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Re: Reduction in WAL for UPDATEs

From: "Joshua D(dot) Drake" <jd(at)commandprompt(dot)com>
To: Gregory Stark <stark(at)enterprisedb(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Kenneth Marshall <ktm(at)rice(dot)edu>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Reduction in WAL for UPDATEs
Date: 2007-03-28 15:14:02
Message-ID: (view raw or whole thread)
Lists: pgsql-hackers
Gregory Stark wrote:
> "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.

I would go a step further. Once you get into real life scenarios with 
real life work loads, you run 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. 

Long-running transaction is a big problem. I wish I knew how to solve it.

> 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.

It seems to me the solution could be useful. We have lots of tables that 
fall into the category that the test table presented.


Joshua D. Drake


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