[ZODB-Dev] ZEO and relstporage performance

[Ross J. Reedstrom]

On Tue, Oct 13, 2009 at 06:30:31PM -0600, Shane Hathaway wrote:
> Laurence Rowe wrote:
> > Shane's earlier benchmarks show MySQL to be the fastest RelStorage backend:
> > http://shane.willowrise.com/archives/relstorage-10-and-measurements/
> 
> Yep, despite my efforts to put PostgreSQL on top. :-)  It seems that 
> PostgreSQL has more predictable performance and behavior, while MySQL 
> wins slightly in raw performance once every surprisingly slow query has 
> been optimized.

The usual wisdom on that is MySQL is faster at raw table reading,
PostgreSQL at concurrency, esp. w/ any writing thrown in. Often, the
performance curves 'cross' at some point. Could be > 16 in this case. 

For my druthers, I just _trust_ PostgreSQL a lot more: the one MySQL DB
I have that I use on an on-going basis is my MythTV media-pc. Once a
month or so I have to repair a table. I've used PostgreSQL in
professional high load production for years and never had a corruption
issue: even when running out of disk! (the main culprit in my experience
w/ MySQL, since that's the default state for a PVR: full!)

<snip caching discussion>

> 
> This leads to an interesting question.  Memcached or ZEO cache--which is 
> better?  While memcached has a higher minimum performance penalty, it 
> also has a lower maximum penalty, since memcached hits never have to 
> wait for disk.  Also, memcached can be shared among processes, there is 
> a large development community around memcached, and memcached creates 
> opportunities for developers to be creative with caching strategies.

shared caches: this is the main reason I've been looking at relstore:
we're running many Zope FEs against one ZOE right now, and due to the
nature of the load-balancer, we're seeing little gain from the caches.
I'm looking to fix that issue, to some extent, but sharing across all
the FEs on one box would be a big win, I'm sure.

> So I'm inclined to stick with memcached even though the ZEO cache 
> numbers look better.

Ross
-- 
Ross Reedstrom, Ph.D.                                 reedstrm at rice.edu
Systems Engineer & Admin, Research Scientist        phone: 713-348-6166
The Connexions Project      http://cnx.org            fax: 713-348-3665
Rice University MS-375, Houston, TX 77005
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