Analysis of InnoDB adaptive hash index parameter for sysbench

As I mentioned in a previous blog post I was suspicious that the
adaptive hash index in InnoDB added to the scalability issues in
the MySQL Server. So I decided to run a test where I disabled the
adaptive hash index.

The results were fairly much as expected. The adaptive hash
index usage improves performance on low thread counts
(up to about 16) by a few percent. However at 32 threads and
beyond the performance is better without the adaptive hash
index and equal in some cases. In particular the top performance
goes up by about 3% when this is disabled.

This confirms the documentation in the InnoDB manual that the
adaptive hash index improves performance as long as the lock
around it doesn't hurt performance. So for the majority of users
it's a good idea to have it turned on, but for users with high-end
servers it's a good idea to test if turning it off will improve
performance.

For sysbench benchmarks it's clearly a good idea to turn it off.