The FromDual Blogs on FromDual GmbH

What is the quickest way to load data into the database?

oli.sennhauser@fromdual.com (Oli Sennhauser) — Wed, 11 Feb 2026 10:04:00 +0100

We had some really exciting problems to solve for the last customer! Especially because the database wasn’t exactly small.

How much space does NULL need?

oli.sennhauser@fromdual.com (Oli Sennhauser) — Sun, 08 Feb 2026 16:15:00 +0100

The last time I consulted a customer, he came up to me beaming with joy and said that he had taken my advice and changed all the primary key columns from BIGINT (8 bytes) to INT (4 bytes) and that had made a big difference! His MySQL 8.4 database is now 750 Gbyte smaller (from 5.5 Tbyte). Nice!

Someone is deleting my shared memory segments!

oli.sennhauser@fromdual.com (Oli Sennhauser) — Sun, 08 Feb 2026 06:27:00 +0100

When we work with PostgreSQL under our myEnv, we regularly get shared memory segment errors. Example:

Load CSV files into the database

oli.sennhauser@fromdual.com (Oli Sennhauser) — Fri, 06 Feb 2026 18:04:00 +0100

Recently, I wanted to display the places of residence of the members of my club on a map for a personal gimmick (IGOC members). I knew the addresses of the club members. But not the coordinates of their places of residence.

We build a data warehouse from the General Query Log

oli.sennhauser@fromdual.com (Oli Sennhauser) — Wed, 31 Jan 2024 16:41:13 +0100

The design of a data warehouse differs from relational design. Data warehouses are often designed according to the concept of the star schema.

Linux Container with Incus for focmm unit testing

oli.sennhauser@fromdual.com (Oli Sennhauser) — Thu, 13 Oct 2022 19:11:40 +0200

Currently we are in the testing phase of the next release of our Ops Center (focmm). This testing is quite complex because it includes testing the interaction of various different components like a MariaDB Galera Cluster, a Galera Load Balancer, a virtual IP, etc.

Data Warehouse Design

oli.sennhauser@fromdual.com (Oli Sennhauser) — Wed, 16 Jun 2021 23:02:43 +0200

This is my cheat sheet for dimensional modelling design techniques of a data warehouse (DWH) according to Kimball/Ross.

Query performance comparison between MariaDB ColumnStore and other Storage Engines

oli.sennhauser@fromdual.com (Oli Sennhauser) — Thu, 03 Jun 2021 15:53:51 +0200

Storage Engines like InnoDB, Aria and MyISAM are Row Stores. They store rows one after the other in blocks or even directly in a single file (MyISAM). On the other hand a Column Store like MariaDB ColumnStore stores all the same attributes (columns) of the rows together in chunks.

Create a single-node MariaDB ColumnStore test installation

oli.sennhauser@fromdual.com (Oli Sennhauser) — Wed, 19 May 2021 19:37:50 +0200

For a long time I wanted to investigate a bit more into the MariaDB ColumnStore architecture. Now I took the time to start with.

Do not trust other peoples benchmarks!

oli.sennhauser@fromdual.com (Oli Sennhauser) — Tue, 06 Apr 2021 13:26:06 +0200

Because they do NOT reflect your problems.

One of our customers upgraded last month from MariaDB 10.2 to MariaDB 10.5. In the same change he also converted all his data warehouse (DWH)/BI tables from MyISAM to Aria. An all this, naturally, without testing. And it miserably failed! And then we were under heavy time pressure to make things working again…

MySQL Binary Log Filter does not work

oli.sennhauser@fromdual.com (Oli Sennhauser) — Wed, 21 Oct 2015 05:23:36 +0200

Problem

We use the following binary log filter for filtering out some schemata.

MySQL Replication Slave is lagging more and more

oli.sennhauser@fromdual.com (Oli Sennhauser) — Fri, 18 Sep 2015 05:36:36 +0200

Problem

My MySQL Replication Slave is lagging more and more and I have no clue why. This happens since last weekends application change. I see that one Core is running at 100% user time but the I/O system is nearly completely idle. Any help is appreciated!

MySQL Replication Slave with corrupt Relay Logs

oli.sennhauser@fromdual.com (Oli Sennhauser) — Thu, 16 Jul 2015 19:19:36 +0200

Problem

MySQL Replication Slave stuck because its disk run full. After restarting the Slave MySQL replication was broken with the following error:

Support policy for MariaDB, MySQL and PostgreSQL

oli.sennhauser@fromdual.com (Oli Sennhauser) — Tue, 23 Dec 2014 15:46:54 +0100

Distribution maintenance policies
MariaDB Lifetime Support Matrix for MariaDB Releases
MariaDB Corp Enterprise Support Subscriptions
MySQL Lifetime Support Matrix for MySQL Releases
Oracle Corp Enterprise Support Subscriptions for MySQL
PostgreSQL Versioning Policy
Database Support by FromDual

Distribution maintenance policies

Maintenance policies for Long Term Support (LTS) releases of common distributions:

MariaDB and MySQL PERFORMANCE_SCHEMA Hints

oli.sennhauser@fromdual.com (Oli Sennhauser) — Sun, 14 Jul 2013 09:29:09 +0200

Accounts not properly closing connections
Unused indexes
Who created temporary (disk) tables
Accounts which never connected since last start-up
Users which never connected since last start-up
Totally unused accounts (never connected since last restart and not used to check Stored Program or View privileges) since last start-up
SHOW FULL PROCESSLIST
Storage Engines per schema
Tables without a Primary Key
Bad SQL queries of users
SHOW PROFILE in PERFORMANCE_SCHEMA
SELECT, INSERT, UPDATE and DELETE per table
Top long running queries
Tables never written to
DML, DDL and DCL per account
Finding syntactically wrong/erroneous MySQL queries
Finding queries served by MySQL Query Cache
Grant access to sys schema to another user
Grant access to PERFORMANCE_SCHEMA schema to another user
Find InnoDB Locks
Find Metadata Locks
What did a Connection before sleeping?
How many statements did another (sleeping) connection?
MyISAM locking
Connections per user
Connections per user and IP
Accounts which could not connect or with connection errors
Temporary tables filling my disk
Who is writing to the binary log
Average binlog transaction size
Result size of SELECT statement
Find open long running transactions

MariaDB

On MariaDB you have to enable the Performance Schema first before use:

Be careful when using SAN

oli.sennhauser@fromdual.com (Oli Sennhauser) — Sun, 06 Mar 2011 10:13:39 +0000

Be careful when using SAN (Storage Area Networks) or similar shared storage solutions (and any other virtualization, consolidation or cloud solutions).

The battle against Oracle is probably over but has the real war begun yet?

oli.sennhauser@fromdual.com (Oli Sennhauser) — Wed, 20 Jan 2010 09:36:00 +0100

According to different sources from the web the decision about the Oracle - Sun merger has been approved by the European commission soon. So at least in the West it is clear what is going on. Let us see what the East decides… [ 1 ], [ 2 ].

The FromDual Blogs on FromDual GmbH

What is the quickest way to load data into the database?

How much space does NULL need?

Someone is deleting my shared memory segments!

Load CSV files into the database

We build a data warehouse from the General Query Log

Linux Container with Incus for focmm unit testing

Data Warehouse Design

Query performance comparison between MariaDB ColumnStore and other Storage Engines

Create a single-node MariaDB ColumnStore test installation

Table of Contents

Do not trust other peoples benchmarks!

MySQL Binary Log Filter does not work

Problem

MySQL Replication Slave is lagging more and more

Problem

MySQL Replication Slave with corrupt Relay Logs

Problem

Support policy for MariaDB, MySQL and PostgreSQL

Table of Contents

Distribution maintenance policies

MariaDB and MySQL PERFORMANCE_SCHEMA Hints

Table of Contents

MariaDB

Be careful when using SAN

The battle against Oracle is probably over but has the real war begun yet?