Andgus,
I have tested the scalability on a dual-core cpu and the behaviour is bad - the plugin has negative scalability.
1 thread:
Requests per second: 5.29 [#/sec] (mean)
2 threads:
Requests per second: 6.43 [#/sec] (mean)
4 threads:
Requests per second: 6.85 [#/sec] (mean)
8 threads:
Requests per second: 6.41 [#/sec] (mean)
16 threads:
Requests per second: 4.01 [#/sec] (mean)
32 threads:
Requests per second: 3.63 [#/sec] (mean)
These results above are from apachebench calling php script, thus if you use direct connections to mysqld, the result might be even worse.
When I run these queries to the searchd directly, the scalability is OK.