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Displaying posts with tag: mysql performance iostat (reset)

mysql I/O performance analysis with iostat
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Here is a situation I’ve run into a few times when dealing with mysql databases. We’re trying to run a one-off query against a high-traffic, large table and the WHERE condition is against a non-indexed field. Let’s say our table is 5GB in size. We issue the following:

SELECT count(*) from five_gb_myisam_table WHERE non_idx_field = 'asdf';

and we wait…

and wait some more.

5GB is not a small table, but this ideally should not take more than a few minutes on a relatively modern system.

iostat is your friend

In cases like this, iostat -x 5 is your friend. While the …

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