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@xxxxxxxxx
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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