In my previous post, I’ve showed how to use Dtrace to find queries creating disk temporary tables (only available for OS with dtrace: solaris, freebsd, etc).
In MySQL 5.6 (which is not released yet, use “labs” version for now) we can use new performance_schema table events_statements_history or events_statements_history_long to find all performance metrics for all [...]
Loose index scan in MySQL can really help optimizing “group by” queries in some cases (for example, if you have only min() and/or max() as your aggregate functions). For example, if you have this query (to find maximum delay for all US flights with departure on Sundays in 2010):
select max(DepDelayMinutes), carrier, dayofweek
where dayofweek = [...]
Showed script with Dtrace to find queries creating disk temporary tables [...]
Reporting queries (I will use this term here) are the queries which summaries and groups data over the certain period of time. For example, in Social Network site we want to know how many messages have been sent for the given period of time, group by region and status (sent, received, etc), order by number [...]