Myisam on FromDual GmbH

Limiting MySQL tmpdir size

oli.sennhauser@fromdual.com (Oli Sennhauser) — Thu, 29 Apr 2021 17:37:22 +0000

Today a customer gave me the idea of using a separate file as a volume for limiting the MySQL tmpdir size. On some not so well set-up Linux systems the MySQL tmpdir is located under /tmp which is the same mount point as / (root). This can lead to troubles in case the tmpdir is filled up with implicit temporary MyISAM tables which fills up the / (root) directory of the O/S as well.

MyISAM locking and who is the evil?

oli.sennhauser@fromdual.com (Oli Sennhauser) — Wed, 23 Sep 2020 09:58:35 +0000

Yes, I know, MyISAM is deprecated and unofficially discontinued by the vendors. But we still have from time to time customers using MyISAM and even evangelize for MyISAM…

Flush time is set

oli.sennhauser@fromdual.com (Oli Sennhauser) — Wed, 15 Jul 2015 06:10:36 +0000

If the variable flush_time is set to a non-zero value, all tables are closed (and flushed) every flush_time seconds to disk. This can cause unnecessary and high I/O spikes.

Switching from MySQL/MyISAM to Galera Cluster

oli.sennhauser@fromdual.com (Oli Sennhauser) — Tue, 12 Mar 2013 08:23:36 +0000

Switching from MySQL/MyISAM to Galera Cluster requires that all tables (except those from the mysql, information_schema and performance_schema) are using the InnoDB Storage Engine.

MySQL tmpdir on RAM-disk

oli.sennhauser@fromdual.com (Oli Sennhauser) — Thu, 15 Nov 2012 19:15:49 +0000

MySQL temporary tables are created either in memory (as MEMORY tables) or on disk (as MyISAM tables). How many tables went to disk and how many tables went to memory you can find with:

Change MyISAM tables to InnoDB and handle SELECT COUNT(*) situation

oli.sennhauser@fromdual.com (Oli Sennhauser) — Tue, 12 Jun 2012 20:48:38 +0000

Its a known problem that changing the Storage Engine from MyISAM to InnoDB can cause some problems
[ 1
] if you have queries of this type:

How MySQL behaves with many schemata, tables and partitions

oli.sennhauser@fromdual.com (Oli Sennhauser) — Wed, 30 Nov 2011 15:35:28 +0000

Introduction

Recently a customer claimed that his queries were slow some times and sometimes they were fast.

How good is MySQL INSERT TRIGGER performance

oli.sennhauser@fromdual.com (Oli Sennhauser) — Wed, 03 Aug 2011 17:08:36 +0000

Abstract: In this article we discuss how big is the performance impact of MySQL TRIGGERs compared to application side logging (with INSERT) into a MySQL table.

How many warm MyISAM key blocks do you have?

oli.sennhauser@fromdual.com (Oli Sennhauser) — Mon, 18 Oct 2010 17:56:44 +0000

When you are working with MyISAM [ 1 ] tables MySQL provides a feature called the Midpoint Insertion Strategy [ 2 ]. You can enable it with the parameter key_cache_division_limit [ 3 ].

MySQL Questions & Answers

oli.sennhauser@fromdual.com (Oli Sennhauser) — Mon, 15 Mar 2010 11:15:25 +0000

Search with special characters

This Question has been moved to the Forum.

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.

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…