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table_open_cache

Linux system calls of MySQL process

We had the problem today that a MySQL Galera Cluster node with the multi-tenancy pattern caused a lot of system time (sy 75%, load average about 30 (you really must read this article by Brendan Gregg, it is w

Table definition cache too small

The number of table definitions (from .frm files) that can be stored in the definition cache (table_definition_cache). If you use a large number of tables, you can create a large table definition cache to speed up opening of tables.
The command SELECT COUNT(*) FROM information_schema.tables; shows you roughly how many table definitions you have. Open_table_definitions is the current amount of open table definitions.

Table open cache too small

Table Open Cache (table_open_cache, old table_cache) is the number of open tables (Open_tables) for all threads. Increasing table_open_cache increases the number of file descriptors (open_files_limit) that MySQL requires.

Could not increase number of max_open_files

Hello all, on some Linux systems I get the following warning during my MySQL database start-up:
[Warning] Buffered warning: Could not increase number of max_open_files to more than 1024 (request: 8192)
[Warning] Buffered warning: Changed limits: max_connections: 214 (requested 505)
[Warning] Buffered warning: Changed limits: table_cache: 400 (requested 512)

What does it mean and is that something I should care about?

Troubles with MySQL 5.5 on FreeBSD 9

FreeBSD 9 seems to have some troubles with MySQL 5.5.20. A customer has moved from MySQL 5.0 on Linux to MySQL 5.5 on FreeBSD 9. He experienced a lot of periodic slow downs on the new, much stronger, system which he has not seen on the old Linux box.

This slow downs were also shown in high CPU system time but we could not see any I/O going on.

When we looked into MySQL we have seen many threads in Opening tables state in the MySQL processlist.

How MySQL behaves with many schemata, tables and partitions

Introduction

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

First idea: Flipping query execution plan caused by InnoDB could be skipped because it affected mainly MyISAM tables.

Second idea: Caching effects by either the file system cache caching MyISAM data or the MyISAM key buffer caching MyISAM indexes were examined: File system cache was huge and MyISAM key buffer was only used up to 25%.

I was a bit puzzled...

Configuration of MySQL for Shared Hosting

If you ask around about shared hosting setups with MySQL everybody is frightened. In fact it looks like shared hosting is one of the most difficult setups you can get.

The number of users is big, the number of tables huge and the load pattern is completely unpredictable and the queries often very, let us say: non-optimal.

Here one of the DBA wisdoms come into play: Controlling developers is like herding cats.

If you talk to the Shared MySQL Hoster they confirm that this setups are very demanding!

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