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Commit385cbe8

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Handle new HOT chains in index-build table scans
When a table is scanned by heapam_index_build_range_scan (néeIndexBuildHeapScan) and the table lock being held allows concurrent datachanges, it is possible for new HOT chains to sprout in a page that wereunknown when the scan of a page happened. This leads to an error suchas ERROR: failed to find parent tuple for heap-only tuple at (X,Y) in table "tbl"because the root tuple was not present when we first obtained the listof the page's root tuples. This can be fixed by re-obtaining the listof root tuples, if we see that a heap-only tuple appears to point to anon-existing root.This was reported by Anastasia as occurring for BRIN summarization(which exists since 9.5), but I think it could theoretically also happenwith CREATE INDEX CONCURRENTLY (much older) or REINDEX CONCURRENTLY(very recent). It seems a happy coincidence that BRIN forces us tobackpatch this all the way to 9.5.Reported-by: Anastasia Lubennikova <a.lubennikova@postgrespro.ru>Diagnosed-by: Anastasia Lubennikova <a.lubennikova@postgrespro.ru>Co-authored-by: Anastasia Lubennikova <a.lubennikova@postgrespro.ru>Co-authored-by: Álvaro Herrera <alvherre@alvh.no-ip.org>Discussion:https://postgr.es/m/602d8487-f0b2-5486-0088-0f372b2549fa@postgrespro.ruBackpatch: 9.5 - master
1 parent721ef4d commit385cbe8

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2 files changed

+23
-2
lines changed

2 files changed

+23
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lines changed

‎src/backend/access/heap/pruneheap.c

Lines changed: 3 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -730,7 +730,7 @@ heap_page_prune_execute(Buffer buffer,
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* root_offsets[k - 1] = j.
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*
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* The passed-in root_offsets array must have MaxHeapTuplesPerPage entries.
733-
*We zero out all unused entries.
733+
*Unused entries are filled with InvalidOffsetNumber (zero).
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*
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* The function must be called with at least share lock on the buffer, to
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* prevent concurrent prune operations.
@@ -745,7 +745,8 @@ heap_get_root_tuples(Page page, OffsetNumber *root_offsets)
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OffsetNumberoffnum,
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maxoff;
747747

748-
MemSet(root_offsets,0,MaxHeapTuplesPerPage*sizeof(OffsetNumber));
748+
MemSet(root_offsets,InvalidOffsetNumber,
749+
MaxHeapTuplesPerPage*sizeof(OffsetNumber));
749750

750751
maxoff=PageGetMaxOffsetNumber(page);
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for (offnum=FirstOffsetNumber;offnum <=maxoff;offnum=OffsetNumberNext(offnum))

‎src/backend/catalog/index.c

Lines changed: 20 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -2409,6 +2409,12 @@ IndexBuildHeapRangeScan(Relation heapRelation,
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* buffer continuously while visiting the page, so no pruning
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* operation can occur either.
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*
2412+
* In cases with only ShareUpdateExclusiveLock on the table, it's
2413+
* possible for some HOT tuples to appear that we didn't know about
2414+
* when we first read the page. To handle that case, we re-obtain the
2415+
* list of root offsets when a HOT tuple points to a root item that we
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* don't know about.
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*
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* Also, although our opinions about tuple liveness could change while
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* we scan the page (due to concurrent transaction commits/aborts),
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* the chain root locations won't, so this info doesn't need to be
@@ -2679,6 +2685,20 @@ IndexBuildHeapRangeScan(Relation heapRelation,
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rootTuple=*heapTuple;
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offnum=ItemPointerGetOffsetNumber(&heapTuple->t_self);
26812687

2688+
/*
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* If a HOT tuple points to a root that we don't know
2690+
* about, obtain root items afresh. If that still fails,
2691+
* report it as corruption.
2692+
*/
2693+
if (root_offsets[offnum-1]==InvalidOffsetNumber)
2694+
{
2695+
Pagepage=BufferGetPage(scan->rs_cbuf);
2696+
2697+
LockBuffer(scan->rs_cbuf,BUFFER_LOCK_SHARE);
2698+
heap_get_root_tuples(page,root_offsets);
2699+
LockBuffer(scan->rs_cbuf,BUFFER_LOCK_UNLOCK);
2700+
}
2701+
26822702
if (!OffsetNumberIsValid(root_offsets[offnum-1]))
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ereport(ERROR,
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(errcode(ERRCODE_DATA_CORRUPTED),

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