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Category: MySQL Data Recovery

Data loss after MySQL restart

Not so long ago I had a customer who experienced data loss after MySQL restart. It was really puzzling. MySQL was up & running for many months, but after the customer restarted MySQL server all tables have gone. The tables were still visible in SHOW TABLES output, but they were not readable:

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Recover corrupted or crashed MySQL database online

Earlier before we blogged about ways to recover corrupt MySQL database with TwinDB Data Recovery Toolkit. However learning curve of the toolkit is rather steep. It takes time to get familiar with InnoDB internals and the tool. And let’s be honest nobody gets prepared for data loss – people who prepare for disaster recovery take […]

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How to recover table structure from FRM files online

Recently we announced MySQL Data Recovery Portal. Here we automated some data recovery routines and published web interface to them. First, it was a tool to estimate recovery chances from corrupted InnoDB tablespaces. Now it’s even more exciting and useful feature – recovery table structure from FRM files online. There are several methods to recover MySQL table […]

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How to evaluate if MySQL table can be recovered

What are odds MySQL table can be recovered? This is the most asked question. Every single customer asks if their MySQL table can be recovered. Although it’s not possible to answer that with 100% confidence there are ways to estimate recovery chances. I will describe few tricks. Generally speaking, if data is on media there […]

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How to handle wrong page type in external pages

First step of successful MySQL data recovery is to find InnoDB pages with your data. Let’s call it first, because prerequisite steps are already done. InnoDB page type is a two bytes integer stored in the header of a page. For MySQL data recovery two are important: FIL_PAGE_INDEX. Pages of this type are nodes of […]

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Presenting TwinDB Data Recovery Toolkit on #SFMySQL Meetup

On 5 November, I’ll be speaking at #SFMySQL Meetup about Data Recovery Software for MySQL Add Slipped & DROP’d your TABLE? Recover w/TwinDB’s Undrop for InnoDB toolkit to your calendar. There will be a demo and if you want to try to undrop a table yourself bring in a laptop with Linux. Download the latest […]

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Resolving page corruption in compressed InnoDB tables

Sometimes corruption is not the true corruption. Corruption in compressed InnoDB tables may be a false positive. Compressed InnoDB table may hit false checksum verification failure. The bug (http://bugs.mysql.com/bug.php?id=73689) reveals itself in the error log as follows:

InnoDB complains that a stored checksum is zero. If you look closely it’s suspicious that calculated checksum […]

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Resolving ERROR 1050 42S01 at line 1 Table already exists

When ALTER TABLE crashes MySQL server it leaves orphaned records in InnoDB dictionary. It is annoying because next time you run the same ALTER TABLE query it will fail with error:

The post explains why it happens and how to fix it. When you run ALTER table InnoDB follows the plan: Block the original […]

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