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Commite1d6347

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committed
Don't mark pages all-visible spuriously
Dan Wood diagnosed a long-standing problem that pages containing tuplesthat are locked by multixacts containing live lockers may spuriously endup as candidates for getting their all-visible flag set. This has thelong-term effect that multixacts remain unfrozen; this may previouslypass undetected, but since commit XYZ it would be reported as "ERROR: found multixact 134100944 from before relminmxid 192042633"because when a later vacuum tries to freeze the page it detects that amultixact that should have gotten frozen, wasn't.Dan proposed a (correct) patch that simply sets a variable to itscorrect value, after a bogus initialization. But, per discussion, itseems better coding to avoid the bogus initializations altogether, sincethey could give rise to more bugs later. Therefore this fix rewritesthe logic a little bit to avoid depending on the bogus initializations.This bug was part of a family introduced in 9.6 by commita892234;later, commit38e9f90 fixed most of them, but this one wasunnoticed.Authors: Dan Wood, Pavan Deolasee, Álvaro HerreraReviewed-by: Masahiko Sawada, Pavan Deolasee, Álvaro HerreraDiscussion:https://postgr.es/m/84EBAC55-F06D-4FBE-A3F3-8BDA093CE3E3@amazon.com
1 parent56a4564 commite1d6347

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-15
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1 file changed

+25
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‎src/backend/access/heap/heapam.c

Lines changed: 25 additions & 15 deletions
Original file line numberDiff line numberDiff line change
@@ -6650,9 +6650,10 @@ heap_prepare_freeze_tuple(HeapTupleHeader tuple,
66506650
xl_heap_freeze_tuple*frz,bool*totally_frozen_p)
66516651
{
66526652
boolchanged= false;
6653-
boolfreeze_xmax= false;
6653+
boolxmax_already_frozen= false;
6654+
boolxmin_frozen;
6655+
boolfreeze_xmax;
66546656
TransactionIdxid;
6655-
booltotally_frozen= true;
66566657

66576658
frz->frzflags=0;
66586659
frz->t_infomask2=tuple->t_infomask2;
@@ -6661,6 +6662,8 @@ heap_prepare_freeze_tuple(HeapTupleHeader tuple,
66616662

66626663
/* Process xmin */
66636664
xid=HeapTupleHeaderGetXmin(tuple);
6665+
xmin_frozen= ((xid==FrozenTransactionId)||
6666+
HeapTupleHeaderXminFrozen(tuple));
66646667
if (TransactionIdIsNormal(xid))
66656668
{
66666669
if (TransactionIdPrecedes(xid,relfrozenxid))
@@ -6679,9 +6682,8 @@ heap_prepare_freeze_tuple(HeapTupleHeader tuple,
66796682

66806683
frz->t_infomask |=HEAP_XMIN_FROZEN;
66816684
changed= true;
6685+
xmin_frozen= true;
66826686
}
6683-
else
6684-
totally_frozen= false;
66856687
}
66866688

66876689
/*
@@ -6704,9 +6706,9 @@ heap_prepare_freeze_tuple(HeapTupleHeader tuple,
67046706
relfrozenxid,relminmxid,
67056707
cutoff_xid,cutoff_multi,&flags);
67066708

6707-
if(flags&FRM_INVALIDATE_XMAX)
6708-
freeze_xmax= true;
6709-
elseif (flags&FRM_RETURN_IS_XID)
6709+
freeze_xmax=(flags&FRM_INVALIDATE_XMAX);
6710+
6711+
if (flags&FRM_RETURN_IS_XID)
67106712
{
67116713
/*
67126714
* NB -- some of these transformations are only valid because we
@@ -6720,7 +6722,6 @@ heap_prepare_freeze_tuple(HeapTupleHeader tuple,
67206722
if (flags&FRM_MARK_COMMITTED)
67216723
frz->t_infomask |=HEAP_XMAX_COMMITTED;
67226724
changed= true;
6723-
totally_frozen= false;
67246725
}
67256726
elseif (flags&FRM_RETURN_IS_MULTI)
67266727
{
@@ -6742,11 +6743,6 @@ heap_prepare_freeze_tuple(HeapTupleHeader tuple,
67426743
frz->xmax=newxmax;
67436744

67446745
changed= true;
6745-
totally_frozen= false;
6746-
}
6747-
else
6748-
{
6749-
Assert(flags&FRM_NOOP);
67506746
}
67516747
}
67526748
elseif (TransactionIdIsNormal(xid))
@@ -6774,11 +6770,24 @@ heap_prepare_freeze_tuple(HeapTupleHeader tuple,
67746770
freeze_xmax= true;
67756771
}
67766772
else
6777-
totally_frozen= false;
6773+
freeze_xmax= false;
67786774
}
6775+
elseif ((tuple->t_infomask&HEAP_XMAX_INVALID)||
6776+
!TransactionIdIsValid(HeapTupleHeaderGetRawXmax(tuple)))
6777+
{
6778+
freeze_xmax= false;
6779+
xmax_already_frozen= true;
6780+
}
6781+
else
6782+
ereport(ERROR,
6783+
(errcode(ERRCODE_DATA_CORRUPTED),
6784+
errmsg_internal("found xmax %u (infomask 0x%04x) not frozen, not multi, not normal",
6785+
xid,tuple->t_infomask)));
67796786

67806787
if (freeze_xmax)
67816788
{
6789+
Assert(!xmax_already_frozen);
6790+
67826791
frz->xmax=InvalidTransactionId;
67836792

67846793
/*
@@ -6831,7 +6840,8 @@ heap_prepare_freeze_tuple(HeapTupleHeader tuple,
68316840
}
68326841
}
68336842

6834-
*totally_frozen_p=totally_frozen;
6843+
*totally_frozen_p= (xmin_frozen&&
6844+
(freeze_xmax||xmax_already_frozen));
68356845
returnchanged;
68366846
}
68376847

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