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Re: Quorum commit for multiple synchronous replication.

Michael Paquier <michael.paquier@gmail.com>

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From: Michael Paquier <michael.paquier@gmail.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Fujii Masao <masao.fujii@gmail.com>, Masahiko Sawada <sawada.mshk@gmail.com>, Petr Jelinek <petr@2ndquadrant.com>, Vik Fearing <vik@2ndquadrant.fr>, Simon Riggs <simon@2ndquadrant.com>, Josh Berkus <josh@agliodbs.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2016-12-08T07:39:45Z
Lists: pgsql-hackers 
On Thu, Dec 8, 2016 at 9:07 AM, Robert Haas <robertmhaas@gmail.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

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Set the priorities of all quorum synchronous standbys to 1.

  2. Improve documentation and comment for quorum-based sync replication.