mirror/postgresql
2
0
Fork 0
mirror of https://git.postgresql.org/git/postgresql.git synced 2024-12-21 08:29:39 +08:00
Code Issues Packages Projects Releases Wiki Activity

Compare Xmin to previous Xmax when locking an update chain

Browse Source 
Not doing so causes us to traverse an update chain that has been broken
by concurrent page pruning.  All other code that traverses update chains
uses this check as one of the cases in which to stop iterating, so
replicate it here too.  Failure to do so leads to erroneous CLOG,
subtrans or multixact lookups.

Per discussion following the bug report by J Smith in
CADFUPgc5bmtv-yg9znxV-vcfkb+JPRqs7m2OesQXaM_4Z1JpdQ@mail.gmail.com
as diagnosed by Andres Freund.
This commit is contained in:
Alvaro Herrera 2013-11-27 17:49:12 -03:00
parent c235a6a589
commit e4828e9ccb
1 changed files with 14 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

14
src/backend/access/heap/heapam.c
View File

@ -4814,6 +4814,7 @@ heap_lock_updated_tuple_rec(Relation rel, ItemPointer tid, TransactionId xid,
old_infomask; old_infomask;
TransactionId xmax, TransactionId xmax,
new_xmax; new_xmax;
TransactionId priorXmax = InvalidTransactionId;
ItemPointerCopy(tid, &tupid); ItemPointerCopy(tid, &tupid);
@ -4839,6 +4840,18 @@ l4:
CHECK_FOR_INTERRUPTS(); CHECK_FOR_INTERRUPTS();
LockBuffer(buf, BUFFER_LOCK_EXCLUSIVE); LockBuffer(buf, BUFFER_LOCK_EXCLUSIVE);
/*
* Check the tuple XMIN against prior XMAX, if any. If we reached
* the end of the chain, we're done, so return success.
*/
if (TransactionIdIsValid(priorXmax) &&
!TransactionIdEquals(HeapTupleHeaderGetXmin(mytup.t_data),
priorXmax))
{
UnlockReleaseBuffer(buf);
return HeapTupleMayBeUpdated;
}
old_infomask = mytup.t_data->t_infomask; old_infomask = mytup.t_data->t_infomask;
xmax = HeapTupleHeaderGetRawXmax(mytup.t_data); xmax = HeapTupleHeaderGetRawXmax(mytup.t_data);
@ -4939,6 +4952,7 @@ l4:
} }
/* tail recursion */ /* tail recursion */
priorXmax = HeapTupleHeaderGetUpdateXid(mytup.t_data);
ItemPointerCopy(&(mytup.t_data->t_ctid), &tupid); ItemPointerCopy(&(mytup.t_data->t_ctid), &tupid);
UnlockReleaseBuffer(buf); UnlockReleaseBuffer(buf);
} }