… used as the underlying storage for the virtual machines. Baseline: The MySQL command line client was used … of this data set in a previous blog post. Previous testing was limited to a subset … the FROM clause, UNION or UNION ALL clauses. If none of those features are used, then parallelism can’…
Post: MySQL Query Cache
July 27, 2006 By 70 Comments
… great feature called “Query Cache” which is quite helpful for MySQL Performance optimization tasks but there are number of things you… of the UNION. This is also common missunderstanding. Works on packet level – This is one of the reason for previous item. Query… is good idea to use query cache ? Third party application – You can’t change how it works with MySQL to add caching…
Post: The Optimization That (Often) Isn't: Index Merge Intersection
December 14, 2012 By 6 Comments
… WHERE indexed_colA = X OR indexed_colB = Y” might use the index merge union algorithm, which would *simultaneously* (this is important, as…_colA and indexed_colB and then do a set-theoretic union of the two result sets. Replace that “OR” with an…’t there, MySQL can’t attempt to use it, but this has the same challenges that are present with the previous solution. What…
Post: MySQL Indexing Best Practices: Webinar Questions Followup
August 16, 2012 By 4 Comments
…use something like Trick “Unionizing Order by” described in presentation. Q: what is the impact on indexing to use… Q: how mysql use index for group by? A: If you have Index on the column MySQL can …list – each leaf page contains pointers to both previous and next pages in index order. Note however…
Post: Distributed Set Processing with Shard-Query
May 14, 2011 By 27 Comments
… asked this question in comments to to my previous Shard-Query benchmark. Actually he asked if it…union of all the already joined and aggregated data from all the nodes. A single temporary table is used…resource which speaks SQL, but right now only MySQL storage nodes are supported. Amdahl’s law …
Post: How adding another table to JOIN can improve performance ?
August 1, 2008 By 12 Comments
… issue with MySQL optimizer stopping using further index key parts as soon as there is a range clause on the previous key part… described couple of solutions to this problem – using IN list instead of range or UNION which however require rather serious application changes… newer MySQL versions will stop using this optimization method if there are too many combinations to check). Instead you could use JOIN to…
Post: ORDER BY ... LIMIT Performance Optimization
September 1, 2006 By 100 Comments
… LIMIT 10; Even though it looks quite similar to previous one it is a lot different as there are… performance standpoint (even though a bit ugly) will be UNION workaround I already wrote about. So what if you … is possible to use index to do ORDER BY with JOIN MySQL still will not be able to use it as…
Post: Multiple column index vs multiple indexes
August 22, 2008 By 13 Comments
After my previous post there were questions raised about Index Merge on Multiple … of low cardinality even though MySQL can’t use index well. You’re right MySQL can’t and MySQL does not – Full table scan… can be used. It is also worth to watchout a MySQL may decide not to do Index merge (either intersection or union) but…
