At 11:25 1-2-2000 -0600, Leslie Mikesell wrote:
>According to Elizabeth Mattijsen:
>
> > We have been using such a setup for over 2 years now. The only real issue
> > we've found is not so much with mod_perl itself, but with MySQL. If you
> > put your databases on the NetApp, either have a seperate central database
> > server, or make damn sure you do not use the same database from two
> > different front-end servers. We've seen database corruption that way
> > (using Linux front-end servers with NFS 2).
>
>It is probably reasonable for MySQL to assume that only one server
>is accessing the files at once since it has its own remote client
>access protocol. Do you happen to know if there is a performance
>difference for MySQL between local drives and a NetApp?
All MySQL operations are atomic. You can always be sure that no two threads
will be updating a table at the same time, for example. If you need to work
on multiple tables while making sure data stays consistent among them, lock
these tables before use.
A single MySQL server will have no problems running with its databases
mounted on an NFS store, although performance probably won't be very good.
It shouldn't hurt too much for huge tables that you don't access that
heavily, but those that you do use frequently had better be kept on a local
disk. Of course you can just make symlinks in your var directory to the
tables that you've stored on an NFS store somewhere.
Multiple MySQL servers running on the same database stored on an NFS store
is not something you should try at all. Threaded locking is unreliable by
itself on Solaris and Linux if I read the MySQL docs correctly, and NFS
locking is worse than that. You'd absolutely need a thread-safe flock()
implementation that works over NFS as well - good luck with your quest. :)
When you do use locking, be very very careful if you use Apache::DBI or
similar persistent connections. MySQL threads keep tables locked until
the thread ends (connection is closed) or the tables are unlocked. If your
session die()'s while tables are locked, they will stay neatly locked as
your connection won't be closed either .... This was a nasty one I bumped
in to ...
Grtz,
Pascal
--
Pascal Eeftinck - arcade^planet.nl
arcade^xs4all.nl - Perl is not a language, it's a way of
life
