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Displaying posts with tag: crash (reset)
Fun with Bugs #39 - Known Bugs in MySQL 5.7.9 GA

These days everybody is excited with recent announcement of MySQL 5.7.9 GA release. If you are not aware of this event yet (I've noted it from numerous posts even during my short vacation), wait for the Oracle Open World 2015 to begin tomorrow to announce it even wider and louder!

I already have 5.7.9 built from source, up and running, so it's time to check what else we can expect from this new GA release besides new great features (this is a topic for a separate post or two) and usual excitement. Yes, I mean known, verified bugs in MySQL 5.7.9.

Let me start with a quick summary and then present the details. So, even though MySQL Community tried hard to check 5.7.x at early stages and report bugs to Oracle, MySQL 5.7.9 GA has a number of known …

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How to create a rock-solid MySQL database backup & recovery strategy

Have you ever wondered what could happen if your MySQL database goes down?

Although it’s evident such a crash will cause downtime – and surely some business impact in terms of revenue – can you do something to reduce this impact?

The simple answer is “yes” by doing regular backups (of course) but are you 100% sure that your current backup strategy will really come through when an outage occurs? And how much precious time will pass (and how much revenue will be lost) before you get your business back online?

I usually think of backups as the step after HA fails. Let’s say we’re in M<>M replication and something occurs that kills the db but the HA can’t save the day. Let’s pretend that the UPS fails and those servers are completely out. You can’t failover; you have to restore data. Backups are a key piece of “Business Continuity.” Also factor in the frequent need to restore data that’s been …

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MySQL 5.5.40 Overview and Highlights

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 ALTER TABLE … ADD FOREIGN KEY operation could cause a serious error. (Bug #19471516, Bug #73650)
  • InnoDB: With a transaction isolation level less than or equal to READ COMMITTED, gap locks …
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On responsible bugs reporting

Let me start with questions related to responsible MySQL bugs reporting that I'd like to be discussed and then present a history behind them.

Assuming that you, my dear reader from MySQL Community, noted or found some simple sequence of SQL statements that, when executed by authenticated MySQL user explicitly having all the privileges needed to execute these statements, crashes some version of your favorite MySQL fork, please, answer the following questions:

  1. Do you consider this kind of a bug a "security vulnerability"?
  2. Should you share complete test case at any public site (MySQL bugs database, Facebook, your personal blog, any)?
  3. Should you share just a description of possible "attack vector", as Oracle does when they publish security bug fixes?
  4. Should you share just a stack trace or failed assertion information, without any details on how to get it?
  5. Should …
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Are MariaDB tests adding anything extra over Oracle MySQL tests?

I grabbed all the tests introduced in MariaDB 5.5.32 (i.e. “bzr diff -rtag:mariadb-5.5.31..mariadb-5.5.32 mysql-test/” and some foo) and threw them in their own test file. I only kept tests for crashing bugs and ignored those that required plugins (there were two or three, but nothing major). So now I have a test file that should crash MariaDB 5.5.31 and probably before. But, the question is: does this crash Percona Server or MySQL?

While it is excellent to see the MariaDB guys including tests for their crashing bugs, are these MariaDB specific or do they affect other MySQL flavours?

I built a release build of top of trunk Percona Server and ran the test against it. I got no crashes. In a debug build, I got two. One was to do with REPAIR on an ARCHIVE table and the other was “SELECT UNIX_TIMESTAMP(STR_TO_DATE(’2020′,’%Y’));”. I found the same thing for a debug build of top of tree MySQL.

All the other tests …

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Initial Reactions to MySQL 5.6

New versions of MySQL are always interesting to try out. Often they have features which I may have asked for myself so it’s satisfying to see them eventually appear on a system I use. Often other new features make life easier for the DBA. Finally we hope overall performance will improve and managing the server(s) will be come easier.

So I had a system which needs to make heavy writes, and performance was a problem, even when writing to SSDs. Checkpointing seemed to be the big issue and the ib_logfile size in MySQL 5.5 is limited to 4 GB. That seems a lot, but once MySQL starts to fill these files (and this happens at ~70% of the total I believe),  checkpointing kicks in heavily, and slows things down.  So the main reason for trying out MySQL 5.6 was to see how things performed with larger ib_logfiles. (Yes, MariaDB 5.5 can do this too.)

Things improved a lot for my specific workload which was great news, but one thing …

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Nasty Regression Bug Seems Fixed in 5.5.18

For those who saw my previous post about the crashing (regression) bug with SELECT COUNT(DISTINCT) on InnoDB with Primary Key (PK), you’ll be interested to know my test case does not crash in 5.5.18 (which was just released).

I’ve only tested my test case thus far, but it seems fine.

Unfortunately, the fix is not mentioned in the 5.5.18 changelogs though.

And there is no mention (yet, anyway) of a fix in the bug report I filed (though it was designated a ‘duplicate’, so it wouldn’t necessarily be updated).

I’m trying to get confirmation from the MySQL Dev Team on this (via the bug report), and will update this post if/when I hear anything.

I’ll also perform some of the …

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Nasty Regression Bug: SELECT COUNT(DISTINCT) crashes InnoDB when WHERE operand is in Primary Key or Unique Index

In 5.5, a crashing, regression bug exists if you use SELECT COUNT(DISTINCT) *and* one of the WHERE operands is in the Primary Key (or just a unique index).

This simple crash (if only one row is in the table) will crash mysqld.

Of course I’ve filed a bug report, but that has been nearly 3 months and no updates yet.

Here is the bug I filed (which you won’t be able to view):

http://bugs.mysql.com/bug.php?id=61842

Really, the only thing that happened to my bug report was that it was designated a duplicate of another bug (which we also cannot view):

http://bugs.mysql.com/bug.php?id=61101

Based on the id, and the submitted dates of bugs 61100 and 61102, this initial bug (61101) was filed on May 9, 2011. So, in fact, this bug has been present for over …

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Unexpected mysqld crashing in 5.5

An update of MySQL from 5.0 to 5.5 on CentOS 5.5 64bit has not resulted in a good experience. The mysqld process would then crash every few minutes with the following message.

101120 8:29:27 InnoDB: Operating system error number 22 in a file operation.
InnoDB: Error number 22 means ‘Invalid argument’.
InnoDB: Some operating system error numbers are described at
InnoDB: http://dev.mysql.com/doc/refman/5.1/en/operating-system-error-codes.html
InnoDB: File name /tmpfs/#sql6cf3_5c_0.ibd
InnoDB: File operation call: ‘aio write’.
InnoDB: Cannot continue operation.

The work around was to change the tmpdir=/tmpfs (which was a 16G tmpfs filesystem) to a physical disk.

The referenced URL didn’t provide any more information of help. Unlike Bug #26662 O_DIRECT is not specified as the flush method.

A Quick Review of Stack Traces

I'll try to pass on some basic knowledge about those confusing stack traces we sometimes see in the mysql error logs.  What can you tell from them, what are they useful for, and how to validate them?
Debugging Crashes
We tried to improve postmortem debugging of crashes + stack traces in the error log:o) old versions of mysqld only printed numerical numbers instead of function names (if you're lucky!)o) some platforms/architectures printed no stack trace what-so-ever!o) …

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