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Recovering from a bad UPDATE statement

October 19, 2012 By Michael Coburn 5 Comments

Did you just run an UPDATE against your 10 million row users table without a WHERE clause? Did you know that in MySQL 5.5 that sometimes you can recover from a bad UPDATE statement? This is possible if you are running in binlog_format=ROW ! Imagine this scenario:

CREATE TABLE `t1` (
 `c1` int(11) NOT NULL AUTO_INCREMENT,
 `c2` varchar(10) NOT NULL,
 PRIMARY KEY (`c1`)
) ENGINE=InnoDB;
INSERT INTO `t1` (`c2`) VALUES ('michael'), ('peter'), ('aamina');

CREATE TABLE `t1` (

`c1` int(11) NOT NULL AUTO_INCREMENT,

`c2` varchar(10) NOT NULL,

PRIMARY KEY (`c1`)

) ENGINE=InnoDB;

INSERT INTO `t1` (`c2`) VALUES ('michael'), ('peter'), ('aamina');

We run an accidental UPDATE statement that [...]

Filed Under: Insight for DBAs, Insight for Developers, MySQL

When is MIN(DATE) != MIN(DATE) ?

September 4, 2012 By Ernie Souhrada 5 Comments

Inspiration for this post is courtesy of a friend and former colleague of mine, Greg Youngblood, who pinged me last week with an interesting MySQL puzzle. He was running Percona Server 5.5.21 with a table structure that looks something like this:

CREATE TABLE foo (
 id INT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
 uid INT UNSIGNED NOT NULL,
 update_time DATETIME NOT NULL,
 ....
 INDEX `uid` (uid, update_time),
 INDEX `bar` (some_other_columns)
 ....
) ENGINE=InnoDB;

CREATE TABLE foo (

id INT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,

uid INT UNSIGNED NOT NULL,

update_time DATETIME NOT NULL,

....

INDEX `uid` (uid, update_time),

INDEX `bar` (some_other_columns)

....

) ENGINE=InnoDB;

When he ran this query:

SELECT MIN(update_time) FROM foo WHERE update_time IS NOT NULL AND update_time <> '0000-00-00 00:00:00';

1	SELECT MIN(update_time) FROM foo WHERE update_time IS NOT NULL AND update_time <> '0000-00-00 00:00:00';

The result came back as 2012-06-22 10:28:16. [...]

Filed Under: Insight for DBAs, Insight for Developers, MySQL

Announcing Percona Server 5.5.27-28.0

August 23, 2012 By Hrvoje Matijakovic 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 [...]

Filed Under: MySQL

Recovery after DROP & CREATE

August 22, 2012 By Aleksandr Kuzminsky 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”:

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 */;

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 [...]

Filed Under: MySQL Tagged With: drop table, InnoDB, Recovery

Percona XtraDB Cluster: Multi-node writing and Unexpected deadlocks

August 17, 2012 By Jay Janssen 17 Comments

Percona XtraDB Cluster (PXC) and the technology it uses (Galera) is an exciting alternative to traditional MySQL replication. For those who don’t know, it gives you: Fully Synchronous replication with a write latency increase equivalent to a ping RTT to the furthest node Automatic cluster synchronization, both incremental and full restores The ability to read [...]

Filed Under: MySQL, XtraDB Cluster

ALTER TABLE: Creating Index by Sort and Buffer Pool Size

June 27, 2012 By Peter Zaitsev 4 Comments

Today I was looking at the ALTER TABLE performance with fast index creation and without it with different buffer pool sizes. Results are pretty interesting. I used modified Sysbench table for these tests because original table as initially created only has index on column K which initially contains only zeros, which means index is very [...]

Filed Under: Insight for DBAs, MySQL

DROP TABLE and stalls: Lazy Drop Table in Percona Server and the new fixes in MySQL

June 22, 2012 By Ovais Tariq 33 Comments

Suppose you have turned on innodb_file_per_table (which means that each table has its own tablespace), and you have to drop tables in a background every hour or every day. If its once every day then you can probably schedule the table dropping process to run during off-peak hours. But I have seen cases where the [...]

Filed Under: Benchmarks, Insight for DBAs, MySQL

Benchmarking single-row insert performance on Amazon EC2

May 16, 2012 By Ovais Tariq 17 Comments

I have been working for a customer benchmarking insert performance on Amazon EC2, and I have some interesting results that I wanted to share. I used a nice and effective tool iiBench which has been developed by Tokutek. Though the “1 billion row insert challenge” for which this tool was originally built is long over, [...]

Filed Under: Benchmarks, Insight for DBAs, MySQL Tagged With: Benchmarks, ec2, iiBench, insert performance, partitioning, Secondary indexes, write performance

STOP: DELETE IGNORE on Tables with Foreign Keys Can Break Replication

February 2, 2012 By Jervin Real 1 Comment

DELETE IGNORE suppresses errors and downgrades them as warnings, if you are not aware how IGNORE behaves on tables with FOREIGN KEYs, you could be in for a surprise. Let’s take a table with data as example, column c1 on table t2 references column c1 on table t1 – both columns have identical set of rows for [...]

Filed Under: Insight for DBAs

Percona testing: Quick test clusters with kewpie!

January 13, 2012 By patrick.crews Leave a Comment

The announcement of Percona XtraDB Cluster seems to have generated a fair bit of interest : ) Although the documentation contains more formal instructions for setting up a test cluster, I wanted to share a quick way to set up an ad-hoc cluster on a single machine to help people play with this (imho) rather [...]

Filed Under: Benchmarks, MySQL

Recovering from a bad UPDATE statement

When is MIN(DATE) != MIN(DATE) ?

Announcing Percona Server 5.5.27-28.0

Recovery after DROP & CREATE

Percona XtraDB Cluster: Multi-node writing and Unexpected deadlocks

ALTER TABLE: Creating Index by Sort and Buffer Pool Size

DROP TABLE and stalls: Lazy Drop Table in Percona Server and the new fixes in MySQL

Benchmarking single-row insert performance on Amazon EC2

STOP: DELETE IGNORE on Tables with Foreign Keys Can Break Replication

Percona testing: Quick test clusters with kewpie!

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