Re: Issues with Quorum Commit

On Wed, 2010-10-06 at 10:57 -0700, Josh Berkus wrote:

> I also strongly believe that we should get single-standby
> functionality committed and tested *first*, before working further on
> multi-standby.

Yes, lets get k = 1 first.

With k = 1 the number of standbys is not limited, so we can still have
very robust and highly available architectures. So we mean
"first-acknowledgement-releases-waiters".

> (1) Consistency: this is another DBA-false-confidence issue.  DBAs who
> implement (1) are liable to do so thinking that they are not only
> guaranteeing the consistency of every standby with the master, but the
> consistency of every standby with every other standby -- a kind of
> dummy multi-master.  They are not, so it will take multiple reminders
> and workarounds in the docs to explain this.  And we'll get complaints
> anyway.

This puts the matter very clearly. Setting k = N is not as good an idea
as it sounds when first described.

-- Simon Riggs           www.2ndQuadrant.comPostgreSQL Development, 24x7 Support, Training and Services