MariaDB 5.3/5.5 has introduced a new join type “Hash Joins” which is an implementation of a Classic Block-based Hash Join Algorithm. In this post we will see what the Hash Join is, how it works and for what types of queries would it be the right choice. I will show the results of executing benchmarks [...]
InnoDB’s gap locks
March 27, 2012 By 15 Comments
One of the most important features of InnoDB is the row level locking. This feature provides better concurrency under heavy write load but needs additional precautions to avoid phantom reads and to get a consistent Statement based replication. To accomplish that, row level locking databases also acquire gap locks. What is a Phantom Read A [...]
Identifying the load with the help of pt-query-digest and Percona Server
December 29, 2011 By 3 Comments
Overview Profiling, analyzing and then fixing queries is likely the most oft-repeated part of a job of a DBA and one that keeps evolving, as new features are added to the application new queries pop up that need to be analyzed and fixed. And there are not too many tools out there that can make [...]
Debugging problems with row based replication
May 6, 2010 By 12 Comments
MySQL 5.1 introduces row based binary logging. In fact, the default binary logging format in GA versions of MySQL 5.1 is ‘MIXED’ STATEMENT*; The binlog_format variable can still be changed per sessions which means it is possible that some of your binary log entries will be written in a row-based fashion instead of the [...]
How Percona does a MySQL Performance Audit
November 24, 2008 By 17 Comments
Our customers or prospective customers often ask us how we do a performance audit (it’s our most popular service). I thought I should write a blog post that will both answer their question, so I can just reply “read all about it at this URL” and share our methodology with readers a little bit. This [...]
Data Recovery Toolkit for InnoDB Version 0.1 Released
November 26, 2007 By 6 Comments
As Peter mentioned in one of previous posts, we’ve done huge work developing robust strategies of InnoDB data recovery to provide our customers effective data recovery services and one of major parts of these strategies is our toolkit for InnoDB data recovery. Today I’m proud to announce its first public release which was used to [...]
MySQL: Followup on UNION for query optimization, Query profiling
August 14, 2006 By 14 Comments
Few days ago I wrote an article about using UNION to implement loose index scan. First I should mention double IN also works same way so you do not have to use the union. So changing query to:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 | mysql> SELECT sql_no_cache name FROM people WHERE age in(18,19,20) AND zip IN (12345,12346, 12347); +----------------------------------+ | name | +----------------------------------+ | ed4481336eb9adca222fd404fa15658e | | 888ba838661aff00bbbce114a2a22423 | +----------------------------------+ 2 rows in set (0.00 sec) mysql> explain SELECT sql_no_cache name FROM people WHERE age in(18,19,20) AND zip IN (12345,12346, 12347); +----+-------------+--------+-------+---------------+------+---------+------+------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+--------+-------+---------------+------+---------+------+------+-------------+ | 1 | SIMPLE | people | range | age | age | 4 | NULL | 9 | Using where | +----+-------------+--------+-------+---------------+------+---------+------+------+-------------+ 1 row in set (0.00 sec) |
So as you see there are really different types of ranges in MySQL. IN range allows [...]
