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Commit2bf372a

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heap_prepare_freeze_tuple: Simplify coding
Commitd2599ec introduced some contorted, confused code around:readers would think that it's possible for HeapTupleHeaderGetXmin returna non-frozen value for some frozen tuples, which would be disastrous.There's no actual bug, but it seems better to make it clearer.Per gripe from Tom Lane and Andres Freund.Discussion:https://postgr.es/m/30116.1555430496@sss.pgh.pa.us
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‎src/backend/access/heap/heapam.c

Lines changed: 13 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -6106,19 +6106,27 @@ heap_prepare_freeze_tuple(HeapTupleHeader tuple,
61066106
frz->t_infomask=tuple->t_infomask;
61076107
frz->xmax=HeapTupleHeaderGetRawXmax(tuple);
61086108

6109-
/* Process xmin */
6109+
/*
6110+
* Process xmin. xmin_frozen has two slightly different meanings: in the
6111+
* !XidIsNormal case, it means "the xmin doesn't need any freezing" (it's
6112+
* already a permanent value), while in the block below it is set true to
6113+
* mean "xmin won't need freezing after what we do to it here" (false
6114+
* otherwise). In both cases we're allowed to set totally_frozen, as far
6115+
* as xmin is concerned.
6116+
*/
61106117
xid=HeapTupleHeaderGetXmin(tuple);
6111-
xmin_frozen= ((xid==FrozenTransactionId)||
6112-
HeapTupleHeaderXminFrozen(tuple));
6113-
if (TransactionIdIsNormal(xid))
6118+
if (!TransactionIdIsNormal(xid))
6119+
xmin_frozen= true;
6120+
else
61146121
{
61156122
if (TransactionIdPrecedes(xid,relfrozenxid))
61166123
ereport(ERROR,
61176124
(errcode(ERRCODE_DATA_CORRUPTED),
61186125
errmsg_internal("found xmin %u from before relfrozenxid %u",
61196126
xid,relfrozenxid)));
61206127

6121-
if (TransactionIdPrecedes(xid,cutoff_xid))
6128+
xmin_frozen=TransactionIdPrecedes(xid,cutoff_xid);
6129+
if (xmin_frozen)
61226130
{
61236131
if (!TransactionIdDidCommit(xid))
61246132
ereport(ERROR,
@@ -6128,7 +6136,6 @@ heap_prepare_freeze_tuple(HeapTupleHeader tuple,
61286136

61296137
frz->t_infomask |=HEAP_XMIN_FROZEN;
61306138
changed= true;
6131-
xmin_frozen= true;
61326139
}
61336140
}
61346141

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