Re: Repeated Query Execution - Strange Behavior

[Peter Zaitsev]

If your box is not getting any other load this looks pretty strange. Performance quite frequently increases after first run because of caches warmed up but it would be strange for it to be dropping.

It could be there is some non-deterministic behavior somewhere which makes MySQL to select different plans for query execution.

You can check this by doing following for each query run:

run "FLUSH STATUS";
execute query
run "SHOW STATUS" and save result.

Later compare SHOW STATUS results for runs you've done - they should be be
same or very close if query is executed the same way.

You can also try running EXPLAIN <query> and check if there are any changes for it.