Ryan,
You mentioned the Myosotis project which provides functionality for
PHP and stated that transparent failover is not possible. How is this
so? Can you explain in further detail? I would expect that since the
client apps are making calls to the Sequoia virtual database there
wouldn't be any issues if a backend server were to go down.
Yes, Sequoia will hide all backend failures (as long as there is still
one backend up and running). However, the Sequoia JDBC driver contains
additional failover code that will also hide Sequoia controller
failures. If you don't change the driver on the application side (which
is one of the benefits of Myosotis) you can't have that extra
functionality. As the controller can be collocated with the client
application or the database that might not be an issue depending on your
availability requirements.
All of our database servers reside in a single physical location so
network partitioning is not a concern of ours at this time.
This is good. Still be careful to not introduce artificial partitions
with misconfigured firewalls or VLANs.
One of the notable unsupported items is distributed joins. Are there
any other limitations that you can explain easily via email?
The distributed join limitation only applies to configurations that do
not use full replication (RAIDb-1). But if you want to implement a
production-level HA solution you should go to RAIDb-1 so that limitation
won't apply.
There are limitations with regard to views, triggers and stored
procedures that can break consistency if the controller cannot see the
locks acquired or if indeterministic functions are called by these objects.
Thanks again and I'm sure I'll have additional questions to post to
the list once we get started with our testing. Is the community fairly
active? Why do you state that not many users have been willing to
share their experiences with Sequoia? One of the hesitations my
developers have with deploying this solution is the lack of verifiable
real-world feedback from users.
This is a good question. You can project yourself in 6 months from now
and such email would be posted on the Sequoia mailing list. Would you
read it? And if you are a small shop pressured with deadlines, would you
take time to answer this mail?
The community has a significant turnover as members are fairly active
during their evaluation/deployment phase and then become much quieter
when everything is running. Also since I stopped Sequoia 3 development
not much happened in terms of new features and Sequoia went under a much
needed stabilization period with the 2.10 series.
Now I am resuming the development of Sequoia 4 that should bring new
features and also an open source test suite so that it can be more
easily tested on all databases used out there.
Well I hope I painted a fair picture of Sequoia and its community. Don't
hesitate to post your findings and ask questions as you go.
Best regards,
Emmanuel
Emmanuel Cecchet wrote:
Hi Ryan,
Hello. My company is currently looking to evaluate Sequoia as a
mysql clustering solution and I am wondering if anyone can share
their experiences with the software.
Very few people are willing to share their experience in using open
source Sequoia even though there are quite a bit of production users
out there. However I can tell you what I have seen so far (my opinion
is probably biased since I was the designer of Sequoia ;-)).
We may potentially be rolling out the service in our production
environment and would like to know of any glaring limitations of the
software if there are any. Also, can anyone point me to
configuration documents for getting the software up and running?
You can find the documentation at http://sequoia.continuent.org/Manuals
There is no fundamental difference between 2.x and 3.x but 3.x is now
deprecated and not supported (4.0 is in the works). Config file
format is slightly different.
Besides what the bug tracker can tell you, I would say Sequoia is a
solution that is more geared towards high availability than
performance. Depending on the parallelism you have in your workload
you may see no or little improvement in performance. Note that it is
still the same database that will in the end execute the query, so
individual queries won't execute faster, we just spread the load on
multiple nodes. Writes are replicated on all nodes, so you will never
see improvement on write speed performance.
Sequoia has all the required management mechanics but it does not
provide automated management, you will have to write your own scripts
for that. Continuent provides a commercial product based on Sequoia
that will handle that nicely. If you prefer staying the open source
route, you can seek for help on the mailing list or get help from
consultants (I do consulting ;-)).
How well does the software work with PHP? Most of our backend
systems are tomcat 5.5/6.x but we still maintain legacy PHP software
where needed.
The software was originally designed to work with Java but the
Myosotis project adds direct MySQL protocol support so that you can
run with legacy PHP applications. Just be aware that you won't have
transparent failover with Myosotis. Another option is to use
ODBSequoia, an ODBC implementation if you PHP application uses a db
library that can take an ODBC driver.
Sequoia is highly configurable which sometimes confuses users and can
lead to poor design or integration. We are trying to simplify
configuration for Sequoia 4 but there will still be application
specific optimizations or architectures that cannot be automatically
guessed. One thing to keep in mind is that Sequoia provides
synchronous statement-based replication and the strong consistency
provided does not support network partitions. Therefore, you have to
think twice if you want to use it in a WAN environment.
If some of the things I mentioned are not clear to you or don't ring
a bell, you can read this article that should give you an overview of
the problems you are going to face depending on what solution you go
for (Sequoia or not): http://infoscience.epfl.ch/record/118488
Thanks for your interest in Sequoia,
Emmanuel
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