Re: Mysql : Completely strange performance behavior
Hi Dominique,
If I understand correctly, the problem turned out to be a different execution plan (use of different index), not replication? If replication is still a problem you will probably get a good answer in the "Replication" subforum.
Regarding 5.5 picking a worse plan: Right after you have imported a huge amount of data on a server, things like cold caches may result in poor performance. This should improve fairly quickly just by throwing the normal queries at the server.
In addition, index statistics may be completely wrong after a huge import. This can be fixed by running ANALYZE TABLE.
If ANALYZE TABLE does not help and you want to keep the index that performed bad for this query, we'll need the following info to provide more assistance:
* SHOW CREATE TABLE for all involved tables
* EXPLAIN for the query in question (both good and bad performing plans would be nice)
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