/* * Bulk deletion of all index entries pointing to a set of heap tuples. * The set of target tuples is specified via a callback routine that tells * whether any given heap tuple (identified by ItemPointer) is being deleted. * * This function also deletes the tuples that are moved by split to other * bucket. * * Result: a palloc'd struct containing statistical info for VACUUM displays. */ IndexBulkDeleteResult * hashbulkdelete(IndexVacuumInfo *info, IndexBulkDeleteResult *stats, IndexBulkDeleteCallback callback, void *callback_state) { Relation rel = info->index; double tuples_removed; double num_index_tuples; double orig_ntuples; Bucket orig_maxbucket; Bucket cur_maxbucket; Bucket cur_bucket; Buffer metabuf = InvalidBuffer; HashMetaPage metap; HashMetaPage cachedmetap; tuples_removed = 0; num_index_tuples = 0; /* * We need a copy of the metapage so that we can use its hashm_spares[] * values to compute bucket page addresses, but a cached copy should be * good enough. (If not, we'll detect that further down and refresh the * cache as necessary.) */ cachedmetap = _hash_getcachedmetap(rel, &metabuf, false); Assert(cachedmetap != NULL); orig_maxbucket = cachedmetap->hashm_maxbucket; orig_ntuples = cachedmetap->hashm_ntuples; /* Scan the buckets that we know exist */ cur_bucket = 0; cur_maxbucket = orig_maxbucket; loop_top: while (cur_bucket <= cur_maxbucket) { BlockNumber bucket_blkno; BlockNumber blkno; Buffer bucket_buf; Buffer buf; HashPageOpaque bucket_opaque; Page page; bool split_cleanup = false; /* Get address of bucket's start page */ bucket_blkno = BUCKET_TO_BLKNO(cachedmetap, cur_bucket); blkno = bucket_blkno; /* * We need to acquire a cleanup lock on the primary bucket page to out * wait concurrent scans before deleting the dead tuples. */ buf = ReadBufferExtended(rel, MAIN_FORKNUM, blkno, RBM_NORMAL, info->strategy); LockBufferForCleanup(buf); _hash_checkpage(rel, buf, LH_BUCKET_PAGE); page = BufferGetPage(buf); bucket_opaque = (HashPageOpaque) PageGetSpecialPointer(page); /* * If the bucket contains tuples that are moved by split, then we need * to delete such tuples. We can't delete such tuples if the split * operation on bucket is not finished as those are needed by scans. */ if (!H_BUCKET_BEING_SPLIT(bucket_opaque) && H_NEEDS_SPLIT_CLEANUP(bucket_opaque)) { split_cleanup = true; /* * This bucket might have been split since we last held a lock on * the metapage. If so, hashm_maxbucket, hashm_highmask and * hashm_lowmask might be old enough to cause us to fail to remove * tuples left behind by the most recent split. To prevent that, * now that the primary page of the target bucket has been locked * (and thus can't be further split), check whether we need to * update our cached metapage data. */ Assert(bucket_opaque->hasho_prevblkno != InvalidBlockNumber); if (bucket_opaque->hasho_prevblkno > cachedmetap->hashm_maxbucket) { cachedmetap = _hash_getcachedmetap(rel, &metabuf, true); Assert(cachedmetap != NULL); } } bucket_buf = buf; hashbucketcleanup(rel, cur_bucket, bucket_buf, blkno, info->strategy, cachedmetap->hashm_maxbucket, cachedmetap->hashm_highmask, cachedmetap->hashm_lowmask, &tuples_removed, &num_index_tuples, split_cleanup, callback, callback_state); _hash_dropbuf(rel, bucket_buf); /* Advance to next bucket */ cur_bucket++; } if (BufferIsInvalid(metabuf)) metabuf = _hash_getbuf(rel, HASH_METAPAGE, HASH_NOLOCK, LH_META_PAGE); /* Write-lock metapage and check for split since we started */ LockBuffer(metabuf, BUFFER_LOCK_EXCLUSIVE); metap = HashPageGetMeta(BufferGetPage(metabuf)); if (cur_maxbucket != metap->hashm_maxbucket) { /* There's been a split, so process the additional bucket(s) */ LockBuffer(metabuf, BUFFER_LOCK_UNLOCK); cachedmetap = _hash_getcachedmetap(rel, &metabuf, true); Assert(cachedmetap != NULL); cur_maxbucket = cachedmetap->hashm_maxbucket; goto loop_top; } /* Okay, we're really done. Update tuple count in metapage. */ START_CRIT_SECTION(); if (orig_maxbucket == metap->hashm_maxbucket && orig_ntuples == metap->hashm_ntuples) { /* * No one has split or inserted anything since start of scan, so * believe our count as gospel. */ metap->hashm_ntuples = num_index_tuples; } else { /* * Otherwise, our count is untrustworthy since we may have * double-scanned tuples in split buckets. Proceed by dead-reckoning. * (Note: we still return estimated_count = false, because using this * count is better than not updating reltuples at all.) */ if (metap->hashm_ntuples > tuples_removed) metap->hashm_ntuples -= tuples_removed; else metap->hashm_ntuples = 0; num_index_tuples = metap->hashm_ntuples; } MarkBufferDirty(metabuf); /* XLOG stuff */ if (RelationNeedsWAL(rel)) { xl_hash_update_meta_page xlrec; XLogRecPtr recptr; xlrec.ntuples = metap->hashm_ntuples; XLogBeginInsert(); XLogRegisterData((char *) &xlrec, SizeOfHashUpdateMetaPage); XLogRegisterBuffer(0, metabuf, REGBUF_STANDARD); recptr = XLogInsert(RM_HASH_ID, XLOG_HASH_UPDATE_META_PAGE); PageSetLSN(BufferGetPage(metabuf), recptr); } END_CRIT_SECTION(); _hash_relbuf(rel, metabuf); /* return statistics */ if (stats == NULL) stats = (IndexBulkDeleteResult *) palloc0(sizeof(IndexBulkDeleteResult)); stats->estimated_count = false; stats->num_index_tuples = num_index_tuples; stats->tuples_removed += tuples_removed; /* hashvacuumcleanup will fill in num_pages */ return stats; }
/* * 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); }
/* * Bulk deletion of all index entries pointing to a set of heap tuples. * The set of target tuples is specified via a callback routine that tells * whether any given heap tuple (identified by ItemPointer) is being deleted. * * This function also deletes the tuples that are moved by split to other * bucket. * * Result: a palloc'd struct containing statistical info for VACUUM displays. */ IndexBulkDeleteResult * hashbulkdelete(IndexVacuumInfo *info, IndexBulkDeleteResult *stats, IndexBulkDeleteCallback callback, void *callback_state) { Relation rel = info->index; double tuples_removed; double num_index_tuples; double orig_ntuples; Bucket orig_maxbucket; Bucket cur_maxbucket; Bucket cur_bucket; Buffer metabuf; HashMetaPage metap; HashMetaPageData local_metapage; tuples_removed = 0; num_index_tuples = 0; /* * Read the metapage to fetch original bucket and tuple counts. Also, we * keep a copy of the last-seen metapage so that we can use its * hashm_spares[] values to compute bucket page addresses. This is a bit * hokey but perfectly safe, since the interesting entries in the spares * array cannot change under us; and it beats rereading the metapage for * each bucket. */ metabuf = _hash_getbuf(rel, HASH_METAPAGE, HASH_READ, LH_META_PAGE); metap = HashPageGetMeta(BufferGetPage(metabuf)); orig_maxbucket = metap->hashm_maxbucket; orig_ntuples = metap->hashm_ntuples; memcpy(&local_metapage, metap, sizeof(local_metapage)); _hash_relbuf(rel, metabuf); /* Scan the buckets that we know exist */ cur_bucket = 0; cur_maxbucket = orig_maxbucket; loop_top: while (cur_bucket <= cur_maxbucket) { BlockNumber bucket_blkno; BlockNumber blkno; Buffer bucket_buf; Buffer buf; HashPageOpaque bucket_opaque; Page page; bool split_cleanup = false; /* Get address of bucket's start page */ bucket_blkno = BUCKET_TO_BLKNO(&local_metapage, cur_bucket); blkno = bucket_blkno; /* * We need to acquire a cleanup lock on the primary bucket page to out * wait concurrent scans before deleting the dead tuples. */ buf = ReadBufferExtended(rel, MAIN_FORKNUM, blkno, RBM_NORMAL, info->strategy); LockBufferForCleanup(buf); _hash_checkpage(rel, buf, LH_BUCKET_PAGE); page = BufferGetPage(buf); bucket_opaque = (HashPageOpaque) PageGetSpecialPointer(page); /* * If the bucket contains tuples that are moved by split, then we need * to delete such tuples. We can't delete such tuples if the split * operation on bucket is not finished as those are needed by scans. */ if (!H_BUCKET_BEING_SPLIT(bucket_opaque) && H_NEEDS_SPLIT_CLEANUP(bucket_opaque)) split_cleanup = true; bucket_buf = buf; hashbucketcleanup(rel, cur_bucket, bucket_buf, blkno, info->strategy, local_metapage.hashm_maxbucket, local_metapage.hashm_highmask, local_metapage.hashm_lowmask, &tuples_removed, &num_index_tuples, split_cleanup, callback, callback_state); _hash_dropbuf(rel, bucket_buf); /* Advance to next bucket */ cur_bucket++; } /* Write-lock metapage and check for split since we started */ metabuf = _hash_getbuf(rel, HASH_METAPAGE, HASH_WRITE, LH_META_PAGE); metap = HashPageGetMeta(BufferGetPage(metabuf)); if (cur_maxbucket != metap->hashm_maxbucket) { /* There's been a split, so process the additional bucket(s) */ cur_maxbucket = metap->hashm_maxbucket; memcpy(&local_metapage, metap, sizeof(local_metapage)); _hash_relbuf(rel, metabuf); goto loop_top; } /* Okay, we're really done. Update tuple count in metapage. */ if (orig_maxbucket == metap->hashm_maxbucket && orig_ntuples == metap->hashm_ntuples) { /* * No one has split or inserted anything since start of scan, so * believe our count as gospel. */ metap->hashm_ntuples = num_index_tuples; } else { /* * Otherwise, our count is untrustworthy since we may have * double-scanned tuples in split buckets. Proceed by dead-reckoning. * (Note: we still return estimated_count = false, because using this * count is better than not updating reltuples at all.) */ if (metap->hashm_ntuples > tuples_removed) metap->hashm_ntuples -= tuples_removed; else metap->hashm_ntuples = 0; num_index_tuples = metap->hashm_ntuples; } _hash_wrtbuf(rel, metabuf); /* return statistics */ if (stats == NULL) stats = (IndexBulkDeleteResult *) palloc0(sizeof(IndexBulkDeleteResult)); stats->estimated_count = false; stats->num_index_tuples = num_index_tuples; stats->tuples_removed += tuples_removed; /* hashvacuumcleanup will fill in num_pages */ return stats; }
/* * _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); /* * 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 = IndexTupleDSize(*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); } }