Re: AdvanceXLInsertBuffer vs. WAL segment compressibility

On Thu, Jul 6, 2017 at 3:48 PM, Heikki Linnakangas <hlinnaka(at)iki(dot)fi> wrote:
> On 07/03/2017 06:30 PM, Chapman Flack wrote:
>> Although it's moot in the straightforward approach of re-zeroing in
>> the loop, it would still help my understanding of the system to know
>> if there is some subtlety that would have broken what I proposed
>> earlier, which was an extra flag to AdvanceXLInsertBuffer() that
>> would tell it not only to skip initializing headers, but also to
>> skip the WaitXLogInsertionsToFinish() check ... because I have
>> the entire region reserved and I hold all the writer slots
>> at that moment, it seems safe to assure AdvanceXLInsertBuffer()
>> that there are no outstanding writes to wait for.
>
> Yeah, I suppose that would work, too.

FWIW, I would rather see any optimization done in
AdvanceXLInsertBuffer() instead of seeing a second memset re-zeroing
the WAL page header after its data has been initialized by
AdvanceXLInsertBuffer() once. That's too late for 10, but you still
have time for a patch to be integrated in 11.
--
Michael