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Re: speeding up table creation

From: Steve Crawford <scrawford(at)pinpointresearch(dot)com>
To: Rainer Mager <rainer(at)vanten(dot)com>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: speeding up table creation
Date: 2008-10-14 23:56:41
Message-ID: 48F531B9.9010302@pinpointresearch.com (view raw or flat)
Thread:
Lists: pgsql-performance
Rainer Mager wrote:
>
> I have an interesting performance improvement need. As part of the 
> automatic test suite we run in our development environment, we 
> re-initialize our test database a number of times in order to ensure 
> it is clean before running a test. We currently do this by dropping 
> the public schema and then recreating our tables (roughly 30 tables 
> total). After that we do normal inserts, etc, but never with very much 
> data. My question is, what settings can we tweak to improve 
> performance is this scenario? Specifically, if there was a way to tell 
> Postgres to keep all operations in memory, that would probably be ideal.
>

What is the test part? In other words, do you start with a known initial 
database with all empty tables then run the tests or is part of the test 
itself the creation of those tables? How much data is in the initial 
database if the tables aren't empty. Creating 30 empty tables should 
take a trivial amount of time. Also, are there other schemas than public?

A couple ideas/comments:

You cannot keep the data in memory (that is, you can't disable writing 
to the disk). But since you don't care about data loss, you could turn 
off fsync in postgresql.conf. From a test perspective you should be fine 
- it will only be an issue in the event of a crash and then you can just 
restart with a fresh load. Remember, however, that any performance 
benchmarks won't translate to production use (of course they don't 
translate if you are using ramdisk anyway).

Note that the system tables are updated whenever you add/delete/modify 
tables. Make sure they are being vacuumed or your performance will 
slowly degrade.

My approach is to create a database exactly as you want it to be at the 
start of your tests (fully vacuumed and all) and then use it as a 
template to be used to create the testdb each time. Then you can just 
(with appropriate connection options) run "dropdb thetestdb" followed by 
"createdb --template thetestdbtemplate thetestdb" which is substantially 
faster than deleting and recreating tables - especially if they contain 
much data.

Cheers,
Steve


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