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Showing entries 1 to 10 of 13 3 Older Entries

Displaying posts with tag: corruption (reset)

Resolving page corruption in compressed InnoDB tables
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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:

2014-10-18 08:26:31 7fb114254700 InnoDB: Compressed page type (17855); stored checksum in field1 0; calculated checksums for field1: crc32 4289414559, innodb 0, none 3735928559; page LSN 24332465308430; page number (if stored to page already) 60727; space id (if stored to page already) 448
InnoDB: Page …
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MySQL 5.5.40 Overview and Highlights
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MySQL 5.5.40 was recently released (it is the latest MySQL 5.5, is GA), and is available for download here:

http://dev.mysql.com/downloads/mysql/5.5.html

This release, similar to the last 5.5 release, is mostly uneventful.

There were 0 “Functionality Added or Changed” bugs this time, and 18 bugs overall fixed.

Out of the 18 bugs, most seemed rather minor or obscure, but there are 3 I think are worth noting (all 3 are InnoDB-related, regressions, and serious if you encounter them, so best to be aware of them):

  • InnoDB: An …
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Take image from corrupted hard drive
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There are at least two cases when it makes sense to take an image from a corrupted hard drive as soon as possible: disk hardware errors and corrupted filesystem. Faulty hard drives can give just one chance to read a block, so there is no time for experiments. The similar picture with corrupted filesystems. Obviously something went wrong, it’s hard to predict how the operating system will behave next second and whether it will cause even more damage.

Save disk image to local storage

Probably the best and fastest way is to plug the faulty disk into a healthy server and save the disk image locally:

# dd if=/dev/sdb …
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Recover Corrupt MySQL Database
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The unDROP for InnoDB tool can 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.

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Be careful if you use file-level symbolic links and myisamchk
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I ran into a rather obscure bug the other day, but while uncommon, it can cause damage you would not otherwise expect if you use file-level symbolic links. So this is just a warning about that.

Specifically, if you create a table with the .MYI and .MYD files in a different directory, using symbolic links – either manually or using CREATE TABLE .. INDEX DIRECTORY=”" DATA DIRECTORY=”", and then run myisamchk on the table and specify .MYI, you will corrupt the table.

Creating these manually is not so common, but the CREATE TABLE .. INDEX DIRECTORY=”" DATA DIRECTORY=”" is much more common, which creates file-level symbolic links (for the .MYI and .MYD files, …

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RAM flakier than expected
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Ref: Google: Computer memory flakier than expected (CNET DeepTech, Stephen Shankland)

Summary: According to tests at Google, it appears that today’s RAM modules have several thousand errors a year, which would be correctable if it weren’t for the fact that most of us aren’t using ECC RAM.

Previous research, such as some data from a 300-computer cluster, showed that memory modules had correctable error rates of 200 to 5,000 failures per billion hours of operation. Google, though, found the rate much higher: 25,000 to 75,000 failures per billion hours.

This …

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On Ma.gnolia, and data recovery
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There’s a good podcast from Chris Messina and Larry Halff, about what really happened at Ma.gnolia. If you’re at all interested in what happened (i.e. how did they lose all their bookmark data), don’t hesitate to watch the video. I took some quick notes:

  • half a terabyte database file got corrupted
  • a mysql 5 database
  • everything was running even though there was corruption, and eventually, the site went down
  • backup system also failed, as it didn’t backup the data …
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Replication Checksumming Through Encryption
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Problem

A problem we occasionally see is Relay Log corruption, which is most frequently caused by network errors. At this point in time, the replication IO thread does not perform checksumming on incoming data (currently scheduled for MySQL 6.x). In the mean time, we have a relatively easy workaround: encrypt the replication connection. Because of the nature of encrypted connections, they have to checksum each packet.

Solution 1: Replication over SSH Tunnel

This is the easiest to setup. You simply need to do the following on the Slave:

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MySQL Data Woes... or, Making Use of the Information_Schema
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To be fair - I highly doubt it has anything to do with MySQL.Database corruption - that's a different issue, often related to a bug in database code; but this was a data corruption issue, which is always a pain in the you know what to figure out and get fixed.I spent the last day trying to figure out the weirdness in a couple of our databases, digging around, explaining to developers that

Relay binlog corrupt
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The slave failed with the error that the relay binlog is corrupt. It had copied close to 12 binlogs from the master and they were yet to be applied. Unfortunately those binlogs have been purged on the master. Now to sync up cleanly we might have to refresh data from the master which can be costly since it was a 290 GB database. We had the option of shutting down the server. We thought we can try our luck with a crazy hack. We shutdown the server. Tried reading the binlog using mysqlbinlog utility from the corrupt position. It failed as expected. Then we tried reading from the next immediate position and it went through fine. Now we had a proof that our hack might …

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Showing entries 1 to 10 of 13 3 Older Entries

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