Monday, November 24, 2014

speeding up tests with Postgres

Dear Lazyweb,

I'm developing a site using Django and Postgres. How can I get my tests to run a lot faster?

Answer: tell Postgres to use a tablespace in RAM. Selects, updates, and inserts will run at fast RAM speed vs slow disk speed.

Caveat: this doesn't work for writes. Postgres is designed to keep data reliable at all times. Any INSERT/UPDATE/DELETE gets written to a "write-ahead log" (WAL), so that if the database crashed it'll restore the data.  Since this is on a disk no matter what the tablespace, the above trick doesn't work without defeating the WAL.

Answer2: use UNLOGGED tables, TBD.


Unlogged table performance in postgresql 9.1: (2011) "unlogged tables have shown an increase of output by 13~17%"; includes performance-oriented Postgres settings.

WAITING FOR 9.1 – UNLOGGED TABLES (2011): "that's really fast"

wal_buffers performance by Robert Haas (2012): pretty graphs

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