Re: Reduce amount of WAL generated by CREATE INDEX for gist, gin and sp-gist

On 30.11.2018 15:10, Dmitry Dolgov wrote:
> Thank you. I played a bit with this patch, and can confirm visible WAL size
> reduction (it's rather obvious, but still). Although, probably due to lack of
> my knowledge here, I wonder how does it work when an index is build
> concurrently?

Routine generate_xlog_for_rel() works only at phase 2 of concurrent
index building.
At the phase 3, during validate_index() execution we use aminsert() ->
PlaceToPage() mechanism as before the patch.
In the concurrent mode, I do not expect any problems, caused by the patch.

>
>> Benchmarks:
>> -----------
>>
>> Test: pgbench -f gin-WAL-test.sql -t 5:
>> ---------------------------------------
>> master:
>> Latency average: 27696.299 ms
>> WAL size: 2.66 GB
>
> Does it makes sense to measure latency of the entire script, since it contains
> also some preparation work? Of course it still shows the difference between
> patched version and master, but probably in a more noisy way.

Ok. It is used only for demonstration.

--
Andrey Lepikhov
Postgres Professional
https://postgrespro.com
The Russian Postgres Company