benoit, 
Recently I worked a lot on performance issue on a #PostgreSQL db. Few things to remember.
- Learn to read explain + use tools like the one from Dalibo
- Planner can take wrong decisions
- Create a snapshot with production data and tests index/settings/etc
- Use psql
- When testing indexes, remove the one used to see if the new one is used
- PgAnalyze is a good tool
- Keep a logbook of your work
- Write a script with the queries that should be fast
1/2
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