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Re: ??: Postgresql update op is very very slow

From: Greg Smith <gsmith(at)gregsmith(dot)com>
To: Holger Hoffstaette <holger(at)wizards(dot)de>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: ??: Postgresql update op is very very slow
Date: 2008-06-26 22:15:14
Message-ID: Pine.GSO.4.64.0806261758340.22988@westnet.com (view raw or flat)
Thread:
Lists: pgsql-performance
On Thu, 26 Jun 2008, Holger Hoffstaette wrote:

> How do large databases treat mass updates? AFAIK both DB2 and Oracle use 
> MVCC (maybe a different kind?) as well

An intro to the other approaches used by Oracle and DB2 (not MVCC) is at

http://wiki.postgresql.org/wiki/Why_PostgreSQL_Instead_of_MySQL:_Comparing_Reliability_and_Speed_in_2007#Transaction_Locking_and_Scalability

(a URL which I really need to shorten one day).

> Are there no options (algorithms) for adaptively choosing different 
> update strategies that do not incur the full MVCC overhead?

If you stare at the big picture of PostgreSQL's design, you might notice 
that it usually aims to do things one way and get that implementation 
right for the database's intended audience.  That intended audience cares 
about data integrity and correctness and is willing to suffer the overhead 
that goes along with operating that way.  There's few "I don't care about 
reliability here so long as it's fast" switches you can flip, and not 
having duplicate code paths to support them helps keep the code simpler 
and therefore more reliable.

This whole area is one of those good/fast/cheap trios.  If you want good 
transaction guarantees on updates, you either get the hardware and 
settings right to handle that (!cheap), or it's slow.  The idea of 
providing a !good/fast/cheap option for updates might have some 
theoretical value, but I think you'd find it hard to get enough support 
for that idea to get work done on it compared to the other things 
developer time is being spent on right now.

--
* Greg Smith gsmith(at)gregsmith(dot)com http://www.gregsmith.com Baltimore, MD

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