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Re: PITR performance costs

From: Stephen Frost <sfrost(at)snowman(dot)net>
To: Dave Cramer <pg(at)fastcrypt(dot)com>
Cc: Heikki Linnakangas <heikki(at)enterprisedb(dot)com>,postgresql performance list <pgsql-performance(at)postgresql(dot)org>
Subject: Re: PITR performance costs
Date: 2007-05-28 19:46:03
Message-ID: 20070528194603.GO7531@tamriel.snowman.net (view raw or flat)
Thread:
Lists: pgsql-performance
Dave, et al,

* Dave Cramer (pg(at)fastcrypt(dot)com) wrote:
> Don't the archived logs have to be copied as well as the regular WAL  
> logs get recycled ?

Yes, but I'd expect at the point they're being copied off to some other
store (probably a seperate disk, or even over the network to another
system, etc), they're probably in the system cache, so you're probably
not going out to disk to get those blocks anyway.  That might not be the
case on a slow-write system, but in those cases it seems at least
somewhat unlikely you'll be hit very hard by the occational 16MB copy
off the disk...

	Thanks,

		Stephen

> On 28-May-07, at 12:31 PM, Heikki Linnakangas wrote:
> 
> >Dave Cramer wrote:
> >>Since PITR has to enable archiving does this not increase the  
> >>amount of disk I/O required ?
> >
> >There's no difference in normal DML operations, but some bulk  
> >operations like CREATE INDEX that don't otherwise generate WAL,  
> >need to be WAL logged when archiving is enabled.
> >
> >-- 
> >  Heikki Linnakangas
> >  EnterpriseDB   http://www.enterprisedb.com
> 
> 
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