Comments on: Opening Tables scalability

By: Andreas Bergman

Andreas Bergman — Sun, 11 Dec 2011 20:44:24 +0000

Hi,

Do you know if this issue is fixed in 5.5?

We run a WP multisite with about 200k tables and as tables in open_table cache increase the execution time of the query increase and at last there is always 400 querys running and most of them in opening/closing state. If I restart the process it works like a charm for a couple of hours, and then it starts all over again.

Any ideas?
Andreas

By: Sergei

Sergei — Mon, 10 Oct 2011 23:53:15 +0000

And I was wondering if MySQL can handle a few thousands of tables. Compared to wordpress’s numbers, this is like a toy project

By: Mattias J

Mattias J — Mon, 28 Feb 2011 11:28:22 +0000

We have some 2000 databases with the same set of 250+ tables (both numbers constantly growing) = 500’000 tables and counting on the same server.

As we are trying to scale out, our main options seems to be either “manually” partition different databases to different servers, or putting all the data in a single set of large tables in combination with built-in MySQL Partitioning.

But how does MySQL Partitioning affect table opening / tables cache???

Are there other options we should consider?

By: Derek Organ

Derek Organ — Tue, 27 Oct 2009 15:42:09 +0000

We work on the basis of a different database for each new company account. The problem I’m starting to have with 5000 databases is the show databases and use database commands are taking a long time to run and are showing up in my slow-queries log. Are there any tips for making this go faster?

By: My “hot” list for next InnoDB features | MySQL Performance Blog

My “hot” list for next InnoDB features | MySQL Performance Blog — Tue, 31 Mar 2009 21:48:29 +0000

[...] bad at start time, when InnoDB takes probes during opening table, as it is slow operation. See also http://www.mysqlperformanceblog.com/2006/11/21/opening-tables-scalability/. Partially it can be fixed by recent patches by enabling / disabling probes and changing count of [...]

By: peter

peter — Thu, 17 Apr 2008 16:31:56 +0000

MySQL only opens tables once you access them.

By: art

art — Thu, 17 Apr 2008 11:13:37 +0000

Does mysql open all innodb tables at startup or only with query on that particular table?

By: Sysadm

Sysadm — Tue, 20 Mar 2007 19:29:05 +0000

We have forum hosting community – around 3 500 000 myisam tables per each server. Each forum gets it’s own database (~90 tables in one database) . We have similar issue – when server is overloaded, status of all threads in “show processlist” is “opening tables”. We have many php and system tweaks but this problem seems to be hard to resolve without MySQL source code rewrite -we have not enought knowledge to do it. It’s MySQL 4.0.

We have tried to increase table_cache but it doesn’t make any sense with such many useable tables – best performance setting for us is table_cache=0.

Now it’s hosted on Linux 2.6 & XFS which supports more than 32K subdirectories in one directory. Reiserfs supports too, but it’s terribly unstable within such load and brokes it’s journal itself very often, and reiserfs is not visible faster in this than XFS.

I’m afraid of putting such many tables into one database – this cause worse performance problems – like hosting >10 000 000 files in one directory (3 files per table)…

By: peter

peter — Sun, 11 Mar 2007 12:49:23 +0000

This actually was always curious for me why WordPress MU was not fixed to operate with smaller amount of tables rather than create single table set for each users.

You can blame MySQL for certain performance problems but generally dealing with a lot of files is slower with most of file systems.

By: Hakan

Hakan — Sun, 11 Mar 2007 10:25:20 +0000

WordPress.com hosts a free blog system running WordPress Mu (multiuser wordpress) and it creates a new set of tables for every new blog.

/Hakan