Are the actual data files shared in this setup between the active mysql
daemons?
Last time I looked into this it seemed that with shared-nothing model each
mysql daemon would have to keep it's own copy of the data and updates
would be propagated from active to passive daemons (master-slave model)
or between active daemons (ndb in-ram database model)
Are the mysql daemons running on the GFS I/O nodes that have access to
shared
storage via SAN or iSCSI and coordinate locking through GFS
infrastructure, or are
the mysql daemons running on client nodes that use GFS to remotely
access storage
that is provided by other GFS I/O nodes that in turn have access to shared
storage via SAN or iSCSI?
Michael
David Brieck Jr. wrote:
On 10/25/06, isplist@xxxxxxxxxxxx <isplist@xxxxxxxxxxxx> 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.
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