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04-19-2008, 08:48 AM
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 Re: Defining performance. [nospam@hardgeus.com - Thu at 06:37:12PM -0600] > As my dataset has gotten larger I have had to throw more metal at the > problem, but I have also had to rethink my table and query design. Just > because your data set grows linearly does NOT mean that the performance of > your query is guaranteed to grow linearly! A sloppy query that runs OK > with 3000 rows in your table may choke horribly when you hit 50000. Then some limit is hit ... either the memory cache, or that the planner is doing an unlucky change of strategy when hitting 50000. Anyway, it's very important when testing queries that they actually are tested on a (copy of the) production database, and not on an empty database or a database containing some random test data. If testing queries off the production database, it's important to have equal hardware and configuration on both servers. ---------------------------(end of broadcast)--------------------------- TIP 7: You can help support the PostgreSQL project by donating at http://www.postgresql.org/about/donate      |
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04-19-2008, 08:48 AM
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| Re: Defining performance. Tobias Brox wrote: > [nospam@hardgeus.com - Thu at 06:37:12PM -0600] >> As my dataset has gotten larger I have had to throw more metal at the >> problem, but I have also had to rethink my table and query design. Just >> because your data set grows linearly does NOT mean that the performance of >> your query is guaranteed to grow linearly! A sloppy query that runs OK >> with 3000 rows in your table may choke horribly when you hit 50000. > > Then some limit is hit ... either the memory cache, or that the planner > is doing an unlucky change of strategy when hitting 50000. Not really. A bad query is a bad query (eg missing a join element). It won't show up for 3000 rows, but will very quickly if you increase that by a reasonable amount. Even as simple as a missing index on a join column won't show up for a small dataset but will for a larger one. It's a pretty common mistake to assume that a small dataset will behave exactly the same as a larger one - not always the case. -- Postgresql & php tutorials http://www.designmagick.com/ ---------------------------(end of broadcast)--------------------------- TIP 7: You can help support the PostgreSQL project by donating at http://www.postgresql.org/about/donate |
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