Re: heap_update temporary release of buffer lock

On Tue, Sep 20, 2011 at 3:47 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Alvaro Herrera <alvherre@commandprompt.com> writes:
>> Excerpts from Robert Haas's message of mar sep 20 16:04:03 -0300 2011:
>>>> On 20.09.2011 20:42, Alvaro Herrera wrote:
>>>>> I notice that heap_update releases the buffer lock, after checking the
>>>>> HeapTupleSatifiesUpdate result, and before marking the tuple as updated,
>>>>> to pin the visibility map page -- heapam.c lines 2638ff in master branch.
>
>>> The easiest fix seems to be (as you suggest) to add "goto l2" after
>>> reacquiring the lock.  Can we get away with (and is there any benefit
>>> to) doing that only if xmax has changed?
>
>> Hmm ... I think that works, and it would suit my purposes too.  Note
>> this means you have to recheck infomask too (otherwise consider that
>> IS_MULTI could be set the first time, and not set the second time, and
>> that makes the Xmax have a different meaning.)  OTOH if you just do it
>> always, it is simpler.
>
> Yeah, I think a "goto l2" is correct and sufficient.  As the comment
> already notes, this need not be a high-performance path, so why spend
> extra code (with extra risk of bugs)?

Done.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company