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Diffstat (limited to 'src/backend/access/hash/hashpage.c')
| -rw-r--r-- | src/backend/access/hash/hashpage.c | 1617 |
1 files changed, 1617 insertions, 0 deletions
diff --git a/src/backend/access/hash/hashpage.c b/src/backend/access/hash/hashpage.c new file mode 100644 index 0000000..9da5fb4 --- /dev/null +++ b/src/backend/access/hash/hashpage.c @@ -0,0 +1,1617 @@ +/*------------------------------------------------------------------------- + * + * hashpage.c + * Hash table page management code for the Postgres hash access method + * + * Portions Copyright (c) 1996-2022, 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 "access/xloginsert.h" +#include "miscadmin.h" +#include "port/pg_bitutils.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 = HashPageGetOpaque(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 = HashGetTargetPageUsage(rel) / 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 lshift; + + /* + * 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 = HashPageGetOpaque(page); + pageopaque->hasho_prevblkno = InvalidBlockNumber; + pageopaque->hasho_nextblkno = InvalidBlockNumber; + pageopaque->hasho_bucket = InvalidBucket; + 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 */ + lshift = pg_leftmost_one_pos32(metap->hashm_bsize); + Assert(lshift > 0); + metap->hashm_bmsize = 1 << lshift; + metap->hashm_bmshift = lshift + 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 = pg_nextpower2_32(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 to prevent failure of pg_ceil_log2_32() 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 = HashPageGetOpaque(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. + * + * XXX It doesn't make sense to call _hash_getnewbuf first, zeroing the + * buffer, and then only afterwards check whether we have a cleanup lock. + * However, since no scan can be accessing the buffer yet, any concurrent + * accesses will just be from processes like the bgwriter or checkpointer + * which don't care about its contents, so it doesn't really matter. + */ + 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 = HashPageGetOpaque(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 = HashPageGetOpaque(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 = HashPageGetOpaque(page); + + ovflopaque->hasho_prevblkno = InvalidBlockNumber; + ovflopaque->hasho_nextblkno = InvalidBlockNumber; + ovflopaque->hasho_bucket = InvalidBucket; + 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); + + PageSetChecksumInplace(page, lastblock); + smgrextend(RelationGetSmgr(rel), 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 = HashPageGetOpaque(opage); + + bucket_nbuf = nbuf; + npage = BufferGetPage(nbuf); + nopaque = HashPageGetOpaque(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)); + npage = BufferGetPage(nbuf); + nopaque = HashPageGetOpaque(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 = HashPageGetOpaque(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 = HashPageGetOpaque(opage); + + LockBuffer(bucket_nbuf, BUFFER_LOCK_EXCLUSIVE); + npage = BufferGetPage(bucket_nbuf); + nopaque = HashPageGetOpaque(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 */ + 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 = HashPageGetOpaque(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 = HashPageGetOpaque(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 = HashPageGetOpaque(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; +} |