| From: | Simon Riggs <simon(at)2ndQuadrant(dot)com> |
|---|---|
| To: | Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> |
| Cc: | Fujii Masao <masao(dot)fujii(at)gmail(dot)com>, pavan(dot)deolasee(at)gmail(dot)com, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Synchronous replication patch v2 |
| Date: | 2008-11-14 18:29:46 |
| Message-ID: | 1226687386.27904.645.camel@ebony.2ndQuadrant |
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| Thread: | |
| Lists: | pgsql-hackers |
On Fri, 2008-11-14 at 19:23 +0200, Heikki Linnakangas wrote:
> Simon Riggs wrote:
> > On Fri, 2008-11-14 at 19:00 +0200, Heikki Linnakangas wrote:
> >> Why do we need a separate XLogsndRqst variable in shared memory? Don't
> >> we always want to send the WAL up to the same point as we flush it?
> >
> > If we're doing synch rep and we're committing.
>
> You flush and send the WAL, up to the same point?
Yes, but you may make progress towards it in different size steps.
> > What happens when we're
> > doing async rep or running something like a large load.
>
> You don't flush, and you don't request the WAL to be sent? The
> background writer and WAL sender can still wake up periodically, and
> write and send the WAL as they find convenient.
With WAL writes we write and flush at the same time. With WAL sending
that doesn't sound such a good plan.
--
Simon Riggs www.2ndQuadrant.com
PostgreSQL Training, Services and Support
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