Wednesday, February 9, 2011

Query of death

FRED continues to have short periods of downtime ranging from 3-6 minutes a few times per week. These appear to be caused by a request that runs a very expensive query that takes a couple minutes to run and consumes most of the database's resources during that time. This slows or blocks other users' queries, causing page requests to stack up and take all of the available memory on the web server, subsequently causing all pages to fail to load.

I'm looking at how to prevent that query from occurring. It may actually be triggered by a search engine crawler (hence FRED not being built for its behavior, and failing to handle it).

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