October 30, 2014

Recover orphaned InnoDB partition tablespaces in MySQL

A few months back, Michael wrote about reconnecting orphaned *.ibd files using MySQL 5.6. I will show you the same procedure, this time for partitioned tables. An InnoDB partition is also a self-contained tablespace in itself so you can use the same method described in the previous post. To begin with, I have an example […]

Innodb redo log archiving

Percona Server 5.6.11-60.3 introduces a new “log archiving” feature. Percona XtraBackup 2.1.5 supports “apply archived logs.” What does it mean and how it can be used? Percona products propose three kinds of incremental backups. The first is full scan of data files and comparison the data with backup data to find some delta. This approach […]

InnoDB performance optimization basics (redux)

I recently stumbled upon a post that Peter Zaitsev published back in 2007 titled “Innodb Performance Optimization Basics.” It’s a great post and reading it inspired me to examine what’s changed in the nearly six years that have followed in terms of MySQL, Percona Server – as well as in all of the other now-available […]

How to move the InnoDB log sequence number (LSN) forward

This post focuses on the problem of the InnoDB log sequence number being in the future. Preface: What is an InnoDB log sequence number? The Log sequence number (LSN) is an important database parameter used by InnoDB in many places. The most important use is for crash recovery and buffer pool purge control. Internally, the InnoDB […]

Checking B+tree leaf nodes list consistency in InnoDB

If we have InnoDB pages there are two ways to learn how many records they contain: PAGE_N_RECS field in the page header Count records while walking over the list of records from infimum to supremum In some previous revision of the recovery tool a short summary was added to a dump which is produced by […]

How to recover table structure from InnoDB dictionary

To recover a dropped or corrupt table with Percona Data Recovery Tool for InnoDB you need two things: media with records(ibdata1, *.ibd, disk image, etc.) and a table structure. Indeed, there is no information about the table structure in an InnoDB page. Normally we either recover the structure from .frm files or take it from […]

Recovery after DROP & CREATE

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”:

If there were no subsequent CREATE TABLE the recovery would be trivial. Index_id of the PRIMARY index of […]

Recovery deleted ibdata1

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 – […]

On Character Sets and Disappearing Tables

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 […]

Faster Point In Time Recovery with LVM2 Snaphots and Binary Logs

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 […]