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Comment by davidyeager | Hacker News Reader

This does not rewrite your database. It optimizes the live in-memory machine code of the mysqld (MySQL Server) process. It must run on the same OS host as the mysqld (MySQL Server) process being optimized. So if you are using this on the master and not on the replica, the replica won’t be touched. Hope that makes sense.

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I think the point was that profile guided optimization relies on the workload staying relatively fixed. If the workload suddenly changes (like promoting a readonly slave to be the writable master) the assumptions made by PGO may not be valid, and performance could be worse than if no modifications were made in the first place.

I think you'd just have to measure scenarios before using it in production.

Dynimizer can react to drastic changes in workload and reoptimize depending on how you configure it.

grogers explained my intent well, especially around the promotion of a replica to a primary work load (thank you). I think we're arguing semantics between optimizing machine code and rewriting mysqld. I want to emphasize that Dynamizer looks super awesome, and I do intend to try it, so no offense was intended. Well done!

Thanks! Sorry for terse tone... just responding quickly from a smartphone while travelling :-) Your concerns are definitely valid and we are working on improving the situation.

Dynimizer can detect a drastic workload change as you described and reoptimize in response. That’s the default operation which can be turned off. What has been observed is that if we optimized for say a write-heavy workload and then change it to read-only without reoptimizing (or vice versa), it will still show an improvement, just not as much. Hope that makes sense.

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