Prior to version 5.0, MySQL could only use one index per table in a given query without any exceptions; folks that didn’t understand this limitation would often have tables with lots of single-column indexes on columns which commonly appeared in their WHERE clauses, and they’d wonder why the EXPLAIN plan for a given SELECT would [...]
Announcing Percona Server 5.5.28-29.2
December 7, 2012 By 2 Comments
Percona is glad to announce the release of Percona Server 5.5.28-29.2 on December 7th, 2012 (Downloads are available here and from the Percona Software Repositories). Based on MySQL 5.5.28, including all the bug fixes in it, Percona Server 5.5.28-29.2 is now the current stable release in the 5.5 series. All of Percona‘s software is open-source and free, all the details of the release can [...]
Quickly finding unused indexes (and estimating their size)
December 5, 2012 By 2 Comments
I had a customer recently who needed to reduce their database size on disk quickly without a lot of messy schema redesign and application recoding. They didn’t want to drop any actual data, and their index usage was fairly high, so we decided to look for unused indexes that could be removed. Collecting data It’s [...]
Knowing what pt-online-schema-change will do
November 1, 2012 By 1 Comment
pt-online-schema-change is simple to use, but internally it is complex. Baron’s webinar about pt-online-schema-change hinted at several of the tool’s complexities. Consequently, users often want to know before making changes what pt-online-schema-change will do when it runs. The tool has two options to help answer this question: –dry-run and –print. When ran with –dry-run and –print, pt-online-schema-change changes nothing [...]
Announcing Percona Server 5.5.27-28.0
August 23, 2012 By 5 Comments
Percona is glad to announce the release of Percona Server 5.5.27-28.0 on August 23rd, 2012 (Downloads are available here and from the Percona Software Repositories). Based on MySQL 5.5.27, including all the bug fixes in it, Percona Server 5.5.27-28.0 is now the current stable release in the 5.5 series. All of Percona‘s software is open-source and free, all the details of the release can [...]
Recovery after DROP & CREATE
August 22, 2012 By 1 Comment
In a very popular data loss scenario a table is dropped and empty one is created with the same name. This is because mysqldump in many cases generates the “DROP TABLE” instruction before the “CREATE TABLE”:
1 2 3 4 5 6 7 8 9 10 11 12 | DROP TABLE IF EXISTS `actor`; /*!40101 SET @saved_cs_client = @@character_set_client */; /*!40101 SET character_set_client = utf8 */; CREATE TABLE `actor` ( `actor_id` smallint(5) unsigned NOT NULL AUTO_INCREMENT, `first_name` varchar(45) NOT NULL, `last_name` varchar(45) NOT NULL, `last_update` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP, PRIMARY KEY (`actor_id`), KEY `idx_actor_last_name` (`last_name`) ) ENGINE=InnoDB AUTO_INCREMENT=201 DEFAULT CHARSET=utf8; /*!40101 SET character_set_client = @saved_cs_client */; |
If there were no subsequent CREATE TABLE the recovery would be trivial. Index_id of the PRIMARY index of [...]
Innodb Table Locks
July 31, 2012 By 4 Comments
Innodb uses row level locks right ? So if you see locked tables reported in SHOW ENGINE INNODB STATUS you might be confused and rightfully so as Innodb table locking is a bit more complicated than traditional MyISAM table locks. Let me start with some examples. First lets run SELECT Query:
1 2 3 4 5 | ---TRANSACTION 12303, ACTIVE 26 sec mysql tables in use 2, locked 0 MySQL thread id 53038, OS thread handle 0x7ff759b22700, query id 3918786 localhost root Sending data select count(*) from sbtest,sbtest x Trx read view will not see trx with id >= 12304, sees < 12301 |
As you can [...]
Impact of memory allocators on MySQL performance
July 5, 2012 By 11 Comments
MySQL server intensively uses dynamic memory allocation so a good choice of memory allocator is quite important for the proper utilization of CPU/RAM resources. Efficient memory allocator should help to improve scalability, increase throughput and keep memory footprint under the control. In this post I’m going to check impact of several memory allocators on the [...]
Find unused indexes
June 30, 2012 By Leave a Comment
I wrote one week ago about how to find duplicate indexes. This time we’ll learn how to find unused indexes to continue improving our schema and the overall performance. There are different possibilites and we’ll explore the two most common here. User Statistics from Percona Server and pt-index-usage. User Statistics User Statistics is an improvement [...]
MySQL Upgrade Webinar Questions Followup
June 28, 2012 By 7 Comments
I did a Webinar about MySQL Upgrade – Best Practices Yesterday and there were some questions we could not answer during Webinar, following Jay’s Lead I decided to post them as a Blog Post. Q: Can you go directly MySQL 5.0 to 5.5 for MyISAM tables? MyISAM have not been getting any significant development since [...]
