Shinguz's blog

Recently I switched on the MariaDB slow query logging flag log_queries_not_using_indexes just for curiosity on one of our customers systems:

We have sometimes discussions with our customers whether to store LOBs (Large Objects) in the database or not. To not rephrase the arguments again and again I have summarized them in the following lines.

The following items are more or less valid for all large data types (BLOB, TEXT and theoretically also for JSON and GIS columns) stored in a MySQL or MariaDB (or any other relational) database.

Preparing the MySQL Enterprise Administrator Training I found that the MySQL Enterprise Backup Incremental Backup is not described very well. Thus I tried it out and wrote down this how-to:

Differential Incremental Backup

The PAM authentication plugin is an extension included in MySQL Enterprise Edition (since 5.5) and in MariaDB (since 5.2).

When we do Galera Cluster consulting we always discuss with the customer if his software is Galera Cluster ready. This basically means: Can the software cope with the Galera Cluster specifics?

If it is a software product developed outside of the company we recommend to ask the software vendor if the software supports Galera Cluster or not.

We typically see 3 different answers:

From time to time we see in customer engagements that MySQL Master/Slave replication is set-up doing schema or table level replication filtering. This can be done either on Master or on Slave. If filtering is done on the Master (by the binlog_{do|ignore}_db settings), the binary log becomes incomplete and cannot be used for a proper Point-in-Time-Recovery. Therefore FromDual recommends AGAINST this approach.

MySQL is well known and widely spread because of its philosophy of Keep it Simple (KISS).

We recently had the discussion that with newer releases also MySQL and MariaDB relational databases becomes more and more complicated.

As you probably know MySQL is an Open Source product licensed under the GPL v2. The GPL grants you the right to not just read and understand the code of the product but also to use, modify AND redistribute the code as long as you follow the GPL rules.

In our current project the customer wants to install and run multiple MySQL Enterprise Server 5.7 Instances on the same machine (yes, I know about virtualization (we run on kvm), containers, Docker, etc.). He wants to use Redhat Enterprise Linux (RHEL) 7 which brings the additional challenge of SystemD. So mysqld_multi is NOT an option any more.

The MySQL Server itself

The differences between the MySQL Community Server and the MySQL Enterprise Server 5.7 are as follows as claimed by Oracle:

Prepare the RPM repository server

Install the software to create a RPM repository server (on an Ubuntu web server):

shell> sudo apt-get install createrepo

Create the directory structures and initialize the repositories:

shell> sudo mkdir -p /var/www/html/repos/centos/7/os/x86_64
shell> sudo createrepo /var/www/html/repos/centos/7/os/x86_64/

Copy the MySQL Enterprise RPM packages to the repository:

If you have already Red Hat Enterprise Linux 7 (RHEL 7) or CentOS 7 in use you probably found out, that it is not that easy to install MySQL Enterprise Server because there are already pre-installed MariaDB 5.5 libraries:

Today we had a very interesting phenomena at a customer. He complained that MySQL always get some errors of the following type:

[ERROR] mysqld: Sort aborted: Error writing file '/tmp/MYGbBrpA' (Errcode: 28 - No space left on device)

After a first investigation we found that df -h /tmp shows from time to time a full disk but we could not see any file with ls -la /tmp/MY*.

After some more investigation we found even the query from the Slow Query Log which was producing the same problem. It looked similar to this query:

FromDual has the pleasure to announce the release of the new version 0.10.6 of its popular Database Performance Monitor for MySQL, MariaDB, Galera Cluster and Percona Server fpmmm.

You can download fpmmm from here.

In the inconceivable case that you find a bug in fpmmm please report it to our Bug-tracker.

FromDual has the pleasure to announce the release of the new version 1.3.1 of its popular MySQL, Galera Cluster, MariaDB and Percona Server multi-instance environment MyEnv.

The new MyEnv can be downloaded here.

In the inconceivable case that you find a bug in the MyEnv please report it to our bug tracker.

When analysing MySQL configuration and status information at customers it is always interesting to see how the applications behave. This can partially be seen by the output of the SHOW GLOBAL STATUS command.

This week I was preparing the exercises for our MySQL/MariaDB for Beginners training. One of the exercises of the training is about MySQL spatial (GIS) features. I always tell customers: "With these features you can answer questions like: Give me all points of interest around me!"

Now I wanted to try out how it really works and if it is that easy at all...

A customer reported last month that MySQL does a full table scan (FTS) if a query was filtered by a INT value on a VARCHAR column. First I told him that this is not true any more because MySQL has fixed this behaviour long time ago. He showed me that I was wrong:

MariaDB 10.2 has introduced some Window Functions for analytical queries.

See also: Window Functions, Window Functions, Window function and Rows and Range, Preceding and Following

To synchronize the data between the Galera Cluster and a new or re-entering Galera node Galera Cluster uses 2 different mechanisms:

• For full synchronization of data: Snapshot State Transfer (SST).
• For delta synchronization of data: Incremental State Transfer (IST).

The Incremental State Transfer (IST) is relevant when a node is already known to the Galera Cluster and just left the cluster short time ago. This typically happens in a maintenance window during a rolling cluster restart.

How many connections can be opened concurrently against my MySQL or MariaDB database can be configured and checked with the following command:

SHOW GLOBAL VARIABLES LIKE 'max_connections';
+-----------------+-------+
| Variable_name   | Value |
+-----------------+-------+
| max_connections | 505   |
+-----------------+-------+

If this limit was ever reached in the past can be checked with:

FromDual has the pleasure to announce the release of the new version 1.2.2 of the popular Backup and Recovery Manager for MySQL and MariaDB (fromdual_bman).

You can download the FromDual Backup and Recovery Manager from here.

A MySQL customer of FromDual has different manufacturing plants spread across the globe. They are operated by local companies. FromDuals customer wants to maintain the manufacturing receipts centralized in a MySQL database in the Head Quarter in Europe. Each manufacturing plant should only see their specific data.

Manufacturing log information should be reported backup to European Head Quarter MySQL database.

We typically suggest our customers to use our MySQL/Galera Cluster my.cnf configuration template to avoid MySQL configuration and performance problems.

And we are paranoid as well. Thus we enable all useful logging:

wsrep_log_conflicts = 1

But this has also some consequences of more visibility...

From time to time we see at Galera Cluster customer engagements the following, for me scary, warning in the MySQL error log:

[Warning] WSREP: last inactive check more than PT1.5S ago (PT7.06159S), skipping check

We mostly see this in VMware set-ups. Some further enquiry with the Galera developers did not give a satisfying answer: