| From: | Bruce Momjian <bruce(at)momjian(dot)us> |
|---|---|
| To: | Alfred Perlstein <alfred(at)freebsd(dot)org> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Stephen Frost <sfrost(at)snowman(dot)net>, Robert Haas <robertmhaas(at)gmail(dot)com>, Geoff Winkless <pgsqladmin(at)geoff(dot)dj>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Why we lost Uber as a user |
| Date: | 2016-08-03 13:33:07 |
| Message-ID: | 20160803133307.GA13027@momjian.us |
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| Lists: | pgsql-hackers |
On Tue, Aug 2, 2016 at 10:33:15PM -0400, Bruce Momjian wrote:
> I saw from the Uber article that they weren't going to per-row logical
> replication but _statement_ replication, which is very hard to do
> because typical SQL doesn't record what concurrent transactions
> committed before a new statement's transaction snapshot is taken, and
> doesn't record lock order for row updates blocked by concurrent activity
> --- both of which affect the final result from the query.
>
> So, for statement replication, it is not a question of whether the code
> has bugs, but that the replay is not 100% possible in all cases, unless
> you switch to some statement-row-lock hybrid ability.
Oh, and one more problem with statement-level replication is that the
overhead of statement replay is high, as high as it was on the master.
That leaves minimal server resources left to handle read-only workloads
on the slave.
--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com
+ As you are, so once was I. As I am, so you will be. +
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