…in main memory. Each row is on the order of 30 bytes in the primary table, and…starts hitting disk. Perhaps you could verify that by watching IOstat. Tim’s measurements (http://www.tokutek…mdcallag/mysql-patch/mytools/annotate/head%3A/bench/ibench/iibench.py) is that it measures query performance too,…
Post: Join Optimizations in MySQL 5.6 and MariaDB 5.5
April 4, 2012 By 2 Comments
…-ordered scan, the secondary key on col1 would be sorted by col1 i.e. in index order and then the lookup will be performed. So key-ordered scan is basically… a look at the status counters. Counter Name MySQL 5.5 MySQL 5.6 MySQL 5.6 w/ join_buffer_size=6M & read…
Post: Multi Range Read (MRR) in MySQL 5.6 and MariaDB 5.5
March 21, 2012 By 10 Comments
… key_column, pk_column FROM tbl WHERE key_column=x ORDER BY key_column (Note that secondary keys in InnoDB contain primary… = n_nationkey group by c_custkey, c_name, c_acctbal, c_phone, n_name, c_address, c_comment order by revenue desc LIMIT… were captured when performing the benchmark on IO bound workload, mentioned above. Counter Name MySQL 5.5 MySQL 5.6 MySQL 5.6 w…
Post: InnoDB's gap locks
March 27, 2012 By 15 Comments
…, InnoDB locks all index records found by the WHERE clause with an …transactions affecting the concurrency and the performance you can disable them in two … reads (non repeatable reads) so in order to prevent problems with the …en/innodb-locks-set.html. Conclusion MySQL uses REPEATABLE READ as the …
Post: ORDER BY ... LIMIT Performance Optimization
September 1, 2006 By 93 Comments
Suboptimal ORDER BY implementation, especially together with LIMIT is often the cause of MySQL Performance problems. Here is what you need to know about ORDER BY … LIMIT optimization to avoid these problems ORDER BY with LIMIT…
Post: Flexviews - part 3 - improving query performance using materialized views
April 4, 2011 By 12 Comments
… ‘> order by total_price desc; ‘> ‘); Query OK, 1 row affected (0.00 sec) When the view is ‘enabled’, the contents are created: mysql… with the incremental method, like ORDER BY or use of NOW(), it but still provides improved performance during refresh by accessing summarized data. I…
Post: MySQL Performance - eliminating ORDER BY function
October 17, 2007 By 6 Comments
… rules you would learn about MySQL Performance Optimization is to avoid using functions when comparing constants or order by. Ie use indexed_col=N… which sorts by function is able to avoid order by while second which uses direct column value needs to do the filesort: mysql> explain select * from tst where i=5 and date(d)=date(now()) order by date(d) \G *************************** 1…
Post: Possible optimization for sort_merge and UNION ORDER BY LIMIT
September 18, 2007 By 10 Comments
… need to perform sort results retrieved from MySQL when your WHERE clause goes beyound col=const values which would allow MySQL to still… add ORDER BY ORD LIMIT 10 to individual queries. What if we do int manually ? mysql> explain (select * from utest where c1=5 order by ord desc limit 10) union (select * from utest where c2=5 order by ord…
Post: Eventual Consistency in MySQL
November 18, 2011 By 8 Comments
… that the enforcement of foreign keys incurs a significant performance overhead.1,2 MySQL allows us to set FOREIGN_KEY_CHECKS=0…, ‘.’, K.COLUMN_NAME) ORDER BY K.ORDINAL_POSITION), ‘) = (‘, GROUP_CONCAT(CONCAT(K.REFERENCED_TABLE_NAME, ‘.’, K.REFERENCED_COLUMN_NAME) ORDER BY K.ORDINAL_POSITION…
Post: Performance Schema tables stats
May 2, 2011 By 2 Comments
… to get from performance schema tables. 1. table_io_waits_summary_by_table mysql> select * from table_io_waits_summary_by_table where OBJECT… can get top tables that required read IO mysql> select * from file_summary_by_instance order by COUNT_READ desc limit 6G *************************** 1. row…
