Hi,
On 2013-02-07 16:45:57 +0900, Michael Paquier wrote:
> Please find attached a patch fixing 3 of the 4 problems reported before
> (the patch does not contain docs).
> 1) Removal of the quadratic dependency with list_append_unique_oid
Afaics you now simply lock objects multiple times, is that right?
> 2) Minimization of the wait phase for parent relations, this is done in a
> single transaction before phase 2
Unfortunately I don't think this did the trick. You currently have the
following:
+ /* Perform a wait on each session lock separate transaction */
+ StartTransactionCommand();
+ foreach(lc, lockTags)
+ {
+ LOCKTAG *localTag = (LOCKTAG *) lfirst(lc);
+ Assert(localTag && localTag->locktag_field2 != InvalidOid);
+ WaitForVirtualLocks(*localTag, ShareLock);
+ }
+ CommitTransactionCommand();
and
+void
+WaitForVirtualLocks(LOCKTAG heaplocktag, LOCKMODE lockmode)
+{
+ VirtualTransactionId *old_lockholders;
+
+ old_lockholders = GetLockConflicts(&heaplocktag, lockmode);
+
+ while (VirtualTransactionIdIsValid(*old_lockholders))
+ {
+ VirtualXactLock(*old_lockholders, true);
+ old_lockholders++;
+ }
+}
To get rid of the issue you need to batch all the GetLockConflicts calls
together before doing any of the VirtualXactLocks. Otherwise other
backends will produce new conflicts on relation n+1 while you wait for
relation n.
So it would need to be something like:
void
WaitForVirtualLocksList(List heaplocktags, LOCKMODE lockmode)
{ VirtualTransactionId **old_lockholders; ListCell *lc; int off = 0; int i;
old_lockholders = palloc(sizeof(VirtualTransactionId *) * list_length(heaplocktags));
/* collect transactions we need to wait on for all transactions */foreach(lc, heaplocktags) { LOCKTAG *tag =
lfirst(lc); old_lockholders[off++] = GetLockConflicts(tag, lockmode); }
/* wait on all transactions */ for (i = 0; i < off; i++) { VirtualTransactionId *lockholders =
old_lockholders[i];
while (VirtualTransactionIdIsValid(lockholders[i])) { VirtualXactLock(lockholders[i], true);
lockholders++; } }
}
Makes sense?
Greetings,
Andres Freund
--Andres Freund http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training &
Services
