HD Mirroring

[Justin Hopper]

On Wed, 2004-11-24 at 23:08, Justin Hopper wrote:
> On Wed, 2004-11-24 at 13:31, Charles Sprickman wrote:
> > On Wed, 24 Nov 2004, Brian Reichert wrote:
> > 
> > > And, although I've not tested it, recent versions of MySQL can
> > > outright support a cluster:
> > >
> > >  http://dev.mysql.com/doc/mysql/en/NDBCluster.html
> > 
> > I'm just curious if there's any other solution that will work on FreeBSD. 
> > I have about 5 mysql servers (4 slaves, 1 master) and one application in 
> > particular is not smart enough to try other servers if the configured 
> > server does not answer.  Is there any type of local proxy that can 
> > intelligently route requests to the "best" server?
> > 
> I too was curious about the MySQL Clustering support and its status on
> FreeBSD, since it wasn't as a supported OS.  Over the last couple of
> hours I was able to set up a cluster consisting of a management process
> and data node running in one jail, and a MySQL server and another data
> node running in a different jail.  Once everything was up and running,
> the cluster seemed to be working excellent, data was synchronizing
> flawlessly throughout the cluster.  Nuking either of the data node
> processes did not affect access to the data in the cluster, so failover
> seemed to be working as well.
> 
> The only problem that I ran into, and it may be user error on my part,
> is that when the cluster is shut down (or all data node processes are
> killed), the data contained in the node is lost when the cluster is
> brought back online.  Perhaps there is some recovery step that is
> required before the cluster can be used again.
> 
> If someone else has already tested MySQL's clustering ability with
> FreeBSD, then please let us know the results so that I don't recreate
> the wheel here.  If not, I'll continue seeing how far I can get with it,
> as I would definitely like to implement this functionality on several of
> the more critical databases that I manage.

I'm sure it's taboo to respond to one's own message, but thought I would
follow up with some information on the problems I was running into with
MySQL Cluster.

The first problem, where it appeared that the data in the cluster was
lost when the cluster was shut down, turned out to be there are some
problems with the MySQL servers, which act as API clients to the
cluster, reliably connecting into the cluster.  Several times I could
not get a MySQL server to connect to the cluster, but found no rhyme or
reason for it so far.  The cluster seems to be retaining data just fine
upon shutdown, when the MySQL servers can actually connect to it to
query data that is...

The second problem I encountered was while trying to load a table that
was 163MB in size that contained around 1 million rows.  The NDB cluster
would continually report that the table was "full" when trying to import
the data.  After checking around on mailing lists, I found out that the
NDB clustering engine will require around table_size*2*10% RAM to load a
table.  NDB keeps all of the data in main memory, and has a fair amount
of overhead per row.

Perhaps somebody else can do a more thorough test of MySQL clustering on
FreeBSD to make sure that it is in fact fully stable.  It seems like a
remarkable system, assuming you have the gigs of RAM it takes to run it
with a table of any substantial size...
-- 
Justin Hopper  <jhopper at bsdhosting.net>
UNIX Systems Engineer
BSDHosting.net
Hosting Division of Digital Oasys Inc.
http://www.bsdhosting.net