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Re: Core team statement on replication in PostgreSQL

From: "Merlin Moncure" <mmoncure(at)gmail(dot)com>
To: "Andrew Dunstan" <andrew(at)dunslane(dot)net>
Cc: "Dave Page" <dpage(at)pgadmin(dot)org>, "Douglas McNaught" <doug(at)mcnaught(dot)org>, "Joshua D(dot) Drake" <jd(at)commandprompt(dot)com>, "David Fetter" <david(at)fetter(dot)org>, "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Core team statement on replication in PostgreSQL
Date: 2008-05-29 19:03:40
Message-ID: b42b73150805291203q7e2bc7f5ga551958556be532d@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-advocacypgsql-hackers
On Thu, May 29, 2008 at 12:19 PM, Andrew Dunstan <andrew(at)dunslane(dot)net> wrote:
> That's not what Tom's email said, AIUI. "Synchronous" replication surely
> means that the master and slave always have the same set of transactions
> applied. Streaming <> synchronous. But streaming log shipping will allow us
> to get get closer to synchronicity in some situations, i.e. the window for
> missing transactions will be much smaller.
>
> Some of us were discussing this late on Friday night after PGcon. ISTM that
> we can have either 1) fairly hot failover slaves that are guaranteed to be
> almost up to date, or 2) slaves that can support read-only transactions but
> might get somewhat out of date if they run long transactions. The big
> problem is in having slaves which are both highly up to date and support
> arbitrary read-only transactions. Maybe in the first instance, at least, we
> need to make slaves choose which role they will play.

I personally would be thrilled to have slaves be query-able in any
fashion, even if 'wrong' under certain circumstances.  Any
asynchronous solution by definition gives the wrong answer on the
slave.  Read only slave is the #1 most anticipated feature in the
circles I run with.  It would literally transform how the database
world thinks about postgres overnight.  This, coupled with easier
standby setup (a pg_archive to mirror pg_restore) would be most
welcome!

merlin

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