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Get rid of wrongly deleted InnoDB tables

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Precaution: Before you try this out on your production system do a BACKUP first! FromDual Backup Manager can help you with this.

Situation

A MySQL user has delete its InnoDB table files for example like this:

shell> rm -f $datadir/test/test.*

Analysis

We do some analysis first:

Switching from MySQL/MyISAM to Galera Cluster

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Switching from MySQL/MyISAM to Galera Cluster requires that all tables (except those from the mysql, information_schema and performance_schema) are using the InnoDB Storage Engine.

For altering the Storage Engine of the tables we wrote a script (alter_engine.pl) long time ago already. Because we have made many of those switches recently we have extended its functionality.

Shrinking InnoDB system tablespace file ibdata1 PoC

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In this weeks MySQL workshop we were discussing, beside other things, about the innodb_file_per_table parameter and its advantages of enabling it. In addition there was a discussion if the InnoDB system tablespace file can be shrinked once it has been grown very large or not. We all know the answer: The InnoDB system tablespace file does never shrink again.

Deadlocks, indexing and Primary Key's

Recently a customer has shown up with some deadlocks occurring frequently. They were of the following type (I have shortened the output a bit):

Ändern von MyISAM Tabellen nach InnoDB und beheben der SELECT COUNT(*) Situation

Es ist ein bekanntes Problem, dass das Ändern der Storage Engine von MyISAM nach InnoDB Probleme verursachen kann [ 1 ], wenn Abfragen der folgenden Art auftreten:

SELECT COUNT(*) from table;

Glücklicherweise kommt dieser Typ von Abfragen selten vor. Und wenn, kann die Abfrage meist einfach weggelassen oder darum herum gearbeitet werden, indem man die Anzahl Zeilen in der Tabelle schätzt. Zum Beispiel mit:

Change MyISAM tables to InnoDB and handle SELECT COUNT(*) situation

Its a known problem that changing the Storage Engine from MyISAM to InnoDB can cause some problems [ 1 ] if you have queries of this type:

SELECT COUNT(*) from table;

Luckily this query happens rarely and if, the query can be easily omitted or worked around by guesstimating the amount of rows in the table. For example with:

Hilft die InnoDB Datenkompression bei wenig Diskplatz?

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Weil wir auf einem unserer Server etwas knapp an Diskplatz sind, hatte ich die Idee, das MySQL Feature Datenkompression für InnoDB auszuprobieren. Dieses Feature ist nützlich, wenn Tabellen mit VARCHAR, BLOB oderr TEXT Attributen vorhanden sind.

Um es nicht allzu einfach zu machen ist unsere Tabelle auch noch partitioniert. Sie sieht wie folgt aus:

Does InnoDB data compression help with short disk space?

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Because we are a bit short off disk space on one of our servers I had the idea to try out the MySQL feature Data Compression for InnoDB. This feature is useful if you have tables with VARCHAR, BLOB or TEXT attributes.

To not make it not too simple our table is partitioned as well. Our table looks like this:

Codership partners with FromDual to offer consulting and support services for Galera Cluster for MySQL

Helsinki, Finland, Uster, Switzerland – February 18, 2012 – Codership, the provider of Galera Cluster for MySQL, and FromDual, a MySQL consulting company, today announced collaboration to offer Galera Cluster technology and related support and consulting services for Galera users all over the world, especially in German speaking countries Germany, Austria and Switzerland (DACH). Galera Cluster is a synchronous, true multi-master replication cluster for MySQL using the well known InnoDB storage engine.

How MySQL behaves with many schemata, tables and partitions

Introduction

Recently a customer claimed that his queries were slow some times and sometimes they were fast.

First idea: Flipping query execution plan caused by InnoDB could be skipped because it affected mainly MyISAM tables.

Second idea: Caching effects by either the file system cache caching MyISAM data or the MyISAM key buffer caching MyISAM indexes were examined: File system cache was huge and MyISAM key buffer was only used up to 25%.

I was a bit puzzled...

Galera - Synchronous Multi-Master Replication Cluster for MySQL/InnoDB

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Galera features

Galera provides the following features:

  • Synchronous replication
  • Active/active multi-master topology
  • Read and write to any cluster node
  • Automatic membership control, failed nodes drop from the cluster
  • Automatic node joining
  • True parallel row level replication
  • Direct client connections
  • Drop-in replacement for native MySQL

Galera benefits

Benefits using Galera Replication:

How good is MySQL INSERT TRIGGER performance

Abstract: In this article we discuss how big is the performance impact of MySQL TRIGGERs compared to application side logging (with INSERT) into a MySQL table.

ER-Diagramm des InnoDB Data Dictionaries

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Mit dem neuen MySQL Release 5.6 sind einige neue InnoDB Data Dictionary Tabellen zum INFORMATION_SCHEMA hinzu gekommen:

Neu in MySQL 5.5 sind:

INNODB_CMP
INNODB_CMP_RESET
INNODB_CMPMEM
INNODB_CMPMEM_RESET
INNODB_TRX
INNODB_LOCK_WAITS
INNODB_LOCKS

Neu in MySQL 5.6 sind:

ER-Diagram of the InnoDB Data Dictionary

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With the new MySQL 5.6 release there are some more InnoDB Data Dictionary Tables in the INFORMATION_SCHEMA:

New with MySQL 5.5 are:

INNODB_CMP
INNODB_CMP_RESET
INNODB_CMPMEM
INNODB_CMPMEM_RESET
INNODB_TRX
INNODB_LOCK_WAITS
INNODB_LOCKS

New with MySQL 5.6 are:

Warming up the InnoDB Buffer Pool during start-up

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Abstract: Heating up the InnoDB Buffer Pool during the MySQL instance startup should significantly improve InnoDB Performance in the beginning of the life of the Instance. This is achieved by sequential scans of the needed data instead of random I/O reads which would happen when we just let the system work it out by itself.
How to find the database objects which can be loaded during MySQL start-up and how to load them automatically is described in this article.

InnoDB Graphs for MySQL Performance Monitor

We have just released v0.7.1 of the FromDual MySQL Performance Monitor. The new release can be downloaded from here.

In all editions some error messages have been cleaned-up, the fall-back data gather method mysql has been removed and the Maria SE template has been renamed to Aria.

In the edition dedicated to our customers most of the InnoDB graphs which are available with MEM v2.3.3 have been implemented now.

How can I find what InnoDB version I am using?

In the old days everything was simpler. We had one maker of our favourite database management system and possibly the choice between different Storage Engines. Mostly the decision has to be taken between MyISAM and InnoDB. When you care about your data integrity you have chosen InnoDB.

Nowadays it is more complex. We have several different makers of our favourite database management system: Oracle/MySQL, Monty Program AB and Percona with their products: MySQL, MariaDB and Percona Server.

Disadvantages of explicitly NOT using InnoDB Primary Keys?

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We recently had the case with one of our customers where we got externally generated random hash values (up to 70 bytes) and they were used as Primary Keys in InnoDB.

As we know, this is not a very good idea because the size of all secondary indexes becomes large and because a random hash value as a Primary Key gives us a bad locality of our rows in the table [ 1 ].

Which table is hit by an InnoDB page corruption?

InnoDB is known to have crash-recovery capabilities and thus is called a crash safe storage engine (in contrary to MyISAM). Never the less under certain circumstances it seems like InnoDB pages can get corrupt during a crash and then a manual crash-recovery is needed.

What is CHECK TABLE doing with InnoDB tables?

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Recently we had a case where a customer got some corrupted blocks in his InnoDB tables. His largest tables where quite big, about 30 to 100 Gbyte. Why he got this corrupted blocks we did not find out yet (disk broken?).

When you have corrupted blocks in InnoDB, it is mandatory to get rid of them again. Otherwise your database can crash suddenly.

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