Hi Jack,
It is not surprising that the performance decreases for queries run concurrently with a long-running query. There are all sorts of issues that may be involved:
For example:
* The simple queries have to share hardware resources with the long running query
* There may be concurreny issues like locking conflicts between the queries.
I think the first step is to figure out if we can do anything to improve performance of the long-running query. To do that we need:
* MySQL version
* SHOW CREATE table -- for all involved tables
* An estimate of the number of rows in each of these tables
* EXPLAIN SELECT -- for the long-running query
Hope this helps,
Jørgen Løland
Software Engineer, MySQL, Oracle
jorgenloland.blogspot.com