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Displaying posts with tag: regression (reset)

Fun with Bugs #28 - regression bugs in MySQL 5.6
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2013 was a great year for MySQL Community. New MySQL 5.6 GA release with its increased throughput, scalability and new features as well as more interaction and cooperation with MySQL Community from Oracle side brought us a lot of new perspectives and good feelings over the year.

Unfortunately new MySQL 5.6 GA release also reminded about old and well known problem with new MySQL versions. They all introduce new regression bugs. MySQL 5.6 had not become an exception.

Note that according to good old tradition (that I hope will be followed in 2014) bugs that demonstrate a regression (make some feature that previously worked stop functioning as intended in a new release) are marked with "regression" tag at http://bugs.mysql.com.



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Fun with Bugs #22 - Some Bug Reports You Should Not Miss
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Yet another user installed MySQL 5.5.32 yesterday and got a system that can not start... It's really easy to help in this case - just downgrade back to 5.5.31 or upgrade to 5.5.33 if you can. Why problem happened during upgrade? Because of a regression bug #69623.

This case that was easily solved during a quick chat reminded me about the problem of bugs in production. Nobody expects any sane DBA to review every new bug report, but some of them should not be missed, at least when upgrading to any newer version. Regression bugs (I see 15

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Fun with Bugs #19 - waiting for MySQL 5.6.13 and some real fun?
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I feel like MySQL 5.6.12 was released ages ago, while in reality it was on June 3, less than 2 months ago. No wonder I feel so, after writing several posts about bugs fixed and not fixed in it... Anyway, we still have to wait for MySQL 5.6.13 for a week or even two probably and in the meantime I decided to write new post for this series based on good old idea of making a digest of my recent bugs-related posts at Facebook. I know, it's boring and annoying (same as waiting for the release of 5.6.13).

Let's start with Bug #69846 - "ICP does not work on UNIQUE indexes". Based on my quick tests presented there I'd say that ICP (

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Fun with Bugs #15 - Recent News and Hawthorne Effect Studies
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Let me present a quick review of new and recently verified MySQL bug reports (mostly in 5.6.12, but not only). Surely I have to start with this request that many my colleagues had already mentioned in their blogs:

Bug #69558 - Put *all* know bugs into the public bug tracking system at bugs.mysql.com. We may argue on how and when this should apply to "security" bugs, but automatic bi-directional replication (even if delayed) with Oracle internals bugs database is what I was also asking for since we were forced to use it. Click on "Affects Me" button there and let's hope that some day Oracle will publish list of bugs that affect most of community users and may even try to take this into account while making decisions.

I have good news for everybody who was following MySQL 5.6



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Fun with Bugs #14 - InnoDB in MySQL 5.6
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InnoDB improvements in MySQL 5.6 are well known. One of the key reasons to upgrade to MySQL 5.6 for most users is to get the benefits of improved performance, scalability, new monitoring features and fulltext indexes support in InnoDB.

Is there anything to double check before assuming that InnoDB in MySQL 5.6 is just better than any older version for any practical purposes? Let's review known public InnoDB-specific bug reports. Here is my "Top 10" list, as of MySQL 5.6.12, starting with most recent reports:

  • Bug #69424  - maybe I miss something (I am not the only one though), but I see no way to continue using raw devices (on Linux at least) to store InnoDB data. You had working raw device in 5.5.32, then you upgrade to 5.6.12 and just can not start MySQL any more.




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    Fun with Bugs #11 - Top 10 Optimizer Regression Bugs in MySQL 5.6
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    I've got a question from colleague last night on what bugs should users take into account if they plan to upgrade to MySQL 5.6 now. Simple answer is: it depends. If one of the new features or scalability improvements are really important, then bugs in other features or clearly identified problematic use cases may be just ignored or avoided.

    But to be on a safe side users should at least check if they are (or may be) affected by a known regression bugs, when new version is slower or produce wrong results or crashes in cases that worked without problems before.

    List of bugs in MySQL 5.6 that can be formally considered as regressions comparing to previous major versions would be long enough for a single post. So I'd like to concentrate on regression bugs in Optimizer here:





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    Serious XFS Performance Regression in Linux Kernel 2.6.32-279
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    I'm not the only one to have noticed this, but I spent a sufficient amount of time banging my head against a wall finding this out that I thought it important to make more people aware of this.

    While trying to validate new database hardware we were seeing some serious performance issues in production.  Most MySQL benchmarks using sysbench or pt-playback couldn't reproduce it, but a simple sysbench 16 threaded filio test on the mysql partition showed about 1/3 the throughput we would expect.   The fact that much of the hardware was new as well as the OS we were using made tracking down the cause difficult (changing from CentOS 5.5 to Scientific Linux 6.)

    Finally some of our ops people working on different systems started noticing similar issues, and they uncovered the XFS issue.  Sure enough -- when took existing hardware,



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    Nasty InnoDB regression in MySQL 5.5.25
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    We just ran into a nasty InnoDB bug that only seems to exist in MySQL 5.5.25:

    An InnoDB update that modifies a rows primary key can trigger some recursive behavior that creates new rows until all disk space is exceeded. This does not affect all primary key updates in general but only gets triggered when a few other conditions are also met, so you're not too likely to run into it, but if you do your mysqld server will waste a lot of IO bandwidth and storage space on this and will usually eventually run out of disk space.

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    Nasty Regression Bug Seems Fixed in 5.5.18
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    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

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    Nasty Regression Bug: SELECT COUNT(DISTINCT) crashes InnoDB when WHERE operand is in Primary Key or Unique Index
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    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 5

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    Showing entries 1 to 10 of 12 2 Older Entries

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