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Fix systable_recheck_tuple() for MVCC scan snapshots.

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Since this function assumed non-MVCC snapshots, it broke when commit
568d4138c646cd7cd8a837ac244ef2caf27c6bb8 switched its one caller from
SnapshotNow scans to MVCC-snapshot scans.

Reviewed by Robert Haas, Tom Lane and Andres Freund.
This commit is contained in:
Noah Misch 2013-07-16 20:16:32 -04:00
parent b560ec1b0d
commit ffcf654547
1 changed files with 16 additions and 4 deletions
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20
src/backend/access/index/genam.c
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@ -361,6 +361,10 @@ systable_getnext(SysScanDesc sysscan)
/* /*
* systable_recheck_tuple --- recheck visibility of most-recently-fetched tuple * systable_recheck_tuple --- recheck visibility of most-recently-fetched tuple
* *
* In particular, determine if this tuple would be visible to a catalog scan
* that started now. We don't handle the case of a non-MVCC scan snapshot,
* because no caller needs that yet.
*
* This is useful to test whether an object was deleted while we waited to * This is useful to test whether an object was deleted while we waited to
* acquire lock on it. * acquire lock on it.
* *
@ -370,30 +374,38 @@ systable_getnext(SysScanDesc sysscan)
bool bool
systable_recheck_tuple(SysScanDesc sysscan, HeapTuple tup) systable_recheck_tuple(SysScanDesc sysscan, HeapTuple tup)
{ {
Snapshot freshsnap;
bool result; bool result;
/*
* Trust that LockBuffer() and HeapTupleSatisfiesMVCC() do not themselves
* acquire snapshots, so we need not register the snapshot. Those
* facilities are too low-level to have any business scanning tables.
*/
freshsnap = GetCatalogSnapshot(RelationGetRelid(sysscan->heap_rel));
if (sysscan->irel) if (sysscan->irel)
{ {
IndexScanDesc scan = sysscan->iscan; IndexScanDesc scan = sysscan->iscan;
Assert(IsMVCCSnapshot(scan->xs_snapshot));
Assert(tup == &scan->xs_ctup); Assert(tup == &scan->xs_ctup);
Assert(BufferIsValid(scan->xs_cbuf)); Assert(BufferIsValid(scan->xs_cbuf));
/* must hold a buffer lock to call HeapTupleSatisfiesVisibility */ /* must hold a buffer lock to call HeapTupleSatisfiesVisibility */
LockBuffer(scan->xs_cbuf, BUFFER_LOCK_SHARE); LockBuffer(scan->xs_cbuf, BUFFER_LOCK_SHARE);
result = HeapTupleSatisfiesVisibility(tup, scan->xs_snapshot, result = HeapTupleSatisfiesVisibility(tup, freshsnap, scan->xs_cbuf);
scan->xs_cbuf);
LockBuffer(scan->xs_cbuf, BUFFER_LOCK_UNLOCK); LockBuffer(scan->xs_cbuf, BUFFER_LOCK_UNLOCK);
} }
else else
{ {
HeapScanDesc scan = sysscan->scan; HeapScanDesc scan = sysscan->scan;
Assert(IsMVCCSnapshot(scan->rs_snapshot));
Assert(tup == &scan->rs_ctup); Assert(tup == &scan->rs_ctup);
Assert(BufferIsValid(scan->rs_cbuf)); Assert(BufferIsValid(scan->rs_cbuf));
/* must hold a buffer lock to call HeapTupleSatisfiesVisibility */ /* must hold a buffer lock to call HeapTupleSatisfiesVisibility */
LockBuffer(scan->rs_cbuf, BUFFER_LOCK_SHARE); LockBuffer(scan->rs_cbuf, BUFFER_LOCK_SHARE);
result = HeapTupleSatisfiesVisibility(tup, scan->rs_snapshot, result = HeapTupleSatisfiesVisibility(tup, freshsnap, scan->rs_cbuf);
scan->rs_cbuf);
LockBuffer(scan->rs_cbuf, BUFFER_LOCK_UNLOCK); LockBuffer(scan->rs_cbuf, BUFFER_LOCK_UNLOCK);
} }
return result; return result;