Re: Horizontal scalability/sharding

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: Petr Jelinek <petr(at)2ndquadrant(dot)com>
Cc: Josh Berkus <josh(at)agliodbs(dot)com>, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Horizontal scalability/sharding
Date: 2015-09-03 10:57:09
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On Thu, Sep 3, 2015 at 10:33:12AM +0200, Petr Jelinek wrote:
> On 2015-09-02 19:57, Josh Berkus wrote:
> > On 09/01/2015 04:14 PM, Petr Jelinek wrote:
> >> On 2015-09-02 00:09, Josh Berkus wrote:
> >>> Not really, the mechanism is different and the behavior is different.
> >>> One critical deficiency in using binary syncrep is that you can't do
> >>> round-robin redundancy at all; every redundant node has to be an exact
> >>> mirror of another node. In a good HA distributed system, you want
> >>> multiple shards per node, and you want each shard to be replicated to a
> >>> different node, so that in the event of node failure you're not dumping
> >>> the full load on one other server.
> >>>
> >>
> >> This assumes that we use binary replication, but we can reasonably use
> >> logical replication which can quite easily do filtering of what's
> >> replicated where.
> >
> > Is there a way to do logical synchronous replication? I didn't think
> > there was.
> >
> Yes, the logical replication has similar syncrep properties as the
> binary one (feedback works same way).

Yes, I assumed that. Logical replication uses WAL, so if you are
synchronous with WAL, logical replication is synchronous too. However,
of course, it is synchronous in being durable, not synchronous in terms
of applying the WAL. This is true of binary and logical replication.

Bruce Momjian <bruce(at)momjian(dot)us>

+ Everyone has their own god. +

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