On Sep 28, 2017 4:30 PM, "Alexander Korotkov" <a.korot...@postgrespro.ru>
wrote:
Hi!
On Wed, Jun 21, 2017 at 10:52 AM, Shubham Barai <shubhambara...@gmail.com>
wrote:
> Hi,
>
> On 21 June 2017 at 13:11, Heikki Linnakangas <hlinn...@iki.fi> wrote:
>
>> On 06/16/2017 01:24 PM, Shubham Barai wrote:
>>
>>> @@ -497,6 +499,13 @@ gistplacetopage(Relation rel, Size freespace,
>>> GISTSTATE *giststate,
>>> for (ptr = dist->next; ptr; ptr = ptr->next)
>>> UnlockReleaseBuffer(ptr->buffer);
>>> }
>>> +
>>> + for (ptr = dist; ptr; ptr = ptr->next)
>>> + PredicateLockPageSplit(rel,
>>> +
>>> BufferGetBlockNumber(buffer),
>>> +
>>> BufferGetBlockNumber(ptr->buffer));
>>> +
>>> +
>>>
>>
>> I think this new code needs to go before the UnlockReleaseBuffer() calls
>> above. Calling BufferGetBlockNumber() on an already-released buffer is not
>> cool.
>>
>> - Heikki
>>
>> I know that. This is the old version of the patch. I had sent updated
> patch later. Please have a look at updated patch.
>
I took a look on this patch.
In gistdoinsert() you do CheckForSerializableConflictIn() only if page
wasn't exclusively locked before (xlocked is false).
if (!xlocked)
> {
> LockBuffer(stack->buffer, GIST_UNLOCK);
> LockBuffer(stack->buffer, GIST_EXCLUSIVE);
> CheckForSerializableConflictIn(r, NULL, stack->buffer);
> xlocked = true;
However, page might be exclusively locked before. And in this case
CheckForSerializableConflictIn() would be skipped. That happens very
rarely (someone fixes incomplete split before we did), but nevertheless.
I agree with Andrey Borodin's view on locks. I am quoting his message
"if xlocked = true, page was already checked for conflict after setting
exclusive lock on it's buffer. I still do not see any problem here..."
Regards,
Shubham
