Re: On conflict update & hint bits

On 24.10.2016 00:49, Peter Geoghegan wrote:
> On Sun, Oct 23, 2016 at 2:46 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> What's bothering me is (a) it's less than 24 hours to release wrap and
>> (b) this patch changes SSI-relevant behavior and hasn't been approved
>> by Kevin.  I'm not familiar enough with that logic to commit a change
>> in it on my own authority, especially with so little time for problems
>> to be uncovered.
> I should point out that I knew that the next set of point releases had
> been moved forward much later than you did. I had to work on this fix
> during the week, which was pretty far from ideal for me for my own
> reasons.
>
Just for information: I know that you are working on this issue, but as 
far as we need to proceed further with our testing of multimaster,
I have done the following obvious changes and it fixes the problem (at 
least this assertion failure is not happen any more):

src/backend/executor/nodeModifyTable.c

@@ -1087,6 +1087,13 @@ ExecOnConflictUpdate(ModifyTableState *mtstate,     test = heap_lock_tuple(relation, &tuple,
estate->es_output_cid,                           lockmode, LockWaitBlock, false, &buffer,
&hufd);
+    /*
+     * We must hold share lock on the buffer content while examining tuple
+     * visibility.  Afterwards, however, the tuples we have found to be
+     * visible are guaranteed good as long as we hold the buffer pin.
+     */
+    LockBuffer(buffer, BUFFER_LOCK_SHARE);
+     switch (test)     {         case HeapTupleMayBeUpdated:
@@ -1142,6 +1149,7 @@ ExecOnConflictUpdate(ModifyTableState *mtstate,              * loop here, as the new version of
therow might not conflict              * anymore, or the conflicting tuple has actually been 
 
deleted.              */
+            LockBuffer(buffer, BUFFER_LOCK_UNLOCK);             ReleaseBuffer(buffer);             return false;

@@ -1175,6 +1183,8 @@ ExecOnConflictUpdate(ModifyTableState *mtstate,     /* Store target's existing tuple in the
state'sdedicated slot */     ExecStoreTuple(&tuple, mtstate->mt_existing, buffer, false);
 

+    LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
+     /*      * Make tuple and any needed join variables available to ExecQual and      * ExecProject.  The EXCLUDED
tupleis installed in 
 
ecxt_innertuple, while

-- 
Konstantin Knizhnik
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