So where I'm working, a performance issue was identified that affected many functions, because the (SQL language) functions took an int argument used it in a where clause against a column (config_id) that was stored in varchar format, leading to an inefficient casting when the query was parameterized. We could work around that with (select $3::text) instead of just $3, but since the data is actually all numbers under 65k, we altered the data type of the column to smallint, rather than editing a boatload of functions with a hacky workaround.
For most functions, this fixed the problem.
However, it had a drastically-negative impact on the query in question, which was originally taking 2 minutes, 45 seconds. After adding a couple indexes with the config_id still as a varchar, that time is reduced down to 42 seconds. However when the data type is smallint, the query runs for many hours - I let it run for 4.5 hours yesterday before cancelling it.
It's pretty clear that the planner is making horrid misestimates and picking a terrible plan. I would appreciate any advice for getting this into a better state.
Here are the explain plans:
When config_id is a varchar, it executes in 42 seconds:
When config_id is a smallint, it runs too long to allow to complete, but clearly the plan is bad:
Here is the query, along with rowcounts and schema of every table involved in the query:
PostgreSQL version is 8.4, and most of our GUC's are default.
Thanks in advance for any suggestions.
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Casey Allen Shobe
casey@shobe.info