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Commitb508a56

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Predicate locking in hash indexes.
Hash index searches acquire predicate locks on the primarypage of a bucket. It acquires a lock on both the old and new bucketsfor scans that happen concurrently with page splits. During a bucketsplit, a predicate lock is copied from the primary page of an oldbucket to the primary page of a new bucket.Author: Shubham Barai, Amit KapilaReviewed by: Amit Kapila, Alexander Korotkov, Thomas MunroDiscussion:https://www.postgresql.org/message-id/flat/CALxAEPvNsM2GTiXdRgaaZ1Pjd1bs+sxfFsf7Ytr+iq+5JJoYXA@mail.gmail.com
1 parent971d7dd commitb508a56

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8 files changed

+802
-1
lines changed

8 files changed

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‎src/backend/access/hash/hash.c

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -68,7 +68,7 @@ hashhandler(PG_FUNCTION_ARGS)
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amroutine->amsearchnulls= false;
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amroutine->amstorage= false;
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amroutine->amclusterable= false;
71-
amroutine->ampredlocks=false;
71+
amroutine->ampredlocks=true;
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amroutine->amcanparallel= false;
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amroutine->amkeytype=INT4OID;
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‎src/backend/access/hash/hashinsert.c

Lines changed: 3 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -22,6 +22,7 @@
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#include"utils/rel.h"
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#include"storage/lwlock.h"
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#include"storage/buf_internals.h"
25+
#include"storage/predicate.h"
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2627
staticvoid_hash_vacuum_one_page(Relationrel,Buffermetabuf,Bufferbuf,
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RelFileNodehnode);
@@ -88,6 +89,8 @@ _hash_doinsert(Relation rel, IndexTuple itup, Relation heapRel)
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&usedmetap);
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Assert(usedmetap!=NULL);
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CheckForSerializableConflictIn(rel,NULL,buf);
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/* remember the primary bucket buffer to release the pin on it at end. */
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bucket_buf=buf;
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‎src/backend/access/hash/hashpage.c

Lines changed: 6 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -33,6 +33,7 @@
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#include"miscadmin.h"
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#include"storage/lmgr.h"
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#include"storage/smgr.h"
36+
#include"storage/predicate.h"
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staticbool_hash_alloc_buckets(Relationrel,BlockNumberfirstblock,
@@ -1107,6 +1108,11 @@ _hash_splitbucket(Relation rel,
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npage=BufferGetPage(nbuf);
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nopaque= (HashPageOpaque)PageGetSpecialPointer(npage);
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1111+
/* Copy the predicate locks from old bucket to new bucket. */
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PredicateLockPageSplit(rel,
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BufferGetBlockNumber(bucket_obuf),
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BufferGetBlockNumber(bucket_nbuf));
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/*
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* Partition the tuples in the old bucket between the old bucket and the
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* new bucket, advancing along the old bucket's overflow bucket chain and

‎src/backend/access/hash/hashsearch.c

Lines changed: 3 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -19,6 +19,7 @@
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#include"miscadmin.h"
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#include"pgstat.h"
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#include"utils/rel.h"
22+
#include"storage/predicate.h"
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staticbool_hash_readpage(IndexScanDescscan,Buffer*bufP,
2425
ScanDirectiondir);
@@ -171,6 +172,7 @@ _hash_readnext(IndexScanDesc scan,
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Assert(BufferIsValid(*bufp));
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173174
LockBuffer(*bufp,BUFFER_LOCK_SHARE);
175+
PredicateLockPage(rel,BufferGetBlockNumber(*bufp),scan->xs_snapshot);
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175177
/*
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* setting hashso_buc_split to true indicates that we are scanning
@@ -347,6 +349,7 @@ _hash_first(IndexScanDesc scan, ScanDirection dir)
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so->hashso_sk_hash=hashkey;
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buf=_hash_getbucketbuf_from_hashkey(rel,hashkey,HASH_READ,NULL);
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PredicateLockPage(rel,BufferGetBlockNumber(buf),scan->xs_snapshot);
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page=BufferGetPage(buf);
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TestForOldSnapshot(scan->xs_snapshot,rel,page);
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opaque= (HashPageOpaque)PageGetSpecialPointer(page);

‎src/backend/storage/lmgr/README-SSI

Lines changed: 7 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -389,6 +389,13 @@ relation is required. Fast update postpones the insertion of tuples into index
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structure by temporarily storing them into pending list. That makes us unable
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to detect r-w conflicts using page-level locks.
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* Hash index searches acquire predicate locks on the primary
393+
page of a bucket. It acquires a lock on both the old and new buckets
394+
for scans that happen concurrently with page splits. During a bucket
395+
split, a predicate lock is copied from the primary page of an old
396+
bucket to the primary page of a new bucket.
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398+
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* The effects of page splits, overflows, consolidations, and
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removals must be carefully reviewed to ensure that predicate locks
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aren't "lost" during those operations, or kept with pages which could

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