analysis shows single-column indexes on time_stamp speeds stuff up. need to create on appropriate tables.
rev4978 - create time_stamp indexes on 1h and 6h measurement tables to speed up compression / purge intervals;
rev5087 - create time_stamp indexes on raw, 1h, and 6h measurement tables to speed up compression / purge intervals;
QA Closing - code change.
This bug was previously known as http://jira.rhq-project.org/browse/RHQ-2376