A few days ago, I stepped into a trap ! This made me lose time for fixing things (and even more for writing this post...). In the hope that you will avoid my mistake, I am sharing this war story. I also obviously opened a bug, more about this below.
TL&DR: be careful when using CHANGE MASTER TO MASTER_DELAY = N: it might wipe your relay logs !
As written in the TL&DR, running CHANGE MASTER
I've updated the bug tide graph I made in 2016 with today's data. The source code and details are here.
Lately, I worked on several queries which started returning wrong results after upgrading MySQL Server to version 5.7 The reason for the failure was derived merge optimization which is one of the default
optimizer_switch
options. Issues were solved, though at the price of performance, when we turned it
OFF
. But, more importantly, we could not predict if any other query would start returning incorrect data, to allow us to fix the application before it was too late. Therefore I tried to find reasons why
derived_merge
can fail. Analyzing the problem
In the first run, we turned SQL Mode
ONLY_FULL_GROUP_BY
on, and this removed most of the problematic queries. That said, few of the queries that were successfully working with
ONLY_FULL_GROUP_BY
were affected.
A quick search in the …
[Read more]What does Anton Ego – a fictional restaurant critic from the Pixar movie Ratatouille – have to do with MySQL 8.0 GA?
When it comes to being a software critic, a lot.
In many ways, the work of a software critic is easy. We risk very little and thrive on negative criticism, which is fun to read and write.
But what about those who give their many hours of code development, and those who have tested such code before release? How about the many people behind the scenes who brought together packaging, documentation, multiple hours of design, marketing, online resources and more?
And all of that, I might add, is open source! Free for the world to take, copy, adapt and even incorporate in full or in part into their own open development.
It is in exactly that area that the …
[Read more]When maintainng any piece of software, we usually deal with two kind of actions:
bugs and features
A bug happens when there is an error in the software, which does not behave according to the documentation or the specifications. In short, it's a breech of contract between the software maintainer and the users. The promise, i.e. the software API that was published at every major version, is broken, and the software must be reconciled with the expectations and fixed, so that it behaves again as the documentation says. When we fix a bug in this way, we increment the revision number of the software version …
[Read more]I am now in an airport, waiting for one of the four flights that will bring me to Percona Live Santa Clara 2018. This is a good time to write some details about my tutorial on parallel replication. But before talking about Percona Live, I will share thoughts on MySQL/MariaDB bugs that caught my attention in the last weeks/months (Valeriy: you clearly have an influence on me).
MySQL/MariaDB
We’re completing our move of Percona bug tracking into JIRA, and the drop-dead date is December 28, 2017.
For some time now, Percona has maintained both the legacy Launchpad bug tracking system and a JIRA bug tracking system for some of the newer products. The time has come to consolidate everything into the JIRA bug tracking system.
Assuming everything goes according to schedule, on December 28, 2017, we will copy all bug reports in Launchpad into the appropriate JIRA projects (with the appropriate issue state). The new JIRA issue will link to the original Launchpad issue, and the new JIRA issue link is added to the original Launchpad issue. Once this is done, we will then turn off editing on the Launchpad projects.
Q&A Which Launchpad projects are affected?
In my previous article about roles I said that one of the problems with role usage is that roles need to be activated before they kick in. Let's recap briefly what the problem is:
## new session, as user `root`
mysql [localhost] {root} ((none)) > create role viewer;
Query OK, 0 rows affected (0.01 sec)
mysql [localhost] {root} ((none)) > grant select on *.* to viewer;
Query OK, 0 rows affected (0.01 sec)
mysql [localhost] {root} ((none)) > create user see_it_all identified by 'msandbox';
Query OK, 0 rows affected (0.01 sec)
mysql [localhost] {root} ((none)) > grant viewer to see_it_all;
Query OK, 0 rows affected (0.01 sec)
## NEW session, as user `see_it_all`
mysql [localhost] {see_it_all} ((none)) > use test
ERROR 1044 (42000): Access denied for user 'see_it_all'@'%' to database 'test'
mysql [localhost] {see_it_all} ((none)) > show grants\G …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 …
[Read more]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 | …[Read more]
