Very often MySQL is much less stable than we realize. In this video I explain how to detect and dianose these MySQL stalls that last for 5-10 seconds or more.

The reason nobody knows about these issues is that they’re:
a) rare
b) intermittent
c) monitoring software can’t catch them

You can use pt-stalk to detect and diagnose such issues. All of the tools I have mentioned in this video are part of Percona Toolkit (no wonder they all start with PT), you can find the toolkit here:

Percona Toolkit

Here’s the main commands I have discussed in this video:

Starting pt-stalk in foreground

# pt-stalk

Starting pt-stalk in background with email notification:

# pt-stalk …

This release fixes a few issues in the new GUI transactions supporting with specific and uncommon server settings.

Changes as compared to SQLyog MySQL GUI 12.3.1 include:

Bug Fixes:

* If an INIT_CONNECT setting in server configuration specified SET AUTOCOMMIT = 0 and global AUTOCOMMIT was 1 (or non-existent as in MySQL 4.1 and 5.0), the ‘transactions’ menu in SQLyog would incorrectly display AUTOCOMMIT as 1 after connection.
* Same code change as above also fixes a crash that could occur with 4.1 servers.
* Transactions support would fail to initialize with servers running global ANSI mode. SQLyog will not work in ANSI mode but connection and initialization should work, so that user as the first step may specify a supported session sql_mode (from the editor or from ‘advanced’ tab in connection …

Join Percona’s Percona XtraDB Cluster Lead Software Engineer Krunal Bauskar for a webinar on Thursday, November 17, 2016, at 7:30 am PST on MySQL High Availability with Percona XtraDB Cluster 5.7.

Percona XtraDB Cluster 5.7 is our brand new MySQL 5.7 compatible Galera-based high availability (HA) solution. Whether you’re new to MySQL clustering technology, or experienced with Galera-based replication, this tutorial provides great insights into working with the software, …

Using Vault with MySQL

In my previous post I discussed using GPG to secure your database credentials. This relies on a local copy of your MySQL client config, but what if you want to keep the credentials stored safely along with other super secret information? Sure, GPG could still be used, but there must be an easier way to do this.

This post will look at a way to use Vault to store your credentials in a central location and use them to access your database. For those of you that have not yet come across Vault, it is a great way to manage your secrets – securing, storing and tightly controlling access. It has the added benefits of being able to handle leasing, key revocation, key rolling and auditing.

During this blog post we’ll accomplish the following …

This blog post looks at MongoDB and MySQL, and covers high-level MongoDB strengths, weaknesses, features, and uses from the perspective of an SQL user.

Delving into NoSQL coming from an exclusively SQL background can seem like a daunting task. I have worked with SQL in both small MySQL environments and large Oracle SQL environments. 

When is it a good choice?

MongoDB is an incredibly robust, scalable, and operator-friendly database solution. MongoDB is a good choice when your developers will also be responsible for the database environment. In small shops and startups, this might be the case. MongoDB stores information in BSON (binary JSON). BSON is the native JSON (JavaScript Object Notation) language used by MongoDB to retrieve information stored in BSON on the back end. JSON is easily relatable to other programming languages, and many developers will already have experience with it.

…

Some days ago we found very interesting bug report with my friend: http://bugs.mysql.com/bug.php?id=71879

Problem is that, if a client moves binlog files to the other folder, stops MySQL server, update in the config file bin_log and bin_log_index values for a new path and starts server again, then the result of SHOW BINARY LOG command will be wrong:

mysql> show binary logs;
+-------------------------+-----------+
| Log_name                | File_size |
+-------------------------+-----------+
| cluster-repo-bin.000001 |       120 |
| cluster-repo-bin.000002 |         0 |
| cluster-repo-bin.000003 |         0 |
| cluster-repo-bin.000004 |         0 |
| cluster-repo-bin.000005 |         0 |
| cluster-repo-bin.000006 |       120 |
+-------------------------+-----------+

As you see, the size of some binlog files are zero. So why?

If you …

According to this bug report http://bugs.mysql.com/bug.php?id=79151

when client tries to create a new table with not existing (or write permission denied) datadir, then he gets an error message like this: ERROR 1030 (HY000): Got error -1 from storage engine

As you see it is not informative error message, we don’t know what’s wrong at the backend. But in the version 5.7 it seems this problem was resolved already.

I discovered that at the low level of innodb storage engine, program tries to create subfolders, when occurs a problem it checks system error partly in the file storage/innobase/fil/fil0fil.cc:

success = os_file_create_subdirs_if_needed(path);

os_file_create_subdirs_if_needed function in the storage/innobase/os/os0file.cc file checks system errors but returns only boolean value depending on the …

My first bug fix was about a year ago. You can see bug report here: http://bugs.mysql.com/bug.php?id=72259

If to shortly explain, so problem was that when you make file system read only, and try to start the server, it fails. And there is no exact error message in the log files which explains the problem correctly.

I added to the sql/mysqld.cc file a simple function whitch checks the given path’s permission and returns the state code:

// checks if file system is read-only

int is_filesystem_read_only(char const* name) {

    if (access(name, W_OK) == -1) {

        if (access(name, R_OK) == 0) {

            return R_OK; // read only

        } else if (access(name, F_OK) == 0) {

      …

This blog post was motivated by an internal discussion about how to fully disable query cache in MySQL.

According to the manual, we should be able to disable “Query Cache” on the fly by changing

query_cache_type

 to 0, but as we will show this is not fully true. This blog will show you how to properly disable “query cache,” and how common practices might not be as good as we think.

Can we just disable it by changing variables, or does it requires a restart to avoid the global mutex? Let’s see how it works.

Some Query Cache context

The query cache stores the text of a “Select” statement together with the corresponding result that was sent to the client. If an identical statement is received later, the server retrieves the results …

This post discusses ways of fixing broken GTID replication.

This blog series is all about the daily stories we have in Managed Services, dealing with customers’ environments (mostly when we need to quickly restore a service level within the SLA time).

One of the issues we encounter daily is replication using the GTID protocol. While there are a lot of blogs written about this subject, I would like to just highlight GTID replication operations, and the way you can deal with broken replication.

Most of the time we face way more complex scenarios then the one I’m about to present as an example, but the main goal of this blog is to quickly highlight the tools that can be used to fix issues to resume replication.

After reading this blog, you might ask yourself “Now, we …