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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

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

Recovery deleted ibdata1

August 10, 2012 By Aleksandr Kuzminsky 9 Comments

Recently I had a case when a customer deleted the InnoDB main table space – ibdata1 – and redo logs – ib_logfile*. MySQL keeps InnoDB files open all the time. The following recovery technique is based on this fact and it allowed to salvage the database. Actually, the files were deleted long time ago – [...]

Filed Under: Insight for DBAs, MySQL Tagged With: innodb recovery

On Character Sets and Disappearing Tables

June 21, 2012 By Ernie Souhrada 1 Comment

The MySQL manual tells us that regardless of whether or not we use “SET FOREIGN_KEY_CHECKS=0″ before making schema changes, InnoDB will not allow a column referenced by a foreign key constraint to be modified in such a way that the foreign key will reference a column with a mismatched data type. For instance, if we [...]

Filed Under: Insight for DBAs, MySQL

Percona XtraDB Cluster reference architecture with HaProxy

June 20, 2012 By Peter Boros 63 Comments

This post is a step-by-step guide to set up Percona XtraDB Cluster (PXC) in a virtualized test sandbox. I used Amazon EC2 micro instances, but the content here is applicable for any kind of virtualization technology (for example VirtualBox). The goal is to give step by step instructions, so the setup process is understandable and [...]

Filed Under: MySQL, Percona Software, XtraDB Cluster Tagged With: pxc

Comparing Percona XtraDB Cluster with Semi-Sync replication Cross-WAN

June 14, 2012 By Jay Janssen 7 Comments

I have a customer who is considering Percona XtraDB Cluster (PXC) in a two colo WAN environment. They wanted me to do a test comparing PXC against semi-synchronous replication to see how they stack up against each other. Test Environment The test environment included AWS EC2 nodes in US-East and US-West (Oregon). The ping RTT latency [...]

Filed Under: Benchmarks, MySQL, XtraDB Cluster Tagged With: galera, pxc, semi-sync

Troubleshooting MySQL Memory Usage

March 21, 2012 By Peter Zaitsev 5 Comments

One of the most painful troubleshooting tasks with MySQL is troubleshooting memory usage. The problem usually starts like this – you have configured MySQL to use reasonable global buffers, such as innodb_buffer_size, key_buffer_size etc, you have reasonable amount of connections but yet MySQL takes much more memory than you would expect, causing swapping or other [...]

Filed Under: Insight for DBAs, MySQL

Faster Point In Time Recovery with LVM2 Snaphots and Binary Logs

February 23, 2012 By Jervin Real 3 Comments

LVM snapshots is one powerful way of taking a consistent backup of your MySQL databases – but did you know that you can now restore directly from a snapshot (and binary logs for point in time recovery) in case of that ‘Oops’ moment? Let me show you quickly how. This howto assumes that you already [...]

Filed Under: Insight for DBAs

How to recover deleted rows from an InnoDB Tablespace

February 20, 2012 By Miguel Angel Nieto 4 Comments

In my previous post I explained how it could be possible to recover, on some specific cases, a single table from a full backup in order to save time and make the recovery process more straightforward. Now the scenario is worse because we don’t have a backup or the backup restore process doesn’t work. How [...]

Filed Under: Insight for DBAs, MySQL

The relationship between Innodb Log checkpointing and dirty Buffer pool pages

February 17, 2012 By Jay Janssen 10 Comments

This is a time-honored topic, and there’s no shortage of articles on the topic on this blog. I wanted to write a post trying to condense and clarify those posts, as it has taken me a while to really understand this relationship. Some basic facts Most of us know that writing into Innodb updates buffer [...]

Filed Under: MySQL Tagged With: InnoDB, InnoDB Performance, Tuning

Recovering from a bad UPDATE statement

Recovery after DROP & CREATE

Recovery deleted ibdata1

On Character Sets and Disappearing Tables

Percona XtraDB Cluster reference architecture with HaProxy

Comparing Percona XtraDB Cluster with Semi-Sync replication Cross-WAN

Troubleshooting MySQL Memory Usage

Faster Point In Time Recovery with LVM2 Snaphots and Binary Logs

How to recover deleted rows from an InnoDB Tablespace

The relationship between Innodb Log checkpointing and dirty Buffer pool pages

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