[Linux-cluster] Cluster vs Distributed? & MySQL Cluster?

[David Brieck Jr.]

On 10/25/06, isplist at logicore.net <isplist at logicore.net> wrote:

> PS: I saw someone asking about sharing data on MySQL, that's something I'd
> love to do. In fact, I'd like to get rid of the big box IBM servers over using
> smaller blade servers. Problem is, the blade servers don't allow for much
> memory, from 512 to 2GB. the IBM's allow for 5GB's. But I wonder if I could
> still get away with many low memory MySQL servers sharing GFS storage?
> I would guess that one or more would write but that many could read.
>
> Mike
>

So far things seem to be working fairly well with multiple active
MySQL servers. You can't use the query cache (for obvious reasons) and
you can't use innodb tables but for the most part it's working well.
The one thing I ran into that I didn't anticipate was that after you
add, edit or remove a user or grants you need to flush the privileges
on all the server manually. I haven't found a configuration option to
tell MySQL not to cache those values so I'll probably just have to
either modify my scripts to automatically flush after these actions or
just have a cron job running on the nodes every 10 minutes or so to
keep everything in sync.

I did manage to get LVM DR working after some trouble initially. One
thing I should note, you probably want to enable persistence,
otherwise you really seem to take a performance hit.

Here's the script I use to check to see if a server is alive:

#!/bin/sh

TEST=`/usr/bin/mysqladmin --user=piranha --password=piranha ping
--host=$1 | grep -c "mysqld is alive"`

if [ $TEST == "1" ]; then
        echo "OK"
else
        echo "FAIL"
fi



One thing about servers with smaller amounts of RAM: it won't matter
how many small servers you have if you have queries that constantly
have to load large tables (mainly for sorts) into memory and you don't
have that much your server will probably crawl.

I should note we're just running our DNS servers (MyDNS) and our
spamassasin database on it, but so far no problems. It was even
inadvertently tested on night and everything worked perfectly. We'll
know more once some of our larger databases are moved over.