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Commitb78647a

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Restrict infomask bits to set on multixacts
We must only set the bit(s) for the strongest lock held in the tuple;otherwise, a multixact containing members with exclusive lock andkey-share lock will behave as though only a share lock is held.This bug was introduced in commit0ac5ad5, somewhere alongdevelopment, when we allowed a singleton FOR SHARE lock to beimplemented without a MultiXact by using a multi-bit pattern.I overlooked that GetMultiXactIdHintBits() needed to be tweaked as well.Previously, we could have the bits for FOR KEY SHARE and FOR UPDATEsimultaneously set and it wouldn't cause a problem.Per report from digoal@126.com
1 parent77a3082 commitb78647a

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+37
-9
lines changed

1 file changed

+37
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‎src/backend/access/heap/heapam.c‎

Lines changed: 37 additions & 9 deletions
Original file line numberDiff line numberDiff line change
@@ -3269,7 +3269,13 @@ heap_update(Relation relation, ItemPointer otid, HeapTuple newtup,
32693269
&xmax_old_tuple,&infomask_old_tuple,
32703270
&infomask2_old_tuple);
32713271

3272-
/* And also prepare an Xmax value for the new copy of the tuple */
3272+
/*
3273+
* And also prepare an Xmax value for the new copy of the tuple. If there
3274+
* was no xmax previously, or there was one but all lockers are now gone,
3275+
* then use InvalidXid; otherwise, get the xmax from the old tuple. (In
3276+
* rare cases that might also be InvalidXid and yet not have the
3277+
* HEAP_XMAX_INVALID bit set; that's fine.)
3278+
*/
32733279
if ((oldtup.t_data->t_infomask&HEAP_XMAX_INVALID)||
32743280
(checked_lockers&& !locker_remains))
32753281
xmax_new_tuple=InvalidTransactionId;
@@ -3283,6 +3289,12 @@ heap_update(Relation relation, ItemPointer otid, HeapTuple newtup,
32833289
}
32843290
else
32853291
{
3292+
/*
3293+
* If we found a valid Xmax for the new tuple, then the infomask bits
3294+
* to use on the new tuple depend on what was there on the old one.
3295+
* Note that since we're doing an update, the only possibility is that
3296+
* the lockers had FOR KEY SHARE lock.
3297+
*/
32863298
if (oldtup.t_data->t_infomask&HEAP_XMAX_IS_MULTI)
32873299
{
32883300
GetMultiXactIdHintBits(xmax_new_tuple,&infomask_new_tuple,
@@ -5161,6 +5173,7 @@ GetMultiXactIdHintBits(MultiXactId multi, uint16 *new_infomask,
51615173
uint16bits=HEAP_XMAX_IS_MULTI;
51625174
uint16bits2=0;
51635175
boolhas_update= false;
5176+
LockTupleModestrongest=LockTupleKeyShare;
51645177

51655178
/*
51665179
* We only use this in multis we just created, so they cannot be values
@@ -5170,32 +5183,47 @@ GetMultiXactIdHintBits(MultiXactId multi, uint16 *new_infomask,
51705183

51715184
for (i=0;i<nmembers;i++)
51725185
{
5186+
LockTupleModemode;
5187+
5188+
/*
5189+
* Remember the strongest lock mode held by any member of the
5190+
* multixact.
5191+
*/
5192+
mode=TUPLOCK_from_mxstatus(members[i].status);
5193+
if (mode>strongest)
5194+
strongest=mode;
5195+
5196+
/* See what other bits we need */
51735197
switch (members[i].status)
51745198
{
51755199
caseMultiXactStatusForKeyShare:
5176-
bits |=HEAP_XMAX_KEYSHR_LOCK;
5177-
break;
51785200
caseMultiXactStatusForShare:
5179-
bits |=HEAP_XMAX_SHR_LOCK;
5180-
break;
51815201
caseMultiXactStatusForNoKeyUpdate:
5182-
bits |=HEAP_XMAX_EXCL_LOCK;
51835202
break;
5203+
51845204
caseMultiXactStatusForUpdate:
5185-
bits |=HEAP_XMAX_EXCL_LOCK;
51865205
bits2 |=HEAP_KEYS_UPDATED;
51875206
break;
5207+
51885208
caseMultiXactStatusNoKeyUpdate:
5189-
bits |=HEAP_XMAX_EXCL_LOCK;
51905209
has_update= true;
51915210
break;
5211+
51925212
caseMultiXactStatusUpdate:
5193-
bits |=HEAP_XMAX_EXCL_LOCK;
51945213
bits2 |=HEAP_KEYS_UPDATED;
51955214
has_update= true;
51965215
break;
51975216
}
51985217
}
5218+
5219+
if (strongest==LockTupleExclusive||
5220+
strongest==LockTupleNoKeyExclusive)
5221+
bits |=HEAP_XMAX_EXCL_LOCK;
5222+
elseif (strongest==LockTupleShare)
5223+
bits |=HEAP_XMAX_SHR_LOCK;
5224+
elseif (strongest==LockTupleKeyShare)
5225+
bits |=HEAP_XMAX_KEYSHR_LOCK;
5226+
51995227
if (!has_update)
52005228
bits |=HEAP_XMAX_LOCK_ONLY;
52015229

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