/*------------------------------------------------------------------------- * * hashpage.c * Hash table page management code for the Postgres hash access method * * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group * Portions Copyright (c) 1994, Regents of the University of California * * * IDENTIFICATION * src/backend/access/hash/hashpage.c * * NOTES * Postgres hash pages look like ordinary relation pages. The opaque * data at high addresses includes information about the page including * whether a page is an overflow page or a true bucket, the bucket * number, and the block numbers of the preceding and following pages * in the same bucket. * * The first page in a hash relation, page zero, is special -- it stores * information describing the hash table; it is referred to as the * "meta page." Pages one and higher store the actual data. * * There are also bitmap pages, which are not manipulated here; * see hashovfl.c. * *------------------------------------------------------------------------- */ #include "postgres.h" #include "access/hash.h" #include "access/hash_xlog.h" #include "miscadmin.h" #include "storage/lmgr.h" #include "storage/predicate.h" #include "storage/smgr.h" static bool _hash_alloc_buckets(Relation rel, BlockNumber firstblock, uint32 nblocks); static void _hash_splitbucket(Relation rel, Buffer metabuf, Bucket obucket, Bucket nbucket, Buffer obuf, Buffer nbuf, HTAB *htab, uint32 maxbucket, uint32 highmask, uint32 lowmask); static void log_split_page(Relation rel, Buffer buf); /* * _hash_getbuf() -- Get a buffer by block number for read or write. * * 'access' must be HASH_READ, HASH_WRITE, or HASH_NOLOCK. * 'flags' is a bitwise OR of the allowed page types. * * This must be used only to fetch pages that are expected to be valid * already. _hash_checkpage() is applied using the given flags. * * When this routine returns, the appropriate lock is set on the * requested buffer and its reference count has been incremented * (ie, the buffer is "locked and pinned"). * * P_NEW is disallowed because this routine can only be used * to access pages that are known to be before the filesystem EOF. * Extending the index should be done with _hash_getnewbuf. */ Buffer _hash_getbuf(Relation rel, BlockNumber blkno, int access, int flags) { Buffer buf; if (blkno == P_NEW) elog(ERROR, "hash AM does not use P_NEW"); buf = ReadBuffer(rel, blkno); if (access != HASH_NOLOCK) LockBuffer(buf, access); /* ref count and lock type are correct */ _hash_checkpage(rel, buf, flags); return buf; } /* * _hash_getbuf_with_condlock_cleanup() -- Try to get a buffer for cleanup. * * We read the page and try to acquire a cleanup lock. If we get it, * we return the buffer; otherwise, we return InvalidBuffer. */ Buffer _hash_getbuf_with_condlock_cleanup(Relation rel, BlockNumber blkno, int flags) { Buffer buf; if (blkno == P_NEW) elog(ERROR, "hash AM does not use P_NEW"); buf = ReadBuffer(rel, blkno); if (!ConditionalLockBufferForCleanup(buf)) { ReleaseBuffer(buf); return InvalidBuffer; } /* ref count and lock type are correct */ _hash_checkpage(rel, buf, flags); return buf; } /* * _hash_getinitbuf() -- Get and initialize a buffer by block number. * * This must be used only to fetch pages that are known to be before * the index's filesystem EOF, but are to be filled from scratch. * _hash_pageinit() is applied automatically. Otherwise it has * effects similar to _hash_getbuf() with access = HASH_WRITE. * * When this routine returns, a write lock is set on the * requested buffer and its reference count has been incremented * (ie, the buffer is "locked and pinned"). * * P_NEW is disallowed because this routine can only be used * to access pages that are known to be before the filesystem EOF. * Extending the index should be done with _hash_getnewbuf. */ Buffer _hash_getinitbuf(Relation rel, BlockNumber blkno) { Buffer buf; if (blkno == P_NEW) elog(ERROR, "hash AM does not use P_NEW"); buf = ReadBufferExtended(rel, MAIN_FORKNUM, blkno, RBM_ZERO_AND_LOCK, NULL); /* ref count and lock type are correct */ /* initialize the page */ _hash_pageinit(BufferGetPage(buf), BufferGetPageSize(buf)); return buf; } /* * _hash_initbuf() -- Get and initialize a buffer by bucket number. */ void _hash_initbuf(Buffer buf, uint32 max_bucket, uint32 num_bucket, uint32 flag, bool initpage) { HashPageOpaque pageopaque; Page page; page = BufferGetPage(buf); /* initialize the page */ if (initpage) _hash_pageinit(page, BufferGetPageSize(buf)); pageopaque = (HashPageOpaque) PageGetSpecialPointer(page); /* * Set hasho_prevblkno with current hashm_maxbucket. This value will be * used to validate cached HashMetaPageData. See * _hash_getbucketbuf_from_hashkey(). */ pageopaque->hasho_prevblkno = max_bucket; pageopaque->hasho_nextblkno = InvalidBlockNumber; pageopaque->hasho_bucket = num_bucket; pageopaque->hasho_flag = flag; pageopaque->hasho_page_id = HASHO_PAGE_ID; } /* * _hash_getnewbuf() -- Get a new page at the end of the index. * * This has the same API as _hash_getinitbuf, except that we are adding * a page to the index, and hence expect the page to be past the * logical EOF. (However, we have to support the case where it isn't, * since a prior try might have crashed after extending the filesystem * EOF but before updating the metapage to reflect the added page.) * * It is caller's responsibility to ensure that only one process can * extend the index at a time. In practice, this function is called * only while holding write lock on the metapage, because adding a page * is always associated with an update of metapage data. */ Buffer _hash_getnewbuf(Relation rel, BlockNumber blkno, ForkNumber forkNum) { BlockNumber nblocks = RelationGetNumberOfBlocksInFork(rel, forkNum); Buffer buf; if (blkno == P_NEW) elog(ERROR, "hash AM does not use P_NEW"); if (blkno > nblocks) elog(ERROR, "access to noncontiguous page in hash index \"%s\"", RelationGetRelationName(rel)); /* smgr insists we use P_NEW to extend the relation */ if (blkno == nblocks) { buf = ReadBufferExtended(rel, forkNum, P_NEW, RBM_NORMAL, NULL); if (BufferGetBlockNumber(buf) != blkno) elog(ERROR, "unexpected hash relation size: %u, should be %u", BufferGetBlockNumber(buf), blkno); LockBuffer(buf, HASH_WRITE); } else { buf = ReadBufferExtended(rel, forkNum, blkno, RBM_ZERO_AND_LOCK, NULL); } /* ref count and lock type are correct */ /* initialize the page */ _hash_pageinit(BufferGetPage(buf), BufferGetPageSize(buf)); return buf; } /* * _hash_getbuf_with_strategy() -- Get a buffer with nondefault strategy. * * This is identical to _hash_getbuf() but also allows a buffer access * strategy to be specified. We use this for VACUUM operations. */ Buffer _hash_getbuf_with_strategy(Relation rel, BlockNumber blkno, int access, int flags, BufferAccessStrategy bstrategy) { Buffer buf; if (blkno == P_NEW) elog(ERROR, "hash AM does not use P_NEW"); buf = ReadBufferExtended(rel, MAIN_FORKNUM, blkno, RBM_NORMAL, bstrategy); if (access != HASH_NOLOCK) LockBuffer(buf, access); /* ref count and lock type are correct */ _hash_checkpage(rel, buf, flags); return buf; } /* * _hash_relbuf() -- release a locked buffer. * * Lock and pin (refcount) are both dropped. */ void _hash_relbuf(Relation rel, Buffer buf) { UnlockReleaseBuffer(buf); } /* * _hash_dropbuf() -- release an unlocked buffer. * * This is used to unpin a buffer on which we hold no lock. */ void _hash_dropbuf(Relation rel, Buffer buf) { ReleaseBuffer(buf); } /* * _hash_dropscanbuf() -- release buffers used in scan. * * This routine unpins the buffers used during scan on which we * hold no lock. */ void _hash_dropscanbuf(Relation rel, HashScanOpaque so) { /* release pin we hold on primary bucket page */ if (BufferIsValid(so->hashso_bucket_buf) && so->hashso_bucket_buf != so->currPos.buf) _hash_dropbuf(rel, so->hashso_bucket_buf); so->hashso_bucket_buf = InvalidBuffer; /* release pin we hold on primary bucket page of bucket being split */ if (BufferIsValid(so->hashso_split_bucket_buf) && so->hashso_split_bucket_buf != so->currPos.buf) _hash_dropbuf(rel, so->hashso_split_bucket_buf); so->hashso_split_bucket_buf = InvalidBuffer; /* release any pin we still hold */ if (BufferIsValid(so->currPos.buf)) _hash_dropbuf(rel, so->currPos.buf); so->currPos.buf = InvalidBuffer; /* reset split scan */ so->hashso_buc_populated = false; so->hashso_buc_split = false; } /* * _hash_init() -- Initialize the metadata page of a hash index, * the initial buckets, and the initial bitmap page. * * The initial number of buckets is dependent on num_tuples, an estimate * of the number of tuples to be loaded into the index initially. The * chosen number of buckets is returned. * * We are fairly cavalier about locking here, since we know that no one else * could be accessing this index. In particular the rule about not holding * multiple buffer locks is ignored. */ uint32 _hash_init(Relation rel, double num_tuples, ForkNumber forkNum) { Buffer metabuf; Buffer buf; Buffer bitmapbuf; Page pg; HashMetaPage metap; RegProcedure procid; int32 data_width; int32 item_width; int32 ffactor; uint32 num_buckets; uint32 i; bool use_wal; /* safety check */ if (RelationGetNumberOfBlocksInFork(rel, forkNum) != 0) elog(ERROR, "cannot initialize non-empty hash index \"%s\"", RelationGetRelationName(rel)); /* * WAL log creation of pages if the relation is persistent, or this is the * init fork. Init forks for unlogged relations always need to be WAL * logged. */ use_wal = RelationNeedsWAL(rel) || forkNum == INIT_FORKNUM; /* * Determine the target fill factor (in tuples per bucket) for this index. * The idea is to make the fill factor correspond to pages about as full * as the user-settable fillfactor parameter says. We can compute it * exactly since the index datatype (i.e. uint32 hash key) is fixed-width. */ data_width = sizeof(uint32); item_width = MAXALIGN(sizeof(IndexTupleData)) + MAXALIGN(data_width) + sizeof(ItemIdData); /* include the line pointer */ ffactor = RelationGetTargetPageUsage(rel, HASH_DEFAULT_FILLFACTOR) / item_width; /* keep to a sane range */ if (ffactor < 10) ffactor = 10; procid = index_getprocid(rel, 1, HASHSTANDARD_PROC); /* * We initialize the metapage, the first N bucket pages, and the first * bitmap page in sequence, using _hash_getnewbuf to cause smgrextend() * calls to occur. This ensures that the smgr level has the right idea of * the physical index length. * * Critical section not required, because on error the creation of the * whole relation will be rolled back. */ metabuf = _hash_getnewbuf(rel, HASH_METAPAGE, forkNum); _hash_init_metabuffer(metabuf, num_tuples, procid, ffactor, false); MarkBufferDirty(metabuf); pg = BufferGetPage(metabuf); metap = HashPageGetMeta(pg); /* XLOG stuff */ if (use_wal) { xl_hash_init_meta_page xlrec; XLogRecPtr recptr; xlrec.num_tuples = num_tuples; xlrec.procid = metap->hashm_procid; xlrec.ffactor = metap->hashm_ffactor; XLogBeginInsert(); XLogRegisterData((char *) &xlrec, SizeOfHashInitMetaPage); XLogRegisterBuffer(0, metabuf, REGBUF_WILL_INIT | REGBUF_STANDARD); recptr = XLogInsert(RM_HASH_ID, XLOG_HASH_INIT_META_PAGE); PageSetLSN(BufferGetPage(metabuf), recptr); } num_buckets = metap->hashm_maxbucket + 1; /* * Release buffer lock on the metapage while we initialize buckets. * Otherwise, we'll be in interrupt holdoff and the CHECK_FOR_INTERRUPTS * won't accomplish anything. It's a bad idea to hold buffer locks for * long intervals in any case, since that can block the bgwriter. */ LockBuffer(metabuf, BUFFER_LOCK_UNLOCK); /* * Initialize and WAL Log the first N buckets */ for (i = 0; i < num_buckets; i++) { BlockNumber blkno; /* Allow interrupts, in case N is huge */ CHECK_FOR_INTERRUPTS(); blkno = BUCKET_TO_BLKNO(metap, i); buf = _hash_getnewbuf(rel, blkno, forkNum); _hash_initbuf(buf, metap->hashm_maxbucket, i, LH_BUCKET_PAGE, false); MarkBufferDirty(buf); if (use_wal) log_newpage(&rel->rd_node, forkNum, blkno, BufferGetPage(buf), true); _hash_relbuf(rel, buf); } /* Now reacquire buffer lock on metapage */ LockBuffer(metabuf, BUFFER_LOCK_EXCLUSIVE); /* * Initialize bitmap page */ bitmapbuf = _hash_getnewbuf(rel, num_buckets + 1, forkNum); _hash_initbitmapbuffer(bitmapbuf, metap->hashm_bmsize, false); MarkBufferDirty(bitmapbuf); /* add the new bitmap page to the metapage's list of bitmaps */ /* metapage already has a write lock */ if (metap->hashm_nmaps >= HASH_MAX_BITMAPS) ereport(ERROR, (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED), errmsg("out of overflow pages in hash index \"%s\"", RelationGetRelationName(rel)))); metap->hashm_mapp[metap->hashm_nmaps] = num_buckets + 1; metap->hashm_nmaps++; MarkBufferDirty(metabuf); /* XLOG stuff */ if (use_wal) { xl_hash_init_bitmap_page xlrec; XLogRecPtr recptr; xlrec.bmsize = metap->hashm_bmsize; XLogBeginInsert(); XLogRegisterData((char *) &xlrec, SizeOfHashInitBitmapPage); XLogRegisterBuffer(0, bitmapbuf, REGBUF_WILL_INIT); /* * This is safe only because nobody else can be modifying the index at * this stage; it's only visible to the transaction that is creating * it. */ XLogRegisterBuffer(1, metabuf, REGBUF_STANDARD); recptr = XLogInsert(RM_HASH_ID, XLOG_HASH_INIT_BITMAP_PAGE); PageSetLSN(BufferGetPage(bitmapbuf), recptr); PageSetLSN(BufferGetPage(metabuf), recptr); } /* all done */ _hash_relbuf(rel, bitmapbuf); _hash_relbuf(rel, metabuf); return num_buckets; } /* * _hash_init_metabuffer() -- Initialize the metadata page of a hash index. */ void _hash_init_metabuffer(Buffer buf, double num_tuples, RegProcedure procid, uint16 ffactor, bool initpage) { HashMetaPage metap; HashPageOpaque pageopaque; Page page; double dnumbuckets; uint32 num_buckets; uint32 spare_index; uint32 i; /* * Choose the number of initial bucket pages to match the fill factor * given the estimated number of tuples. We round up the result to the * total number of buckets which has to be allocated before using its * hashm_spares element. However always force at least 2 bucket pages. The * upper limit is determined by considerations explained in * _hash_expandtable(). */ dnumbuckets = num_tuples / ffactor; if (dnumbuckets <= 2.0) num_buckets = 2; else if (dnumbuckets >= (double) 0x40000000) num_buckets = 0x40000000; else num_buckets = _hash_get_totalbuckets(_hash_spareindex(dnumbuckets)); spare_index = _hash_spareindex(num_buckets); Assert(spare_index < HASH_MAX_SPLITPOINTS); page = BufferGetPage(buf); if (initpage) _hash_pageinit(page, BufferGetPageSize(buf)); pageopaque = (HashPageOpaque) PageGetSpecialPointer(page); pageopaque->hasho_prevblkno = InvalidBlockNumber; pageopaque->hasho_nextblkno = InvalidBlockNumber; pageopaque->hasho_bucket = -1; pageopaque->hasho_flag = LH_META_PAGE; pageopaque->hasho_page_id = HASHO_PAGE_ID; metap = HashPageGetMeta(page); metap->hashm_magic = HASH_MAGIC; metap->hashm_version = HASH_VERSION; metap->hashm_ntuples = 0; metap->hashm_nmaps = 0; metap->hashm_ffactor = ffactor; metap->hashm_bsize = HashGetMaxBitmapSize(page); /* find largest bitmap array size that will fit in page size */ for (i = _hash_log2(metap->hashm_bsize); i > 0; --i) { if ((1 << i) <= metap->hashm_bsize) break; } Assert(i > 0); metap->hashm_bmsize = 1 << i; metap->hashm_bmshift = i + BYTE_TO_BIT; Assert((1 << BMPG_SHIFT(metap)) == (BMPG_MASK(metap) + 1)); /* * Label the index with its primary hash support function's OID. This is * pretty useless for normal operation (in fact, hashm_procid is not used * anywhere), but it might be handy for forensic purposes so we keep it. */ metap->hashm_procid = procid; /* * We initialize the index with N buckets, 0 .. N-1, occupying physical * blocks 1 to N. The first freespace bitmap page is in block N+1. */ metap->hashm_maxbucket = num_buckets - 1; /* * Set highmask as next immediate ((2 ^ x) - 1), which should be * sufficient to cover num_buckets. */ metap->hashm_highmask = (1 << (_hash_log2(num_buckets + 1))) - 1; metap->hashm_lowmask = (metap->hashm_highmask >> 1); MemSet(metap->hashm_spares, 0, sizeof(metap->hashm_spares)); MemSet(metap->hashm_mapp, 0, sizeof(metap->hashm_mapp)); /* Set up mapping for one spare page after the initial splitpoints */ metap->hashm_spares[spare_index] = 1; metap->hashm_ovflpoint = spare_index; metap->hashm_firstfree = 0; /* * Set pd_lower just past the end of the metadata. This is essential, * because without doing so, metadata will be lost if xlog.c compresses * the page. */ ((PageHeader) page)->pd_lower = ((char *) metap + sizeof(HashMetaPageData)) - (char *) page; } /* * _hash_pageinit() -- Initialize a new hash index page. */ void _hash_pageinit(Page page, Size size) { PageInit(page, size, sizeof(HashPageOpaqueData)); } /* * Attempt to expand the hash table by creating one new bucket. * * This will silently do nothing if we don't get cleanup lock on old or * new bucket. * * Complete the pending splits and remove the tuples from old bucket, * if there are any left over from the previous split. * * The caller must hold a pin, but no lock, on the metapage buffer. * The buffer is returned in the same state. */ void _hash_expandtable(Relation rel, Buffer metabuf) { HashMetaPage metap; Bucket old_bucket; Bucket new_bucket; uint32 spare_ndx; BlockNumber start_oblkno; BlockNumber start_nblkno; Buffer buf_nblkno; Buffer buf_oblkno; Page opage; Page npage; HashPageOpaque oopaque; HashPageOpaque nopaque; uint32 maxbucket; uint32 highmask; uint32 lowmask; bool metap_update_masks = false; bool metap_update_splitpoint = false; restart_expand: /* * Write-lock the meta page. It used to be necessary to acquire a * heavyweight lock to begin a split, but that is no longer required. */ LockBuffer(metabuf, BUFFER_LOCK_EXCLUSIVE); _hash_checkpage(rel, metabuf, LH_META_PAGE); metap = HashPageGetMeta(BufferGetPage(metabuf)); /* * Check to see if split is still needed; someone else might have already * done one while we waited for the lock. * * Make sure this stays in sync with _hash_doinsert() */ if (metap->hashm_ntuples <= (double) metap->hashm_ffactor * (metap->hashm_maxbucket + 1)) goto fail; /* * Can't split anymore if maxbucket has reached its maximum possible * value. * * Ideally we'd allow bucket numbers up to UINT_MAX-1 (no higher because * the calculation maxbucket+1 mustn't overflow). Currently we restrict * to half that because of overflow looping in _hash_log2() and * insufficient space in hashm_spares[]. It's moot anyway because an * index with 2^32 buckets would certainly overflow BlockNumber and hence * _hash_alloc_buckets() would fail, but if we supported buckets smaller * than a disk block then this would be an independent constraint. * * If you change this, see also the maximum initial number of buckets in * _hash_init(). */ if (metap->hashm_maxbucket >= (uint32) 0x7FFFFFFE) goto fail; /* * Determine which bucket is to be split, and attempt to take cleanup lock * on the old bucket. If we can't get the lock, give up. * * The cleanup lock protects us not only against other backends, but * against our own backend as well. * * The cleanup lock is mainly to protect the split from concurrent * inserts. See src/backend/access/hash/README, Lock Definitions for * further details. Due to this locking restriction, if there is any * pending scan, the split will give up which is not good, but harmless. */ new_bucket = metap->hashm_maxbucket + 1; old_bucket = (new_bucket & metap->hashm_lowmask); start_oblkno = BUCKET_TO_BLKNO(metap, old_bucket); buf_oblkno = _hash_getbuf_with_condlock_cleanup(rel, start_oblkno, LH_BUCKET_PAGE); if (!buf_oblkno) goto fail; opage = BufferGetPage(buf_oblkno); oopaque = (HashPageOpaque) PageGetSpecialPointer(opage); /* * We want to finish the split from a bucket as there is no apparent * benefit by not doing so and it will make the code complicated to finish * the split that involves multiple buckets considering the case where new * split also fails. We don't need to consider the new bucket for * completing the split here as it is not possible that a re-split of new * bucket starts when there is still a pending split from old bucket. */ if (H_BUCKET_BEING_SPLIT(oopaque)) { /* * Copy bucket mapping info now; refer the comment in code below where * we copy this information before calling _hash_splitbucket to see * why this is okay. */ maxbucket = metap->hashm_maxbucket; highmask = metap->hashm_highmask; lowmask = metap->hashm_lowmask; /* * Release the lock on metapage and old_bucket, before completing the * split. */ LockBuffer(metabuf, BUFFER_LOCK_UNLOCK); LockBuffer(buf_oblkno, BUFFER_LOCK_UNLOCK); _hash_finish_split(rel, metabuf, buf_oblkno, old_bucket, maxbucket, highmask, lowmask); /* release the pin on old buffer and retry for expand. */ _hash_dropbuf(rel, buf_oblkno); goto restart_expand; } /* * Clean the tuples remained from the previous split. This operation * requires cleanup lock and we already have one on the old bucket, so * let's do it. We also don't want to allow further splits from the bucket * till the garbage of previous split is cleaned. This has two * advantages; first, it helps in avoiding the bloat due to garbage and * second is, during cleanup of bucket, we are always sure that the * garbage tuples belong to most recently split bucket. On the contrary, * if we allow cleanup of bucket after meta page is updated to indicate * the new split and before the actual split, the cleanup operation won't * be able to decide whether the tuple has been moved to the newly created * bucket and ended up deleting such tuples. */ if (H_NEEDS_SPLIT_CLEANUP(oopaque)) { /* * Copy bucket mapping info now; refer to the comment in code below * where we copy this information before calling _hash_splitbucket to * see why this is okay. */ maxbucket = metap->hashm_maxbucket; highmask = metap->hashm_highmask; lowmask = metap->hashm_lowmask; /* Release the metapage lock. */ LockBuffer(metabuf, BUFFER_LOCK_UNLOCK); hashbucketcleanup(rel, old_bucket, buf_oblkno, start_oblkno, NULL, maxbucket, highmask, lowmask, NULL, NULL, true, NULL, NULL); _hash_dropbuf(rel, buf_oblkno); goto restart_expand; } /* * There shouldn't be any active scan on new bucket. * * Note: it is safe to compute the new bucket's blkno here, even though we * may still need to update the BUCKET_TO_BLKNO mapping. This is because * the current value of hashm_spares[hashm_ovflpoint] correctly shows * where we are going to put a new splitpoint's worth of buckets. */ start_nblkno = BUCKET_TO_BLKNO(metap, new_bucket); /* * If the split point is increasing we need to allocate a new batch of * bucket pages. */ spare_ndx = _hash_spareindex(new_bucket + 1); if (spare_ndx > metap->hashm_ovflpoint) { uint32 buckets_to_add; Assert(spare_ndx == metap->hashm_ovflpoint + 1); /* * We treat allocation of buckets as a separate WAL-logged action. * Even if we fail after this operation, won't leak bucket pages; * rather, the next split will consume this space. In any case, even * without failure we don't use all the space in one split operation. */ buckets_to_add = _hash_get_totalbuckets(spare_ndx) - new_bucket; if (!_hash_alloc_buckets(rel, start_nblkno, buckets_to_add)) { /* can't split due to BlockNumber overflow */ _hash_relbuf(rel, buf_oblkno); goto fail; } } /* * Physically allocate the new bucket's primary page. We want to do this * before changing the metapage's mapping info, in case we can't get the * disk space. Ideally, we don't need to check for cleanup lock on new * bucket as no other backend could find this bucket unless meta page is * updated. However, it is good to be consistent with old bucket locking. */ buf_nblkno = _hash_getnewbuf(rel, start_nblkno, MAIN_FORKNUM); if (!IsBufferCleanupOK(buf_nblkno)) { _hash_relbuf(rel, buf_oblkno); _hash_relbuf(rel, buf_nblkno); goto fail; } /* * Since we are scribbling on the pages in the shared buffers, establish a * critical section. Any failure in this next code leaves us with a big * problem: the metapage is effectively corrupt but could get written back * to disk. */ START_CRIT_SECTION(); /* * Okay to proceed with split. Update the metapage bucket mapping info. */ metap->hashm_maxbucket = new_bucket; if (new_bucket > metap->hashm_highmask) { /* Starting a new doubling */ metap->hashm_lowmask = metap->hashm_highmask; metap->hashm_highmask = new_bucket | metap->hashm_lowmask; metap_update_masks = true; } /* * If the split point is increasing we need to adjust the hashm_spares[] * array and hashm_ovflpoint so that future overflow pages will be created * beyond this new batch of bucket pages. */ if (spare_ndx > metap->hashm_ovflpoint) { metap->hashm_spares[spare_ndx] = metap->hashm_spares[metap->hashm_ovflpoint]; metap->hashm_ovflpoint = spare_ndx; metap_update_splitpoint = true; } MarkBufferDirty(metabuf); /* * Copy bucket mapping info now; this saves re-accessing the meta page * inside _hash_splitbucket's inner loop. Note that once we drop the * split lock, other splits could begin, so these values might be out of * date before _hash_splitbucket finishes. That's okay, since all it * needs is to tell which of these two buckets to map hashkeys into. */ maxbucket = metap->hashm_maxbucket; highmask = metap->hashm_highmask; lowmask = metap->hashm_lowmask; opage = BufferGetPage(buf_oblkno); oopaque = (HashPageOpaque) PageGetSpecialPointer(opage); /* * Mark the old bucket to indicate that split is in progress. (At * operation end, we will clear the split-in-progress flag.) Also, for a * primary bucket page, hasho_prevblkno stores the number of buckets that * existed as of the last split, so we must update that value here. */ oopaque->hasho_flag |= LH_BUCKET_BEING_SPLIT; oopaque->hasho_prevblkno = maxbucket; MarkBufferDirty(buf_oblkno); npage = BufferGetPage(buf_nblkno); /* * initialize the new bucket's primary page and mark it to indicate that * split is in progress. */ nopaque = (HashPageOpaque) PageGetSpecialPointer(npage); nopaque->hasho_prevblkno = maxbucket; nopaque->hasho_nextblkno = InvalidBlockNumber; nopaque->hasho_bucket = new_bucket; nopaque->hasho_flag = LH_BUCKET_PAGE | LH_BUCKET_BEING_POPULATED; nopaque->hasho_page_id = HASHO_PAGE_ID; MarkBufferDirty(buf_nblkno); /* XLOG stuff */ if (RelationNeedsWAL(rel)) { xl_hash_split_allocate_page xlrec; XLogRecPtr recptr; xlrec.new_bucket = maxbucket; xlrec.old_bucket_flag = oopaque->hasho_flag; xlrec.new_bucket_flag = nopaque->hasho_flag; xlrec.flags = 0; XLogBeginInsert(); XLogRegisterBuffer(0, buf_oblkno, REGBUF_STANDARD); XLogRegisterBuffer(1, buf_nblkno, REGBUF_WILL_INIT); XLogRegisterBuffer(2, metabuf, REGBUF_STANDARD); if (metap_update_masks) { xlrec.flags |= XLH_SPLIT_META_UPDATE_MASKS; XLogRegisterBufData(2, (char *) &metap->hashm_lowmask, sizeof(uint32)); XLogRegisterBufData(2, (char *) &metap->hashm_highmask, sizeof(uint32)); } if (metap_update_splitpoint) { xlrec.flags |= XLH_SPLIT_META_UPDATE_SPLITPOINT; XLogRegisterBufData(2, (char *) &metap->hashm_ovflpoint, sizeof(uint32)); XLogRegisterBufData(2, (char *) &metap->hashm_spares[metap->hashm_ovflpoint], sizeof(uint32)); } XLogRegisterData((char *) &xlrec, SizeOfHashSplitAllocPage); recptr = XLogInsert(RM_HASH_ID, XLOG_HASH_SPLIT_ALLOCATE_PAGE); PageSetLSN(BufferGetPage(buf_oblkno), recptr); PageSetLSN(BufferGetPage(buf_nblkno), recptr); PageSetLSN(BufferGetPage(metabuf), recptr); } END_CRIT_SECTION(); /* drop lock, but keep pin */ LockBuffer(metabuf, BUFFER_LOCK_UNLOCK); /* Relocate records to the new bucket */ _hash_splitbucket(rel, metabuf, old_bucket, new_bucket, buf_oblkno, buf_nblkno, NULL, maxbucket, highmask, lowmask); /* all done, now release the pins on primary buckets. */ _hash_dropbuf(rel, buf_oblkno); _hash_dropbuf(rel, buf_nblkno); return; /* Here if decide not to split or fail to acquire old bucket lock */ fail: /* We didn't write the metapage, so just drop lock */ LockBuffer(metabuf, BUFFER_LOCK_UNLOCK); } /* * _hash_alloc_buckets -- allocate a new splitpoint's worth of bucket pages * * This does not need to initialize the new bucket pages; we'll do that as * each one is used by _hash_expandtable(). But we have to extend the logical * EOF to the end of the splitpoint; this keeps smgr's idea of the EOF in * sync with ours, so that we don't get complaints from smgr. * * We do this by writing a page of zeroes at the end of the splitpoint range. * We expect that the filesystem will ensure that the intervening pages read * as zeroes too. On many filesystems this "hole" will not be allocated * immediately, which means that the index file may end up more fragmented * than if we forced it all to be allocated now; but since we don't scan * hash indexes sequentially anyway, that probably doesn't matter. * * XXX It's annoying that this code is executed with the metapage lock held. * We need to interlock against _hash_addovflpage() adding a new overflow page * concurrently, but it'd likely be better to use LockRelationForExtension * for the purpose. OTOH, adding a splitpoint is a very infrequent operation, * so it may not be worth worrying about. * * Returns true if successful, or false if allocation failed due to * BlockNumber overflow. */ static bool _hash_alloc_buckets(Relation rel, BlockNumber firstblock, uint32 nblocks) { BlockNumber lastblock; PGAlignedBlock zerobuf; Page page; HashPageOpaque ovflopaque; lastblock = firstblock + nblocks - 1; /* * Check for overflow in block number calculation; if so, we cannot extend * the index anymore. */ if (lastblock < firstblock || lastblock == InvalidBlockNumber) return false; page = (Page) zerobuf.data; /* * Initialize the page. Just zeroing the page won't work; see * _hash_freeovflpage for similar usage. We take care to make the special * space valid for the benefit of tools such as pageinspect. */ _hash_pageinit(page, BLCKSZ); ovflopaque = (HashPageOpaque) PageGetSpecialPointer(page); ovflopaque->hasho_prevblkno = InvalidBlockNumber; ovflopaque->hasho_nextblkno = InvalidBlockNumber; ovflopaque->hasho_bucket = -1; ovflopaque->hasho_flag = LH_UNUSED_PAGE; ovflopaque->hasho_page_id = HASHO_PAGE_ID; if (RelationNeedsWAL(rel)) log_newpage(&rel->rd_node, MAIN_FORKNUM, lastblock, zerobuf.data, true); RelationOpenSmgr(rel); PageSetChecksumInplace(page, lastblock); smgrextend(rel->rd_smgr, MAIN_FORKNUM, lastblock, zerobuf.data, false); return true; } /* * _hash_splitbucket -- split 'obucket' into 'obucket' and 'nbucket' * * This routine is used to partition the tuples between old and new bucket and * is used to finish the incomplete split operations. To finish the previously * interrupted split operation, the caller needs to fill htab. If htab is set, * then we skip the movement of tuples that exists in htab, otherwise NULL * value of htab indicates movement of all the tuples that belong to the new * bucket. * * We are splitting a bucket that consists of a base bucket page and zero * or more overflow (bucket chain) pages. We must relocate tuples that * belong in the new bucket. * * The caller must hold cleanup locks on both buckets to ensure that * no one else is trying to access them (see README). * * The caller must hold a pin, but no lock, on the metapage buffer. * The buffer is returned in the same state. (The metapage is only * touched if it becomes necessary to add or remove overflow pages.) * * Split needs to retain pin on primary bucket pages of both old and new * buckets till end of operation. This is to prevent vacuum from starting * while a split is in progress. * * In addition, the caller must have created the new bucket's base page, * which is passed in buffer nbuf, pinned and write-locked. The lock will be * released here and pin must be released by the caller. (The API is set up * this way because we must do _hash_getnewbuf() before releasing the metapage * write lock. So instead of passing the new bucket's start block number, we * pass an actual buffer.) */ static void _hash_splitbucket(Relation rel, Buffer metabuf, Bucket obucket, Bucket nbucket, Buffer obuf, Buffer nbuf, HTAB *htab, uint32 maxbucket, uint32 highmask, uint32 lowmask) { Buffer bucket_obuf; Buffer bucket_nbuf; Page opage; Page npage; HashPageOpaque oopaque; HashPageOpaque nopaque; OffsetNumber itup_offsets[MaxIndexTuplesPerPage]; IndexTuple itups[MaxIndexTuplesPerPage]; Size all_tups_size = 0; int i; uint16 nitups = 0; bucket_obuf = obuf; opage = BufferGetPage(obuf); oopaque = (HashPageOpaque) PageGetSpecialPointer(opage); bucket_nbuf = nbuf; npage = BufferGetPage(nbuf); nopaque = (HashPageOpaque) PageGetSpecialPointer(npage); /* Copy the predicate locks from old bucket to new bucket. */ PredicateLockPageSplit(rel, BufferGetBlockNumber(bucket_obuf), BufferGetBlockNumber(bucket_nbuf)); /* * Partition the tuples in the old bucket between the old bucket and the * new bucket, advancing along the old bucket's overflow bucket chain and * adding overflow pages to the new bucket as needed. Outer loop iterates * once per page in old bucket. */ for (;;) { BlockNumber oblkno; OffsetNumber ooffnum; OffsetNumber omaxoffnum; /* Scan each tuple in old page */ omaxoffnum = PageGetMaxOffsetNumber(opage); for (ooffnum = FirstOffsetNumber; ooffnum <= omaxoffnum; ooffnum = OffsetNumberNext(ooffnum)) { IndexTuple itup; Size itemsz; Bucket bucket; bool found = false; /* skip dead tuples */ if (ItemIdIsDead(PageGetItemId(opage, ooffnum))) continue; /* * Before inserting a tuple, probe the hash table containing TIDs * of tuples belonging to new bucket, if we find a match, then * skip that tuple, else fetch the item's hash key (conveniently * stored in the item) and determine which bucket it now belongs * in. */ itup = (IndexTuple) PageGetItem(opage, PageGetItemId(opage, ooffnum)); if (htab) (void) hash_search(htab, &itup->t_tid, HASH_FIND, &found); if (found) continue; bucket = _hash_hashkey2bucket(_hash_get_indextuple_hashkey(itup), maxbucket, highmask, lowmask); if (bucket == nbucket) { IndexTuple new_itup; /* * make a copy of index tuple as we have to scribble on it. */ new_itup = CopyIndexTuple(itup); /* * mark the index tuple as moved by split, such tuples are * skipped by scan if there is split in progress for a bucket. */ new_itup->t_info |= INDEX_MOVED_BY_SPLIT_MASK; /* * insert the tuple into the new bucket. if it doesn't fit on * the current page in the new bucket, we must allocate a new * overflow page and place the tuple on that page instead. */ itemsz = IndexTupleSize(new_itup); itemsz = MAXALIGN(itemsz); if (PageGetFreeSpaceForMultipleTuples(npage, nitups + 1) < (all_tups_size + itemsz)) { /* * Change the shared buffer state in critical section, * otherwise any error could make it unrecoverable. */ START_CRIT_SECTION(); _hash_pgaddmultitup(rel, nbuf, itups, itup_offsets, nitups); MarkBufferDirty(nbuf); /* log the split operation before releasing the lock */ log_split_page(rel, nbuf); END_CRIT_SECTION(); /* drop lock, but keep pin */ LockBuffer(nbuf, BUFFER_LOCK_UNLOCK); /* be tidy */ for (i = 0; i < nitups; i++) pfree(itups[i]); nitups = 0; all_tups_size = 0; /* chain to a new overflow page */ nbuf = _hash_addovflpage(rel, metabuf, nbuf, (nbuf == bucket_nbuf) ? true : false); npage = BufferGetPage(nbuf); nopaque = (HashPageOpaque) PageGetSpecialPointer(npage); } itups[nitups++] = new_itup; all_tups_size += itemsz; } else { /* * the tuple stays on this page, so nothing to do. */ Assert(bucket == obucket); } } oblkno = oopaque->hasho_nextblkno; /* retain the pin on the old primary bucket */ if (obuf == bucket_obuf) LockBuffer(obuf, BUFFER_LOCK_UNLOCK); else _hash_relbuf(rel, obuf); /* Exit loop if no more overflow pages in old bucket */ if (!BlockNumberIsValid(oblkno)) { /* * Change the shared buffer state in critical section, otherwise * any error could make it unrecoverable. */ START_CRIT_SECTION(); _hash_pgaddmultitup(rel, nbuf, itups, itup_offsets, nitups); MarkBufferDirty(nbuf); /* log the split operation before releasing the lock */ log_split_page(rel, nbuf); END_CRIT_SECTION(); if (nbuf == bucket_nbuf) LockBuffer(nbuf, BUFFER_LOCK_UNLOCK); else _hash_relbuf(rel, nbuf); /* be tidy */ for (i = 0; i < nitups; i++) pfree(itups[i]); break; } /* Else, advance to next old page */ obuf = _hash_getbuf(rel, oblkno, HASH_READ, LH_OVERFLOW_PAGE); opage = BufferGetPage(obuf); oopaque = (HashPageOpaque) PageGetSpecialPointer(opage); } /* * We're at the end of the old bucket chain, so we're done partitioning * the tuples. Mark the old and new buckets to indicate split is * finished. * * To avoid deadlocks due to locking order of buckets, first lock the old * bucket and then the new bucket. */ LockBuffer(bucket_obuf, BUFFER_LOCK_EXCLUSIVE); opage = BufferGetPage(bucket_obuf); oopaque = (HashPageOpaque) PageGetSpecialPointer(opage); LockBuffer(bucket_nbuf, BUFFER_LOCK_EXCLUSIVE); npage = BufferGetPage(bucket_nbuf); nopaque = (HashPageOpaque) PageGetSpecialPointer(npage); START_CRIT_SECTION(); oopaque->hasho_flag &= ~LH_BUCKET_BEING_SPLIT; nopaque->hasho_flag &= ~LH_BUCKET_BEING_POPULATED; /* * After the split is finished, mark the old bucket to indicate that it * contains deletable tuples. We will clear split-cleanup flag after * deleting such tuples either at the end of split or at the next split * from old bucket or at the time of vacuum. */ oopaque->hasho_flag |= LH_BUCKET_NEEDS_SPLIT_CLEANUP; /* * now write the buffers, here we don't release the locks as caller is * responsible to release locks. */ MarkBufferDirty(bucket_obuf); MarkBufferDirty(bucket_nbuf); if (RelationNeedsWAL(rel)) { XLogRecPtr recptr; xl_hash_split_complete xlrec; xlrec.old_bucket_flag = oopaque->hasho_flag; xlrec.new_bucket_flag = nopaque->hasho_flag; XLogBeginInsert(); XLogRegisterData((char *) &xlrec, SizeOfHashSplitComplete); XLogRegisterBuffer(0, bucket_obuf, REGBUF_STANDARD); XLogRegisterBuffer(1, bucket_nbuf, REGBUF_STANDARD); recptr = XLogInsert(RM_HASH_ID, XLOG_HASH_SPLIT_COMPLETE); PageSetLSN(BufferGetPage(bucket_obuf), recptr); PageSetLSN(BufferGetPage(bucket_nbuf), recptr); } END_CRIT_SECTION(); /* * If possible, clean up the old bucket. We might not be able to do this * if someone else has a pin on it, but if not then we can go ahead. This * isn't absolutely necessary, but it reduces bloat; if we don't do it * now, VACUUM will do it eventually, but maybe not until new overflow * pages have been allocated. Note that there's no need to clean up the * new bucket. */ if (IsBufferCleanupOK(bucket_obuf)) { LockBuffer(bucket_nbuf, BUFFER_LOCK_UNLOCK); hashbucketcleanup(rel, obucket, bucket_obuf, BufferGetBlockNumber(bucket_obuf), NULL, maxbucket, highmask, lowmask, NULL, NULL, true, NULL, NULL); } else { LockBuffer(bucket_nbuf, BUFFER_LOCK_UNLOCK); LockBuffer(bucket_obuf, BUFFER_LOCK_UNLOCK); } } /* * _hash_finish_split() -- Finish the previously interrupted split operation * * To complete the split operation, we form the hash table of TIDs in new * bucket which is then used by split operation to skip tuples that are * already moved before the split operation was previously interrupted. * * The caller must hold a pin, but no lock, on the metapage and old bucket's * primary page buffer. The buffers are returned in the same state. (The * metapage is only touched if it becomes necessary to add or remove overflow * pages.) */ void _hash_finish_split(Relation rel, Buffer metabuf, Buffer obuf, Bucket obucket, uint32 maxbucket, uint32 highmask, uint32 lowmask) { HASHCTL hash_ctl; HTAB *tidhtab; Buffer bucket_nbuf = InvalidBuffer; Buffer nbuf; Page npage; BlockNumber nblkno; BlockNumber bucket_nblkno; HashPageOpaque npageopaque; Bucket nbucket; bool found; /* Initialize hash tables used to track TIDs */ memset(&hash_ctl, 0, sizeof(hash_ctl)); hash_ctl.keysize = sizeof(ItemPointerData); hash_ctl.entrysize = sizeof(ItemPointerData); hash_ctl.hcxt = CurrentMemoryContext; tidhtab = hash_create("bucket ctids", 256, /* arbitrary initial size */ &hash_ctl, HASH_ELEM | HASH_BLOBS | HASH_CONTEXT); bucket_nblkno = nblkno = _hash_get_newblock_from_oldbucket(rel, obucket); /* * Scan the new bucket and build hash table of TIDs */ for (;;) { OffsetNumber noffnum; OffsetNumber nmaxoffnum; nbuf = _hash_getbuf(rel, nblkno, HASH_READ, LH_BUCKET_PAGE | LH_OVERFLOW_PAGE); /* remember the primary bucket buffer to acquire cleanup lock on it. */ if (nblkno == bucket_nblkno) bucket_nbuf = nbuf; npage = BufferGetPage(nbuf); npageopaque = (HashPageOpaque) PageGetSpecialPointer(npage); /* Scan each tuple in new page */ nmaxoffnum = PageGetMaxOffsetNumber(npage); for (noffnum = FirstOffsetNumber; noffnum <= nmaxoffnum; noffnum = OffsetNumberNext(noffnum)) { IndexTuple itup; /* Fetch the item's TID and insert it in hash table. */ itup = (IndexTuple) PageGetItem(npage, PageGetItemId(npage, noffnum)); (void) hash_search(tidhtab, &itup->t_tid, HASH_ENTER, &found); Assert(!found); } nblkno = npageopaque->hasho_nextblkno; /* * release our write lock without modifying buffer and ensure to * retain the pin on primary bucket. */ if (nbuf == bucket_nbuf) LockBuffer(nbuf, BUFFER_LOCK_UNLOCK); else _hash_relbuf(rel, nbuf); /* Exit loop if no more overflow pages in new bucket */ if (!BlockNumberIsValid(nblkno)) break; } /* * Conditionally get the cleanup lock on old and new buckets to perform * the split operation. If we don't get the cleanup locks, silently give * up and next insertion on old bucket will try again to complete the * split. */ if (!ConditionalLockBufferForCleanup(obuf)) { hash_destroy(tidhtab); return; } if (!ConditionalLockBufferForCleanup(bucket_nbuf)) { LockBuffer(obuf, BUFFER_LOCK_UNLOCK); hash_destroy(tidhtab); return; } npage = BufferGetPage(bucket_nbuf); npageopaque = (HashPageOpaque) PageGetSpecialPointer(npage); nbucket = npageopaque->hasho_bucket; _hash_splitbucket(rel, metabuf, obucket, nbucket, obuf, bucket_nbuf, tidhtab, maxbucket, highmask, lowmask); _hash_dropbuf(rel, bucket_nbuf); hash_destroy(tidhtab); } /* * log_split_page() -- Log the split operation * * We log the split operation when the new page in new bucket gets full, * so we log the entire page. * * 'buf' must be locked by the caller which is also responsible for unlocking * it. */ static void log_split_page(Relation rel, Buffer buf) { if (RelationNeedsWAL(rel)) { XLogRecPtr recptr; XLogBeginInsert(); XLogRegisterBuffer(0, buf, REGBUF_FORCE_IMAGE | REGBUF_STANDARD); recptr = XLogInsert(RM_HASH_ID, XLOG_HASH_SPLIT_PAGE); PageSetLSN(BufferGetPage(buf), recptr); } } /* * _hash_getcachedmetap() -- Returns cached metapage data. * * If metabuf is not InvalidBuffer, caller must hold a pin, but no lock, on * the metapage. If not set, we'll set it before returning if we have to * refresh the cache, and return with a pin but no lock on it; caller is * responsible for releasing the pin. * * We refresh the cache if it's not initialized yet or force_refresh is true. */ HashMetaPage _hash_getcachedmetap(Relation rel, Buffer *metabuf, bool force_refresh) { Page page; Assert(metabuf); if (force_refresh || rel->rd_amcache == NULL) { char *cache = NULL; /* * It's important that we don't set rd_amcache to an invalid value. * Either MemoryContextAlloc or _hash_getbuf could fail, so don't * install a pointer to the newly-allocated storage in the actual * relcache entry until both have succeeded. */ if (rel->rd_amcache == NULL) cache = MemoryContextAlloc(rel->rd_indexcxt, sizeof(HashMetaPageData)); /* Read the metapage. */ if (BufferIsValid(*metabuf)) LockBuffer(*metabuf, BUFFER_LOCK_SHARE); else *metabuf = _hash_getbuf(rel, HASH_METAPAGE, HASH_READ, LH_META_PAGE); page = BufferGetPage(*metabuf); /* Populate the cache. */ if (rel->rd_amcache == NULL) rel->rd_amcache = cache; memcpy(rel->rd_amcache, HashPageGetMeta(page), sizeof(HashMetaPageData)); /* Release metapage lock, but keep the pin. */ LockBuffer(*metabuf, BUFFER_LOCK_UNLOCK); } return (HashMetaPage) rel->rd_amcache; } /* * _hash_getbucketbuf_from_hashkey() -- Get the bucket's buffer for the given * hashkey. * * Bucket pages do not move or get removed once they are allocated. This give * us an opportunity to use the previously saved metapage contents to reach * the target bucket buffer, instead of reading from the metapage every time. * This saves one buffer access every time we want to reach the target bucket * buffer, which is very helpful savings in bufmgr traffic and contention. * * The access type parameter (HASH_READ or HASH_WRITE) indicates whether the * bucket buffer has to be locked for reading or writing. * * The out parameter cachedmetap is set with metapage contents used for * hashkey to bucket buffer mapping. Some callers need this info to reach the * old bucket in case of bucket split, see _hash_doinsert(). */ Buffer _hash_getbucketbuf_from_hashkey(Relation rel, uint32 hashkey, int access, HashMetaPage *cachedmetap) { HashMetaPage metap; Buffer buf; Buffer metabuf = InvalidBuffer; Page page; Bucket bucket; BlockNumber blkno; HashPageOpaque opaque; /* We read from target bucket buffer, hence locking is must. */ Assert(access == HASH_READ || access == HASH_WRITE); metap = _hash_getcachedmetap(rel, &metabuf, false); Assert(metap != NULL); /* * Loop until we get a lock on the correct target bucket. */ for (;;) { /* * Compute the target bucket number, and convert to block number. */ bucket = _hash_hashkey2bucket(hashkey, metap->hashm_maxbucket, metap->hashm_highmask, metap->hashm_lowmask); blkno = BUCKET_TO_BLKNO(metap, bucket); /* Fetch the primary bucket page for the bucket */ buf = _hash_getbuf(rel, blkno, access, LH_BUCKET_PAGE); page = BufferGetPage(buf); opaque = (HashPageOpaque) PageGetSpecialPointer(page); Assert(opaque->hasho_bucket == bucket); Assert(opaque->hasho_prevblkno != InvalidBlockNumber); /* * If this bucket hasn't been split, we're done. */ if (opaque->hasho_prevblkno <= metap->hashm_maxbucket) break; /* Drop lock on this buffer, update cached metapage, and retry. */ _hash_relbuf(rel, buf); metap = _hash_getcachedmetap(rel, &metabuf, true); Assert(metap != NULL); } if (BufferIsValid(metabuf)) _hash_dropbuf(rel, metabuf); if (cachedmetap) *cachedmetap = metap; return buf; }