSpace(relation, len + saveFreeSpace); + + /* + * If the FSM knows nothing of the rel, try the last page before we + * give up and extend. This avoids one-tuple-per-page syndrome during + * bootstrapping or in a recently-started system. + */ + if (targetBlock == InvalidBlockNumber) + { + BlockNumber nblocks = RelationGetNumberOfBlocks(relation); + + if (nblocks > 0) + targetBlock = nblocks - 1; + } + } + +loop: + while (targetBlock != InvalidBlockNumber) + { + /* + * Read and exclusive-lock the target block, as well as the other + * block if one was given, taking suitable care with lock ordering and + * the possibility they are the same block. + * + * If the page-level all-visible flag is set, caller will need to + * clear both that and the corresponding visibility map bit. However, + * by the time we return, we'll have x-locked the buffer, and we don't + * want to do any I/O while in that state. So we check the bit here + * before taking the lock, and pin the page if it appears necessary. + * Checking without the lock creates a risk of getting the wrong + * answer, so we'll have to recheck after acquiring the lock. + */ + if (otherBuffer == InvalidBuffer) + { + /* easy case */ + buffer = ReadBufferBI(relation, targetBlock, RBM_NORMAL, bistate); + if (PageIsAllVisible(BufferGetPage(buffer))) + visibilitymap_pin(relation, targetBlock, vmbuffer); + LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE); + } + else if (otherBlock == targetBlock) + { + /* also easy case */ + buffer = otherBuffer; + if (PageIsAllVisible(BufferGetPage(buffer))) + visibilitymap_pin(relation, targetBlock, vmbuffer); + LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE); + } + else if (otherBlock < targetBlock) + { + /* lock other buffer first */ + buffer = ReadBuffer(relation, targetBlock); + if (PageIsAllVisible(BufferGetPage(buffer))) + visibilitymap_pin(relation, targetBlock, vmbuffer); + LockBuffer(otherBuffer, BUFFER_LOCK_EXCLUSIVE); + LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE); + } + else + { + /* lock target buffer first */ + buffer = ReadBuffer(relation, targetBlock); + if (PageIsAllVisible(BufferGetPage(buffer))) + visibilitymap_pin(relation, targetBlock, vmbuffer); + LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE); + LockBuffer(otherBuffer, BUFFER_LOCK_EXCLUSIVE); + } + + /* + * We now have the target page (and the other buffer, if any) pinned + * and locked. However, since our initial PageIsAllVisible checks + * were performed before acquiring the lock, the results might now be + * out of date, either for the selected victim buffer, or for the + * other buffer passed by the caller. In that case, we'll need to + * give up our locks, go get the pin(s) we failed to get earlier, and + * re-lock. That's pretty painful, but hopefully shouldn't happen + * often. + * + * Note that there's a small possibility that we didn't pin the page + * above but still have the correct page pinned anyway, either because + * we've already made a previous pass through this loop, or because + * caller passed us the right page anyway. + * + * Note also that it's possible that by the time we get the pin and + * retake the buffer locks, the visibility map bit will have been + * cleared by some other backend anyway. In that case, we'll have + * done a bit of extra work for no gain, but there's no real harm + * done. + */ + if (otherBuffer == InvalidBuffer || targetBlock <= otherBlock) + GetVisibilityMapPins(relation, buffer, otherBuffer, + targetBlock, otherBlock, vmbuffer, + vmbuffer_other); + else + GetVisibilityMapPins(relation, otherBuffer, buffer, + otherBlock, targetBlock, vmbuffer_other, + vmbuffer); + + /* + * Now we can check to see if there's enough free space here. If so, + * we're done. + */ + page = BufferGetPage(buffer); + + /* + * If necessary initialize page, it'll be used soon. We could avoid + * dirtying the buffer here, and rely on the caller to do so whenever + * it puts a tuple onto the page, but there seems not much benefit in + * doing so. + */ + if (PageIsNew(page)) + { + PageInit(page, BufferGetPageSize(buffer), 0); + MarkBufferDirty(buffer); + } + + pageFreeSpace = PageGetHeapFreeSpace(page); + if (len + saveFreeSpace <= pageFreeSpace) + { + /* use this page as future insert target, too */ + RelationSetTargetBlock(relation, targetBlock); + return buffer; + } + + /* + * Not enough space, so we must give up our page locks and pin (if + * any) and prepare to look elsewhere. We don't care which order we + * unlock the two buffers in, so this can be slightly simpler than the + * code above. + */ + LockBuffer(buffer, BUFFER_LOCK_UNLOCK); + if (otherBuffer == InvalidBuffer) + ReleaseBuffer(buffer); + else if (otherBlock != targetBlock) + { + LockBuffer(otherBuffer, BUFFER_LOCK_UNLOCK); + ReleaseBuffer(buffer); + } + + /* Without FSM, always fall out of the loop and extend */ + if (!use_fsm) + break; + + /* + * Update FSM as to condition of this page, and ask for another page + * to try. + */ + targetBlock = RecordAndGetPageWithFreeSpace(relation, + targetBlock, + pageFreeSpace, + len + saveFreeSpace); + } + + /* + * Have to extend the relation. + * + * We have to use a lock to ensure no one else is extending the rel at the + * same time, else we will both try to initialize the same new page. We + * can skip locking for new or temp relations, however, since no one else + * could be accessing them. + */ + needLock = !RELATION_IS_LOCAL(relation); + + /* + * If we need the lock but are not able to acquire it immediately, we'll + * consider extending the relation by multiple blocks at a time to manage + * contention on the relation extension lock. However, this only makes + * sense if we're using the FSM; otherwise, there's no point. + */ + if (needLock) + { + if (!use_fsm) + LockRelationForExtension(relation, ExclusiveLock); + else if (!ConditionalLockRelationForExtension(relation, ExclusiveLock)) + { + /* Couldn't get the lock immediately; wait for it. */ + LockRelationForExtension(relation, ExclusiveLock); + + /* + * Check if some other backend has extended a block for us while + * we were waiting on the lock. + */ + targetBlock = GetPageWithFreeSpace(relation, len + saveFreeSpace); + + /* + * If some other waiter has already extended the relation, we + * don't need to do so; just use the existing freespace. + */ + if (targetBlock != InvalidBlockNumber) + { + UnlockRelationForExtension(relation, ExclusiveLock); + goto loop; + } + + /* Time to bulk-extend. */ + RelationAddExtraBlocks(relation, bistate); + } + } + + /* + * In addition to whatever extension we performed above, we always add at + * least one block to satisfy our own request. + * + * XXX This does an lseek - rather expensive - but at the moment it is the + * only way to accurately determine how many blocks are in a relation. Is + * it worth keeping an accurate file length in shared memory someplace, + * rather than relying on the kernel to do it for us? + */ + buffer = ReadBufferBI(relation, P_NEW, RBM_ZERO_AND_LOCK, bistate); + + /* + * We need to initialize the empty new page. Double-check that it really + * is empty (this should never happen, but if it does we don't want to + * risk wiping out valid data). + */ + page = BufferGetPage(buffer); + + if (!PageIsNew(page)) + elog(ERROR, "page %u of relation \"%s\" should be empty but is not", + BufferGetBlockNumber(buffer), + RelationGetRelationName(relation)); + + PageInit(page, BufferGetPageSize(buffer), 0); + MarkBufferDirty(buffer); + + /* + * Release the file-extension lock; it's now OK for someone else to extend + * the relation some more. + */ + if (needLock) + UnlockRelationForExtension(relation, ExclusiveLock); + + /* + * Lock the other buffer. It's guaranteed to be of a lower page number + * than the new page. To conform with the deadlock prevent rules, we ought + * to lock otherBuffer first, but that would give other backends a chance + * to put tuples on our page. To reduce the likelihood of that, attempt to + * lock the other buffer conditionally, that's very likely to work. + * Otherwise we need to lock buffers in the correct order, and retry if + * the space has been used in the mean time. + * + * Alternatively, we could acquire the lock on otherBuffer before + * extending the relation, but that'd require holding the lock while + * performing IO, which seems worse than an unlikely retry. + */ + if (otherBuffer != InvalidBuffer) + { + Assert(otherBuffer != buffer); + targetBlock = BufferGetBlockNumber(buffer); + Assert(targetBlock > otherBlock); + + if (unlikely(!ConditionalLockBuffer(otherBuffer))) + { + LockBuffer(buffer, BUFFER_LOCK_UNLOCK); + LockBuffer(otherBuffer, BUFFER_LOCK_EXCLUSIVE); + LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE); + + /* + * Because the buffers were unlocked for a while, it's possible, + * although unlikely, that an all-visible flag became set or that + * somebody used up the available space in the new page. We can + * use GetVisibilityMapPins to deal with the first case. In the + * second case, just retry from start. + */ + GetVisibilityMapPins(relation, otherBuffer, buffer, + otherBlock, targetBlock, vmbuffer_other, + vmbuffer); + + if (len > PageGetHeapFreeSpace(page)) + { + LockBuffer(otherBuffer, BUFFER_LOCK_UNLOCK); + UnlockReleaseBuffer(buffer); + + goto loop; + } + } + } + + if (len > PageGetHeapFreeSpace(page)) + { + /* We should not get here given the test at the top */ + elog(PANIC, "tuple is too big: size %zu", len); + } + + /* + * Remember the new page as our target for future insertions. + * + * XXX should we enter the new page into the free space map immediately, + * or just keep it for this backend's exclusive use in the short run + * (until VACUUM sees it)? Seems to depend on whether you expect the + * current backend to make more insertions or not, which is probably a + * good bet most of the time. So for now, don't add it to FSM yet. + */ + RelationSetTargetBlock(relation, BufferGetBlockNumber(buffer)); + + return buffer; +} |