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Message Posted: Wed, 09 Jan 2008 @ 13:17:14 GMT

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Subj:   Re: Impact of a Heartbeat Query
From:   fachtna.c.donovan


We run a heartbeat query on the hour every hour 24/7 365 on our Production, Backup and Development machines.

The query takes anything from about 30 seconds to over an hour depending on how busy the machine is (avg about 2 mins) but we find it a useful metric to measure how busy the machine is and to spot for possible performance impacts.

The query that we run is a perfect example of how NOT to write SQL, a few unions and cross joins of two 1000 row tables and some inefficient ranking functions put in for good measure. If you have a a query that runs in 1 sec on a quite machine and 5 sec on a busy machine you can't really tell that the machine is running 5 times slower, so we wanted a query that ran a bit slower when the machine was quite and for a while when the machine is busy.

We think that the impact of this query running every hour is worth it for the metricĀ's that we can get from the results.

Hope this helps.

Fachtna O'Donovan
Software Engineer
AIB Bank

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