Hi,
We've had a similar problem (duplicate keys under low stress test). It was solved by switching all tables to InnoDB engine.
Our problems occured when using pure MyIsam (default on *nix) or combinations of MyIsam and InnoDB. The issue was only resolved when using pure InnoDB.
Obviously InnoDB and MyIsam have other advantages/weaknesses. But because of this, we now feel forced to only use InnoDB.
Hope this helps.
Regards,
Jesse van Houten
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