The unDROP for InnoDB tool can be used to recover corrupt MySQL database. In this post we will show how to repair MySQL database if its files became corrupted and even innodb_force_recovery=6 doesn’t help.

The corruption of InnoDB tablespace may be caused by many reasons. A dying hard drive can write garbage, thus page checksum will be wrong. InnoDB then reports to the error log:

InnoDB: Database page corruption on disk or a failed
InnoDB: file read of page 4.

MySQL is well know for poor start-up script. A simple upgrade procedure may end up with two mysqld processes writing to the same tablespace. That leads to the corruption too. Sometimes power reset corrupts not only InnoDB files, but file system becomes unusable for the operating system.

InnoDB …

Percona Server version 5.1.73-14.12

Percona is glad to announce the release of Percona Server 5.1.73-14.12 on July 31st, 2014 (Downloads are available here and from the Percona Software Repositories). Based on MySQL 5.1.73, including all the bug fixes in it, Percona Server 5.1.73-14.12 is now the current stable release in the 5.1 series. All of Percona‘s software is …

About 1.5 months ago I blogged on MySQL 5.6 on POWER andtalked about what I had to poke at to make modern MySQL versions run and run well on shiny POWER8 systems.

One of those bugs, MySQL bug 47213 (InnoDB mutex/rw_lock should be conscious of memory ordering other than Intel) was recently marked as CLOSED by the Oracle MySQL team and the upcoming 5.6.20 and 5.7.5 releases should have the fix!

This is excellent news for those wanting to run MySQL on SMP systems that don’t have an Intel-like memory model (e.g. POWER and MIPS64).

This was the most major and invasive patch in the patchset for MySQL on POWER. It’s absolutely fantastic that this has made it into 5.6.20 and 5.7.5 and may mean that these new …

This article discusses the storage (inline and external) of field data in the InnoDB storage engine. All fields of variable length types like VARCHAR, VARBINARY, BLOB and TEXT can be stored inline within the clustered index record, or stored externally in separate BLOB pages outside of the index record (but within the same tablespace). All of these fields can be classified as large objects. These large objects are either binary large objects or character large objects. The binary large objects do not have an associated character set, whereas the character large objects do.

Within the InnoDB storage engine there is no difference between the way character large objects and binary large objects …

In WL#6045 we improved the innochecksum tool so that it opens the tablespace file and validates the checksum for each page. It compares the calculated checksum to the stored checksum in the page and reports mismatches, if any. It can also now rewrite page checksums in the tablespace. It is an offline tool, however, so make sure that the MySQL server is not using the tablespace files when running the innochecksum tool.

When InnoDB encounters a page checksum mismatch, it will cause an ASSERT and perform a forced shutdown. So rather than wait for InnoDB to encounter this in production, it is better to use the innochecksum tool to validate and correct any checksum issues ahead of time. You could perform these checks on your …

During last April’s Percona Live MySQL Conference and Expo, TokuDB celebrated it’s first full-year as an open source storage engine. I still remember reading the official announcement and the expectations it created one year ago. The premises were very interesting as it had the potential of helping MySQL manage “big data” in a way InnoDB just couldn’t. It also provided additional interesting features like “hot schema changes,” all the while making our dear flash storages last longer.

While I’ve kept an eye on the evolution of TokuDB this past year, I reckon I haven’t given it a try…. until recently, when a …

InnoDB has proven to be a reliable data storage engine for modern, high concurrency database systems. It is fully ACID compliant, and supports a wide range of isolation modes, from READ-UNCOMMITEED to SERIALIZABLE.

InnoDB multiversion concurrency control (MVCC) enables records and tables to be updated without the overhead associated with row-level locking mechanisms. The MVCC implementation in InnoDB largely eliminates the need to lock tables or rows during updates, and enables good performance for high concurrency workloads.

To learn more about this subject and related performance tuning topics tuning, take the MySQL Performance Tuning training course. This 4-day, instructor-led course is available as:

…

ibdconnect is a tool to connect an ibd file to a foreign ibdata file. it’s important to understand how it works as secondary keys may cause interesting behavior.

Here is a table with a unique secondary key:

CREATE TABLE `t1` (
`id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
`value` varchar(255) COLLATE utf8_unicode_ci NOT NULL,
PRIMARY KEY (`id`),
UNIQUE KEY `uni_value` (`value`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;

When I update InnoDB dictionary with ibdconnect it all goes well:

# ./ibdconnect -f  t1.idb -o  /var/lib/mysql/ibdata1 -d test -t t1

…

Updating test/t1 (table_id 13) with id 0xA3060000
SYS_TABLES is updated successfully
…

SYS_INDEXES is updated successfully
ibdconnect modifies content of ibdata1, so checksums are wrong now. innochecksum_changer from …

One interesting feature of MySQL, is that it supports a very large number of integer data types. From the MySQL manual:

The recent WebScaleSQL announcement has made quite a splash in the MySQL community over the last few weeks, and with a good reason. The collaboration between the major MySQL-at-scale users to develop a single code branch that addresses the needs of, well, web scale, is going to benefit the whole community. But I feel that the majority of community opinions and comments to date have been based on the announcement itself and the organizational matters only. What we have been missing is an actual look at the code. What actual new features and bug-fixes are there? Let’s take a look.

At the same time, as Percona is also a developer of an enhanced MySQL replacement database server, it’s natural to …