Re: [Linux-cluster] FWD: Question on RH Cluster from a MySQL Customer

[Wendy Cheng <wcheng redhat com>]

Robert Peterson wrote:
> Ivan Zoratti wrote:
> > My original question was mainly related to the use of Piranha to 
> > switch over a service (ie, a specific mysql daemon) from one server 
> > to another, in case of fault. There should be only one active service 
> > in the cluster, therefore no concurrency or locking issues should 
> > happen.
I assume this is a special daemon (say the one controls meta data) among 
many other mySQL daemons ?

> > The ideal system should be able to:
> > - have a list of services to launch on the cluster
> > - identify the node in the cluster suitable to host the service (for 
> > example the node with less workload)
The only load balancer we have (at this moment) indeed is piranha (LVS). 
However, using load balancer combining with GFS is tricky due to locking 
overhead (cluster locks are expensive). We do encourage individual file 
access to stay within one node for a proper length of time if all 
possible. Judging by your above statement, since switching (that 
particular ?) service only happens upon fault, this should be ok. 
Current versions of rgmanager and GFS out in the field do not have 
workload statistics - so knowing which node has less workload would be 
tricky (unless you put LVS as the front end). The newest version of 
cluster software using openais (Steve Dake, cc in this email, is the 
maintainer) that may have some features that can be used (but I'm not 
sure).

-- Wendy
> > - check the availability of the service
> > - stop the service on a node (if the service is not already down) and 
> > start the service on another node in case of fault
> > Fault tolerance in this case will be provided by the ability to 
> > switch the service from one server to another in the cluster.
> > Scalability is not provided within the service, ie the limitation in 
> > resources for the service consist of the resources available on that 
> > specific server.
> >
> > I understand that your cluster suite can provide this functionality. 
> > I am mainly looking for a supported set of features for an enterprise 
> > organisation.
>
> Red Hat's Cluster Suite does all of this with the rgmanager service
> (not piranha).  I guess I'm not sure what you're asking here.  Are you
> asking what features rgmanager has?  Its features are probably documented
> somewhere, but I don't know where offhand.  I know it's quite
> full-featured and allows you to do exactly what you listed:
> provide High Availability (HA) of multiple services, stopping and
> starting services throughout cluster, with different kinds of
> dependencies.  The Cluster FAQ has information on rgmanager here
> that you may find helpful:
>
> http://sources.redhat.com/cluster/faq.html#rgm_what
>
> If you have questions that aren't covered by the FAQ, let me know and 
> I'll do my best to answer your questions.
>
> > The second topic is related to the use of MySQL with clusters and 
> > specifically with GFS. It is what we use to call MySQL in 
> > active-active clustering. I am afraid your documentation is not 
> > totally accurate. Unfortunately, information on the Internet (and 
> > also on our web site) are often contradictory.
> > It is indeed possible to run multiple mysqld services on different 
> > cluster nodes, all sharing the same data structure on shared storage, 
> > with this configuration:
> > - Only the MyISAM storage engine can be used
> > - Each mysqld service must start with the external-locking parameter on
> > - Each mysqld service hase to have the query cache parameter off 
> > (other cache mechanisms remain on, since they are automatically 
> > invalidated by external locking)
>
> Thanks for providing this information.  I'll get it into the cluster FAQ.
> Maybe some day I'll find the time to play with this myself.
>
> > I am afraid this configuration still does not compete against Oracle 
> > RAC. MySQL does not provide a solution that can be compared 1:1 with 
> > RAC. You may find some MySQL implementations much more effective than 
> > RAC for certain environments, as you will certainly find RAC 
> > performing better than MySQL on other implementations.
> >
> > Based on the experience of the sales engineering team, customers have 
> > never been disappointed by the technology that MySQL can provide as 
> > an alternative to RAC. Decisions are based on many other factors, 
> > such as the introduction of another (or a different) database, the 
> > cost of migrating current applications and compatibility with third 
> > party products. You can imagine we are working hard to remove these 
> > obstacles.
> >
> > Thanks again for your help,
> >
> > Kind Regards,
> >
> > Ivan
> >
> > --
> >   Ivan Zoratti - Sales Engineering Manager EMEA
> >
> >   MySQL AB - Windsor - UK
> >   Mobile: +44 7866 363 180
> >
> >   ivan mysql com
> >   http://www.mysql.com
>
> If you have other questions, please let me know.  You can either
> email me directly or join the linux-cluster mailing list where you can 
> talk to people are using these features and everyone can benefit from 
> the discussion.
>
> Regards,
>
> Bob Peterson
> Red Hat Cluster Suite
>
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