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



Hi Robert,

First of all, thanks for your time, I really appreciate it.
I'd like to reply to two separate topics here: first, the objective of my question and second, the cluster-awareness of MySQL and the use of GFS with MySQL.

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.
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)
- 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.

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)

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
--


On 7 Mar 2007, at 18:56, Robert Peterson wrote:

Tom Lane wrote:
Can someone help out this questioner?  I know zip about Cluster.
I looked at the FAQ for a bit and thought that what he wants is
probably doable, but I couldn't tell if it would be easy or
painful to do load-balancing in this particular way.  (And I'm not
qualified to say if what he wants is a sensible approach, either.)
			regards, tom lane
------- Forwarded Message
Date:    Sat, 24 Feb 2007 15:37:17 +0000
From:    Ivan Zoratti <ivan mysql com>
To:      tgl redhat com
Subject: Question on RH Cluster from a MySQL Customer
Dear Tom,
first of all, let me introduce myself. I am the Sales Engineering Manager for EMEA at MySQL. Kath O'Neil, our Director of Strategic Alliances, kindly gave me your name for a technical question related to the use of Red Hat and MySQL - hopefully leading to the adoption of RH Cluster. Our customer is looking for a solution that could provide high availability and scalability in a cluster environment based on linux servers that are connected to a large SAN. Their favourite choice would be to go with Red Hat. Each server connected to the SAN would provide resources to host, let's say, 5 different instances of MySQL (mysqld). Each mysqld will have its own configuration, datadir, connection port and IP address. The clustering software should be able to load-balance new mysqld instances on the available servers. For example, considering servers with same specs and workload, when the first mysqld starts, it will be placed on Server A, the second one will go on Server B and so on for C,D and E. The sixth mysqld will then go on A again, then B and so forth. If one of the server fails, the mysqld(s) is (or are) "moved" on the other servers, still in a way to guarantee a load- balance of the whole system. After my long (and hopefully clear enough) explanation, my quick question is: does RH Cluster provide this kind of features? I am mostly interested in the way we can instatiate mysqld and re- launch them on any other server in the cluster in case of fault. I would be very grateful if you could help me or address me to somebody or something for an answer.
Thank you in advance 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

Hi Tom, Ivan, and linux-cluster readers,

In theory, our Piranha / LVS (Linux Virtual Server) may be used to
load-balance the requests to numerous mysql servers in a cluster.

Our rgmanager can provide the High Availability to fail over
mysql services to other nodes in the cluster if they fail.

However, if the mysqld daemons are all running on a SAN and you're
mysqld daemons are trying to serve data from the same file system, you
probably have a problem.  To share the data/database on the SAN in
one harmonious file system, you could use the GFS file system, but "regular" mysql is not cluster-aware (to the best of my knowledge). The sum of my understanding about this may be found here:

http://sources.redhat.com/cluster/faq.html#gfs_mysql

Since Ivan works for mysql, perhaps he can clear this up if
it's not accurate.  I'd like to know more about "mysql-cluster"
and how it's implemented.  I'd like to see mysql implemented as
a cluster-friendly app using our cluster infrastructure so they
can effectively compete against Oracle RAC without reinventing
the wheel. I'd even like to be a part of the effort to make this happen. Hope this helps.

Regards,

Bob Peterson
Red Hat Cluster Suite


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