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Commitd2599ec

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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 parent966268c commitd2599ec

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1 file changed

+25
-15
lines changed

1 file changed

+25
-15
lines changed

‎src/backend/access/heap/heapam.c

Lines changed: 25 additions & 15 deletions
Original file line numberDiff line numberDiff line change
@@ -6803,9 +6803,10 @@ heap_prepare_freeze_tuple(HeapTupleHeader tuple,
68036803
xl_heap_freeze_tuple*frz,bool*totally_frozen_p)
68046804
{
68056805
boolchanged= false;
6806-
boolfreeze_xmax= false;
6806+
boolxmax_already_frozen= false;
6807+
boolxmin_frozen;
6808+
boolfreeze_xmax;
68076809
TransactionIdxid;
6808-
booltotally_frozen= true;
68096810

68106811
frz->frzflags=0;
68116812
frz->t_infomask2=tuple->t_infomask2;
@@ -6814,6 +6815,8 @@ heap_prepare_freeze_tuple(HeapTupleHeader tuple,
68146815

68156816
/* Process xmin */
68166817
xid=HeapTupleHeaderGetXmin(tuple);
6818+
xmin_frozen= ((xid==FrozenTransactionId)||
6819+
HeapTupleHeaderXminFrozen(tuple));
68176820
if (TransactionIdIsNormal(xid))
68186821
{
68196822
if (TransactionIdPrecedes(xid,relfrozenxid))
@@ -6832,9 +6835,8 @@ heap_prepare_freeze_tuple(HeapTupleHeader tuple,
68326835

68336836
frz->t_infomask |=HEAP_XMIN_FROZEN;
68346837
changed= true;
6838+
xmin_frozen= true;
68356839
}
6836-
else
6837-
totally_frozen= false;
68386840
}
68396841

68406842
/*
@@ -6857,9 +6859,9 @@ heap_prepare_freeze_tuple(HeapTupleHeader tuple,
68576859
relfrozenxid,relminmxid,
68586860
cutoff_xid,cutoff_multi,&flags);
68596861

6860-
if(flags&FRM_INVALIDATE_XMAX)
6861-
freeze_xmax= true;
6862-
elseif (flags&FRM_RETURN_IS_XID)
6862+
freeze_xmax=(flags&FRM_INVALIDATE_XMAX);
6863+
6864+
if (flags&FRM_RETURN_IS_XID)
68636865
{
68646866
/*
68656867
* NB -- some of these transformations are only valid because we
@@ -6873,7 +6875,6 @@ heap_prepare_freeze_tuple(HeapTupleHeader tuple,
68736875
if (flags&FRM_MARK_COMMITTED)
68746876
frz->t_infomask |=HEAP_XMAX_COMMITTED;
68756877
changed= true;
6876-
totally_frozen= false;
68776878
}
68786879
elseif (flags&FRM_RETURN_IS_MULTI)
68796880
{
@@ -6895,11 +6896,6 @@ heap_prepare_freeze_tuple(HeapTupleHeader tuple,
68956896
frz->xmax=newxmax;
68966897

68976898
changed= true;
6898-
totally_frozen= false;
6899-
}
6900-
else
6901-
{
6902-
Assert(flags&FRM_NOOP);
69036899
}
69046900
}
69056901
elseif (TransactionIdIsNormal(xid))
@@ -6927,11 +6923,24 @@ heap_prepare_freeze_tuple(HeapTupleHeader tuple,
69276923
freeze_xmax= true;
69286924
}
69296925
else
6930-
totally_frozen= false;
6926+
freeze_xmax= false;
69316927
}
6928+
elseif ((tuple->t_infomask&HEAP_XMAX_INVALID)||
6929+
!TransactionIdIsValid(HeapTupleHeaderGetRawXmax(tuple)))
6930+
{
6931+
freeze_xmax= false;
6932+
xmax_already_frozen= true;
6933+
}
6934+
else
6935+
ereport(ERROR,
6936+
(errcode(ERRCODE_DATA_CORRUPTED),
6937+
errmsg_internal("found xmax %u (infomask 0x%04x) not frozen, not multi, not normal",
6938+
xid,tuple->t_infomask)));
69326939

69336940
if (freeze_xmax)
69346941
{
6942+
Assert(!xmax_already_frozen);
6943+
69356944
frz->xmax=InvalidTransactionId;
69366945

69376946
/*
@@ -6984,7 +6993,8 @@ heap_prepare_freeze_tuple(HeapTupleHeader tuple,
69846993
}
69856994
}
69866995

6987-
*totally_frozen_p=totally_frozen;
6996+
*totally_frozen_p= (xmin_frozen&&
6997+
(freeze_xmax||xmax_already_frozen));
69886998
returnchanged;
69896999
}
69907000

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