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Re: Reduction in WAL for UPDATEs

From: Gregory Stark <stark(at)enterprisedb(dot)com>
To: "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: "Kenneth Marshall" <ktm(at)rice(dot)edu>, <pgsql-hackers(at)postgreSQL(dot)org>
Subject: Re: Reduction in WAL for UPDATEs
Date: 2007-03-28 15:05:58
Message-ID: 87y7lhl86h.fsf@oxford.xeocode.com (view raw or flat)
Thread:
Lists: pgsql-hackers
"Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:

> Yeah, this illustrates my concern that the proposal is too narrowly
> focused on a specific benchmark.

A lot of the recently proposed changes don't really fit in the "optimizations"
category very well at all. I think of them more as "avoiding pitfalls".

Currently Postgres works quite well if your application is designed around its
performance profile. But as soon as you do something "strange" you run the
risk of running into various pitfalls.

If you keep a long-running transaction open you suddenly find your tables
bloating. If your table grows too large vacuum takes too long to complete and
your tables bloat. If you update the same record many times instead of
batching updates and performing a single update your table bloats. 

This one is similar, if you keep a bunch of static data attached to some small
dynamic data your WAL and table bloats. Certainly you could have engineered
your system not to fall into this pitfall, but only if you knew about it and
only if it was worth the effort and other possible costs of doing so.

-- 
  Gregory Stark
  EnterpriseDB          http://www.enterprisedb.com


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