… main branch yet), and here are the results of my testing of the new Group Commit in Percona Server 5.1. As… Server 5.1.57 with the Group Commit Fix applied. The first graph shows the results when we have a slow fsync… there is also result to compare binary logs enabled and disabled. All results are for binaries with group commit fix. Results with disabled write…
Post: How to find MySQL queries worth optimizing ?
September 11, 2012 By 6 Comments
… matches) but it had to examine 10Mil rows to produce result. What would be good scenario ? – query examining same amount of… which are found and returned up to the top level MySQL part for processing are counted the Rows_examined remains zero… are actually needed to produce group by results. What you can think about in this case is removing group by and aggregate functions…
Post: PHP Large result sets and summary tables.
July 6, 2007 By 8 Comments
… which was done by executing some huge group by query, doing some stuff with results and then populating tables. This all worked… crazy. Why ? Because by default mysql_query uses mysql_store_result C library call and buffers all result set in the process memory. Not… similar behavior. This call users underlying mysql_use_result API call which does not store all result set in memory but instead streams…
Post: Eventual Consistency in MySQL
November 18, 2011 By 8 Comments
….A,Foo.B) WHERE Foo.A IS NULL; If the result set of this query is empty, then there are no… an exclusion-join query for each foreign key relationship: mysql> SELECT CONCAT( ‘SELECT ‘, GROUP_CONCAT(DISTINCT CONCAT(K.CONSTRAINT_NAME, ‘.’, P.COLUMN… result set, it shows us which rows in Bar are orphans. mysql> INSERT INTO Foo (A,B) VALUES (111,2222), (333,444); mysql…
Post: Ultimate MySQL variable and status reference list
January 8, 2011 By 4 Comments
… constantly referring to the amazing MySQL manual, especially the option and variable reference table. But…commanual defaults_extra_fileblogpercona.commanual defaults_fileblogpercona.commanual defaults_group_suffixblogpercona.commanual delay_key_writeblogpercona.commanual Delayed_errorsblogpercona….
Post: Testing MySQL column stores
August 16, 2010 By 15 Comments
… and speed of loading Accuracy of results of queries over the large data set Speed of results of queries over the large… of the queries. ICE supports almost all of the MySQL aggregation functions. Notably, GROUP_CONCAT is not supported, which is something I… higher than it should have been, and several GROUP BY queries returned unexpected results as well. I did not change any “out…
Post: MySQL Indexing Best Practices: Webinar Questions Followup
August 16, 2012 By 4 Comments
…. 2-4 will be evaluated as math expression and the result will be IN(-2) which is not what you’re… mysql use index for group by? A: If you have Index on the column MySQL can avoid temporary table or filesort for group by by this column. This works because by scanning data in index order MySQL…
Post: Scaling problems still exist in MySQL 5.5 and Percona Server 5.5
May 20, 2011 By 11 Comments
…SELECT * FROM table WHERE deleted = 0 AND group_id IN (62715996, 62716592, 62717660, 62717716, 62717722, …core system. For comparison you can checkSysbench Results which Vadim published. For read only …,JOIN::exec,mysql_sel ect,handle_select,execute_sqlcom_select,mysql_execute_command,mysql_parse,…
Post: Fun with the MySQL pager command
January 21, 2013 By 6 Comments
… the result of a command spanning over many lines (for instance SHOW ENGINE INNODB STATUS): mysql> pager less PAGER set to ‘less’ mysql… the result is possible with pager: mysql> pager cat > /dev/null PAGER set to ‘cat > /dev/null’ # Trying an execution plan mysql> SELECT… each status can be done with: mysql> SELECT COMMAND,COUNT(*) TOTAL FROM INFORMATION_SCHEMA.PROCESSLIST GROUP BY COMMAND ORDER BY TOTAL DESC…
Post: Helgrinding MySQL with InnoDB for Synchronisation Errors, Fun and Profit
November 24, 2011 By 2 Comments
… not need much introduction, especially to the MySQL server developers. The Valgrind Memcheck tool, …(fil0fil.c:4432) ==9090== by 0x6B67EDA: log_group_write_buf (log0log.c:1290) ==9090== by… by 0x6A87FC: handle_select(THD*, st_lex*, select_result*, unsigned long) (sql_select.cc:269) ==9090== …
