…Query over Hive is that it works with existing MySQL data sets and queries. Another advantage is that it works with all MySQL…query: BETWEEN or IN clauses, subqueries in the FROM clause, UNION or UNION…
Post: Identifying the load with the help of pt-query-digest and Percona Server
December 29, 2011 By 3 Comments
… 0, because otherwise you can have a really large log file generated. Another thing that we normally…% 51 0.0039 1.00 0.00 SELECT UNION wp_pp_daily_summary wp_pp_hourly_summary …queries that you can use to gather more data about the underlying tables involved and the query execution plan used by MySQL…
Post: MySQL: Followup on UNION for query optimization, Query profiling
August 14, 2006 By 12 Comments
… way so you do not have to use the union. So changing query to: mysql> SELECT sql_no_cache name FROM people WHERE… are large. Take 3 IN lists 1000 values each, on appropriate 3 keyparts and you may finish your lunch before query completes… you can profile queries to see what exactly happens during query execution – very helpful for MySQL Performance optimization: mysql> flush status; Query OK, 0 rows…
Post: MySQL Query Cache
July 27, 2006 By 69 Comments
…query_cache_wlock_invalidate=ON. Caching full queries only – Meaning it does not work for subselects, inline views, parts of the UNION…query cache. Now lets speak a bit about Query Cache configuration and mainance. MySQL Manual is pretty good on this: Query Cache Query Cache Status Query…
Post: MySQL: Data Storage or Data Processing
November 18, 2007 By 9 Comments
…memcache) is often implemented to offload MySQL. When it comes to large scale data processing other techniques are… not take you that far. MySQL concept of Single Query=Single Thread works well when few … sorting, unions/instersections have to be performed on the SQL node. May be MySQL Cluster will …
Post: How adding another table to JOIN can improve performance ?
August 1, 2008 By 12 Comments
… or UNION which however require rather serious application changes and also can result in huge IN lists and suboptimal execution for large… us now replace the range with IN list in this query: mysql> explain select sum(events) from info where d IN(’2007… say thousands of groups at the same time ? Performing such query MySQL has to build (and do lookups) for all combinations which…
Post: Multi Column indexes vs Index Merge
September 19, 2009 By 30 Comments
…MySQL puts i1 and combined into “possible_key” while it has no way to use them for this query. The query…. This reflects very large performance difference between…,4 | NULL | 299364 | Using sort_union(i1,i2); Using where | …
Post: ORDER BY ... LIMIT Performance Optimization
September 1, 2006 By 93 Comments
…standpoint (even though a bit ugly) will be UNION workaround I already wrote about. So what if…LIMIT. However if you’re dealing with LIMIT query with large offset efficiency will suffer. LIMIT 1000,…in slow query log as query which does not use indexes, even if it is quite fast: mysql> explain select…
Post: Multiple column index vs multiple indexes
August 22, 2008 By 13 Comments
… of starting MySQL etc from equation I also measured execution of “SELECT 1″ query using same … to show what difference large BETWEEN can make. Conclusion: For benchmarked queries we can see Multiple … watchout a MySQL may decide not to do Index merge (either intersection or union) but instead …
