| From: | Michael Paquier <michael(dot)paquier(at)gmail(dot)com> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | Fujii Masao <masao(dot)fujii(at)gmail(dot)com>, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>, Petr Jelinek <petr(at)2ndquadrant(dot)com>, Vik Fearing <vik(at)2ndquadrant(dot)fr>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Josh Berkus <josh(at)agliodbs(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Quorum commit for multiple synchronous replication. |
| Date: | 2016-12-08 07:39:45 |
| Message-ID: | CAB7nPqTwDHDDNv6rkCPUg4p03=e4kzU0BN_5KLnnAR8FkmndMw@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Thu, Dec 8, 2016 at 9:07 AM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> You could do that, but first I would code up the simplest, cleanest
> algorithm you can think of and see if it even shows up in a 'perf'
> profile. Microbenchmarking is probably overkill here unless a problem
> is visible on macrobenchmarks.
This is what I would go for! The current code is doing a simple thing:
select the Nth element using qsort() after scanning each WAL sender's
values. And I think that Sawada-san got it right. Even running on my
laptop a pgbench run with 10 sync standbys using a data set that fits
into memory, SyncRepGetOldestSyncRecPtr gets at most 0.04% of overhead
using perf top on a non-assert, non-debug build. Hash tables and
allocations get a far larger share. Using the patch,
SyncRepGetSyncRecPtr is at the same level with a quorum set of 10
nodes. Let's kick the ball for now. An extra patch could make things
better later on if that's worth it.
--
Michael
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