Le 2011-10-28 01:01, Clint Byrum a écrit :
Excerpts from Filipus Klutiero's message of Thu Oct 27 16:49:30 -0400 2011:
Package: mysql-server-5.1
Version: 5.1.58-1
Severity: wishlist
Hi,
I'm opening a ticket about a general problem, but this is food for
thought too. Please apologize and triage as you wish.
I am a web developer working on a web application which has a large
schema. There are currently over 200 tables in the schema, all of them
MyISAM.
Every few weeks, I'll install a new version of the application and
create a new MySQL database for it.
My development desktop was installed in April 2010, and has been getting
slower and slower to boot, to the point where I'm thinking about
reinstalling since months. There is a lot of disk read during boot, and
I never knew precisely why. Today I realized by accident that mysqld was
taking about 10% CPU for a very long time during boot, and went to
investigate why.
Restarting mysql seems to happen fast (less than 5 seconds), but it was
in fact causing significant CPU usage for a long time. I found that this
CPU usage happened every time mysql was started, and then that this came
from /etc/mysql/debian-start. I then discovered it came from
check_for_crashed_tables(). The function contains:
My first question would be why are you using MyISAM for anything
important. Or rather, why are you using MyISAM, at all. I know that
we are still stuck with MySQL 5.1 and, therefore, have MyISAM as the
default, but its become quite obvious that it is such a limited data
storage engine, that it should not be used by any serious application.
Hehe. I think that suggests the answer :-) The application's next
version *will* introduce InnoDB support, but only experimental. There
are still features missing in InnoDB in our minimal required MySQL
version (5), although we're also working on moving from FULLTEXT search.
I would recommend that you alter all of your tables to InnoDB, and start
explicitly setting the engine to InnoDB during your create tables. You
will get a far more resilient system with nearly the same speed on most
common sane operations. There is no need to check these tables, because
like a journaled filesystem, one can trust that the database is in a
consistent state or not just by looking at the headers and journals.
Thanks. I'm aware that using InnoDB would solve this problem, but our
past versions don't support InnoDB. I am planning to review the InnoDB
support which was introduced when I have the opportunity, and hopefully
I can start testing it.
BTW, I forgot to mention that I am not a database expert at all, so not
in a good position to judge whether the time to check a MyISAM table is
reasonable or not.
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