From: | Alvaro Herrera <alvherre(at)commandprompt(dot)com> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Heikki Linnakangas <heikki(at)enterprisedb(dot)com>, Gokulakannan Somasundaram <gokul007(at)gmail(dot)com>, Markus Schiltknecht <markus(at)bluegap(dot)ch>, Gregory Stark <stark(at)enterprisedb(dot)com>, pgsql-hackers list <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Some ideas about Vacuum |
Date: | 2008-01-16 16:39:43 |
Message-ID: | 20080116163943.GC5076@alvh.no-ip.org |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-hackers |
Tom Lane escribió:
> Alvaro Herrera <alvherre(at)commandprompt(dot)com> writes:
> > Heikki Linnakangas escribi:
> >> Another issue is that reading WAL is inherently not very scalable. There's
> >> only one WAL for the whole cluster, and it needs to be read sequentially,
> >> so it can easily become a bottleneck on large systems.
>
> > I have wondered why do we do it this way. Is there a problem with
> > having one WAL per database, and another for general operations? This
> > last WAL would have changes to shared tables, as well as global stuff
> > like "create database" or "create tablespace".
>
> It would only be useful to have one per spindle-dedicated-to-WAL, so
> tying the division to databases doesn't seem like it'd be a good idea.
Keep in mind that there are claims that a write-cache-enabled
battery-backed RAID controller negates the effect of a separate spindle.
Also, these days people is recommending keeping WAL in a mirrored disk,
so you would have to have a mirrored pair for every WAL stream, which
starts to sound unworkable.
My point, rather, is that with this sort of setup it would be easier to
do per-database PITR shipping, and one database's WAL activity would not
affect another's (thus hosting providers are happier -- high-rate
customer A need not affect low-budget customer B).
A totally separate consideration is that of LWLock contention.
--
Alvaro Herrera http://www.CommandPrompt.com/
PostgreSQL Replication, Consulting, Custom Development, 24x7 support
From | Date | Subject | |
---|---|---|---|
Next Message | Mischa Sandberg | 2008-01-16 16:41:42 | postgresql in FreeBSD jails: proposal |
Previous Message | Tom Lane | 2008-01-16 16:22:57 | Re: Some ideas about Vacuum |