Re: heap_update temporary release of buffer lock

Alvaro Herrera <alvherre(at)commandprompt(dot)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)?

regards, tom lane