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Commit9a10945

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Fix bugs in contrib/pg_visibility.
collect_corrupt_items() failed to initialize tuple.t_self. WhileHeapTupleSatisfiesVacuum() doesn't actually use that value, it doesAssert that it's valid, so that the code would dump core if ip_posidchanced to be zero. (That's somewhat unlikely, which probably explainshow this got missed. In any case it wouldn't matter for field use.)Also, collect_corrupt_items was returning the wrong TIDs, that is thecontents of t_ctid rather than the tuple's own location. This wouldbe the same thing in simple cases, but it could be wrong if, forexample, a past update attempt had been rolled back, leaving a livetuple whose t_ctid doesn't point at itself.Also, in pg_visibility(), guard against trying to read a page pastthe end of the rel. The VM code handles inquiries beyond the endof the map by silently returning zeroes, and it seems like we shoulddo the same thing here.I ran into the assertion failure while using pg_visibility to checkpg_upgrade's behavior, and then noted the other problems whilereading the code.Report: <29043.1475288648@sss.pgh.pa.us>
1 parent33596ed commit9a10945

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-12
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1 file changed

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‎contrib/pg_visibility/pg_visibility.c

Lines changed: 26 additions & 12 deletions
Original file line numberDiff line numberDiff line change
@@ -3,6 +3,8 @@
33
* pg_visibility.c
44
* display visibility map information and page-level visibility bits
55
*
6+
* Copyright (c) 2016, PostgreSQL Global Development Group
7+
*
68
* contrib/pg_visibility/pg_visibility.c
79
*-------------------------------------------------------------------------
810
*/
@@ -54,6 +56,10 @@ static bool tuple_all_visible(HeapTuple tup, TransactionId OldestXmin,
5456

5557
/*
5658
* Visibility map information for a single block of a relation.
59+
*
60+
* Note: the VM code will silently return zeroes for pages past the end
61+
* of the map, so we allow probes up to MaxBlockNumber regardless of the
62+
* actual relation size.
5763
*/
5864
Datum
5965
pg_visibility_map(PG_FUNCTION_ARGS)
@@ -122,13 +128,22 @@ pg_visibility(PG_FUNCTION_ARGS)
122128
values[0]=BoolGetDatum((mapbits&VISIBILITYMAP_ALL_VISIBLE)!=0);
123129
values[1]=BoolGetDatum((mapbits&VISIBILITYMAP_ALL_FROZEN)!=0);
124130

125-
buffer=ReadBuffer(rel,blkno);
126-
LockBuffer(buffer,BUFFER_LOCK_SHARE);
131+
/* Here we have to explicitly check rel size ... */
132+
if (blkno<RelationGetNumberOfBlocks(rel))
133+
{
134+
buffer=ReadBuffer(rel,blkno);
135+
LockBuffer(buffer,BUFFER_LOCK_SHARE);
127136

128-
page=BufferGetPage(buffer);
129-
values[2]=BoolGetDatum(PageIsAllVisible(page));
137+
page=BufferGetPage(buffer);
138+
values[2]=BoolGetDatum(PageIsAllVisible(page));
130139

131-
UnlockReleaseBuffer(buffer);
140+
UnlockReleaseBuffer(buffer);
141+
}
142+
else
143+
{
144+
/* As with the vismap, silently return 0 for pages past EOF */
145+
values[2]=BoolGetDatum(false);
146+
}
132147

133148
relation_close(rel,AccessShareLock);
134149

@@ -611,14 +626,13 @@ collect_corrupt_items(Oid relid, bool all_visible, bool all_frozen)
611626
/* Dead line pointers are neither all-visible nor frozen. */
612627
if (ItemIdIsDead(itemid))
613628
{
614-
ItemPointerDatatid;
615-
616-
ItemPointerSet(&tid,blkno,offnum);
617-
record_corrupt_item(items,&tid);
629+
ItemPointerSet(&(tuple.t_self),blkno,offnum);
630+
record_corrupt_item(items,&tuple.t_self);
618631
continue;
619632
}
620633

621634
/* Initialize a HeapTupleData structure for checks below. */
635+
ItemPointerSet(&(tuple.t_self),blkno,offnum);
622636
tuple.t_data= (HeapTupleHeader)PageGetItem(page,itemid);
623637
tuple.t_len=ItemIdGetLength(itemid);
624638
tuple.t_tableOid=relid;
@@ -649,12 +663,12 @@ collect_corrupt_items(Oid relid, bool all_visible, bool all_frozen)
649663
RecomputedOldestXmin=GetOldestXmin(NULL, true);
650664

651665
if (!TransactionIdPrecedes(OldestXmin,RecomputedOldestXmin))
652-
record_corrupt_item(items,&tuple.t_data->t_ctid);
666+
record_corrupt_item(items,&tuple.t_self);
653667
else
654668
{
655669
OldestXmin=RecomputedOldestXmin;
656670
if (!tuple_all_visible(&tuple,OldestXmin,buffer))
657-
record_corrupt_item(items,&tuple.t_data->t_ctid);
671+
record_corrupt_item(items,&tuple.t_self);
658672
}
659673
}
660674

@@ -665,7 +679,7 @@ collect_corrupt_items(Oid relid, bool all_visible, bool all_frozen)
665679
if (check_frozen)
666680
{
667681
if (heap_tuple_needs_eventual_freeze(tuple.t_data))
668-
record_corrupt_item(items,&tuple.t_data->t_ctid);
682+
record_corrupt_item(items,&tuple.t_self);
669683
}
670684
}
671685

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