[Zope] ZODB or xySQL?

[Andy Dustman]

On Wed, 15 Mar 2000, Tony McDonald wrote:

> If you get Andy Dustmans' MySQLdb Module 
> (http://www.zope.org/Members/adustman/MySQLdb). It's designed to be 
> thread-safe. I've always taken that to mean that if a Zope request 
> does a ZSQL query that uses this module, then if another ZSQL query 
> comes along (in a different Zope thread) then it is *not* blocked 
> until the first query is finished, but runs alongside the first query.
> 
> If I'm wrong on this I would *really* appreciate a correction here.

I think that's probably wrong. The thread-safety-ness of MySQLdb is that
two threads can share the module. You can't safely share connections, but
this is more of a MySQL limitation than a MySQLdb limitation. Of course,
you can share connections if you wrap a mutex around it so that only one
thread uses it at a time, but it is far better to have multiple
connections: Each connection is a seperate MySQL thread on the server
side.

The old MySQLmodule was probably thread-safe, but not thread-friendly: If
you ran a blocking operation (like a query), it would block all the
threads (i.e. it did not give up the Python interpreter lock during
blocking calls). This apparently causes really bad performance with Zope.

I may be deficient on Zope zen, but it seems like you would definitely
want to have several connection objects around, perhaps one for each ZSQL
Method, so that these can all work in parallel. From a security
perspective (i.e. you aren't just paranoid, you know they are out to get
you), this may make sense, as you can set up seperate users in MySQL with
very specific privileges, so each connection object can only do one thing
and can't be hijacked for something else.

-- 
andy dustman       |     programmer/analyst     |      comstar.net, inc.
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