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Fun with Bugs #53 - On Some Percona Software Bugs I've Reported

So far in this series I had written only/mostly about MySQL server bugs. Does it mean that there are no unique or interesting bugs in other MySQL-related software or MySQL forks and projects that use MySQL code?

Surely no, it doesn't. So, today I'd like to present a short list of currently active (that is, new or probably not yet resolved) bugs that I had reported for Percona's software at Launchpad over the years I use it. The list is based on this link, but I excluded minor reports and those that probably are just forgotten, while the problem is fixed long time ago.

Let me start with bugs in XtraBackup, the tool that plays a key role in most MySQL environments that are not using Oracle's Enterprise …

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MySQL Support Engineer's Chronicles, Issue #7

This week in Support was busy enough for me. Among other things I had to study all possible reasons (other than obvious query cache impact) for queries hanging in "query end" status and noted Bug #80652 related to binlog group commit and fixed in MySQL 5.7.17+ and 8.0.1+ only. The case I had to review was related to Galera though, and I suggest you to note that "query end" may be related to Galera replication stall. Studying this path further soon brought lp:1197771 - "Cluster stalls while distributing transaction" to my attention again, so I asked about proper status for it on Facebook. As it happens way too often recently, I've got few 'Likes" but no further comments, neither …

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MySQL Support Engineer's Chronicles, Issue #6

Previous post in series was published almost 4 months ago, but I do not plan to end it. So, let me quickly discuss some of problems I worked on or was interested in so far in June, and provide some useful links.

Back on June 2 I had to find out what exact files are created by MariaDB's ColumnStore when I create a table in this storage engine. Actually in recent versions one can check the tables in the INFORMATION_SCHEMA, but if still wonders why are all these directories with numbers in the names (/usr/local/mariadb/columnstore/data1/000.dir/000.dir/011.dir/193.dir/000.dir/FILE000.cdf), please, check also this …

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How to break MySQL InnoDB cluster

A few weeks ago I started experimenting with MySQL InnoDB cluster. As part of the testing, I tried to kill a node to see what happens to the cluster.

The good news is that the cluster is resilient. When the primary node goes missing, the cluster replaces it immediately, and operations continue. This is one of the features of an High Availability system, but this feature alone does not define the usefulness or the robustness of the system. In one of my previous jobs, I worked at testing a commercial HA system and I've learned a few things about what makes a reliable system.

Armed with this knowledge, I did some more experiments with InnoDB Cluster. The attempt from my previous article had no other expectation than seeing operations continue with ease (primary node …

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Fun with Bugs #51 - My Bug Reports that Oracle doesn't Want to Fix

This week I noticed (yet another) customer issue related to the output produced by mysqladmin debug command (or when mysqld process gets SIGHUP signal). I mean the output generated by the mysql_print_status() function. In this issue the content of the output was misinterpreted. I've seen this in the past more than once, and requested to document the output properly, but it never happened for a reason that there is an internal feature request to put this information elsewhere, in Performance Schema or Information Schema. The bug ended up with "Won't fix" status.

Surely I complained in a comment and on Facebook, and then …

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Fun with Bugs #50 - On Bugs Tagged as "missing manual"

Back in January 2014, some time after many nice people kindly asked me to shut up stop writing about MySQL bugs on Facebook several times per day, I decided to start reading the fine MySQL Manual more carefully than before and report not only typos there, but also any topic or detail not properly explained. Usually these reports, tagged as "missing manual", were the result of careful study of the documentation based on real user question or customer issue. So, most of these reports came from real life, and missing information badly affected poor MySQL users.

Today, for this issue #50 in my series of posts about MySQL bugs, I decided to list and …

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Fun with Bugs #49 - Applying PMP to MySQL

As you maybe noted, in several recent posts I've provided some additional details for slides used during my FOSDEM talk on profiling MySQL. The only part not covered yet is related to using Poor Man's Profiler (and pt-pmp version of it). I see no reason to explain what it does and how to use it once again, but would like to show several recent enough MySQL bug reports where this tool was essential to find, explain or demonstrate the problem.

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MySQL Support Engineer's Chronicles, Issue #5

A lot of time passed since my previous post in this series. I was busy with work, participating in FOSDEM, blogging about profilers and sharing various lists of MySQL bugs. But I do not plan to stop writing about my usual weeks of doing support engineer's job. So, time for the next post in this series, based on my random notes taken during the week here and there.

This week started for me with checking recent MySQL bug reports (actually I do it every day). …

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Fun with Bugs #48 - Group Replication Bugs and Missing Features as of MySQL 5.7.17

It seems recent post on Group Replication by Vadim caused an interesting discussion on Facebook. I am NOT going to continue it here, but decided to present some facts, specifically, list of public bug reports and feature requests for Group Replication (mostly "Verified", that is, accepted by Oracle engineers as valid) as of MySQL 5.7.17 (where the feature is promoted as GA), with just few comments to some of the bugs.

The goal is to double check this post when next Oracle MySQL 5.7.x release appears, to find out how much Oracle carews to fix the problems already identified by MySQL Community.

So, here are the bugs and feature requests in …

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MySQL super_read_only Bugs

This blog we describe an issue with MySQL 5.7’s super_read_only feature when used alongside with GTID in chained slave instances.

Background

In MySQL 5.7.5 and onward introduced the gtid_executed table in the MySQL database to store every GTID. This allows slave instances to use the GTID feature regardless whether the binlog option is set or not. Here is an example of the rows in the gtid_executed table:

mysql> SELECT * FROM mysql.gtid_executed;
+--------------------------------------+----------------+--------------+
| source_uuid                          | interval_start | interval_end | …
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