… you with all the data points you need to attack the right query in the right way. But vanilla MySQL does have… log all the extra stats I mentioned above in the overview section. So say if you were using the vanilla MySQL server… 2.5% 51 0.0039 1.00 0.00 SELECT UNION wp_pp_daily_summary wp_pp_hourly_summary wp_pp…
Post: Identifying the load with the help of pt-query-digest and Percona Server
December 29, 2011 By 3 Comments
Post: The Optimization That (Often) Isn't: Index Merge Intersection
December 14, 2012 By 6 Comments
… clauses with columns that had single-column indexes on them, MySQL could sometimes make use of the multiple indexes. For instance… = X OR indexed_colB = Y” might use the index merge union algorithm, which would *simultaneously* (this is important, as we will… be satisfied in some other way. After all, if an index isn’t there, MySQL can’t attempt to use it, but…
Post: Distributed Set Processing with Shard-Query
May 14, 2011 By 27 Comments
… as a materialized view over a union of all the already joined and aggregated data from all the nodes. A single temporary table…. This allows BETWEEN, IN, subqueries in the FROM clause, and UNION operations to operate fully in parallel. Distributed set processing is… of compute resource which speaks SQL, but right now only MySQL storage nodes are supported. Amdahl’s law applies to the…
Comment: Possible optimization for sort_merge and UNION ORDER BY LIMIT
October 5, 2007 By 10 Comments
[...] I was comparing performance of UNION vs MySQL 5.0 index merge algorithm Sinisa pointed out I should be using UNION ALL instead of simple UNION in my benchmarks, and he was [...]
Post: How is join_buffer_size allocated?
July 5, 2010 By 9 Comments
When examining MySQL configuration, we quite often want to know how various buffer …s been determined to be needed. And it’s allocated all at once. So a 128M join_buffer_size is indeed… << 30; # 1GB select * from (select 1 union select 1) as x1 join (select 1 union select 1) as x2 join…. That should…
Comment: UNION vs UNION ALL Performance
December 5, 2007 By 15 Comments
[...] Warum? UNION vs UNION ALL Performance | MySQL Performance Blog __________________ Siste gradum teque aspectu ne subtrahe nostro! Quem fugis? Extremum fato, quod [...]
Comment: UNION vs UNION ALL Performance
October 12, 2007 By 15 Comments
[...] Peter Zaitsev of the MySQL Performance Blog compares the performance of UNION vs. UNION ALL. [...]
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… does not work for subselects, inline views, parts of the UNION. This is also common missunderstanding. Works on packet level – This… result set but MySQL has no way to identify which one of them would so it gets rid of all of them…
Post: SQL Injection Questions Followup
July 26, 2012 By 2 Comments
…too much computation load onto their database server. Their MySQL server became CPU-bound, while their multiple PHP … more difficult part is making sure to test for all such cases in your code where SQL statements …name of a Mr. Order, who lives at 123 Union Street? If you are careful to escape or …
Post: MySQL: Data Storage or Data Processing
November 18, 2007 By 9 Comments
… lot of other personalized services they may not use MySQL (and SQL at all). In many cases you would see absolutely custom… jobs such as sorting, unions/instersections have to be performed on the SQL node. May be MySQL Cluster will evolve and data storage nodes will be able to perform all kinds of operations, in…
