[Zope-DB] Re: SQL Relay

M.-A. Lemburg mal at lemburg.com
Fri Oct 31 06:56:49 EST 2003

Kent Hoxsey wrote:
>>You have to be more specific about the kinds of queries you are running.
>>It is likely that they are imposing exclusive row locks on some of
>>the more important tables in your database.
> I have deep, specific knowledge of the queries I am running. Oracle does not
> impose row locks on tables when reading (select only), it is considered a cardinal
> sin these days for a database server to block on read locks.

So if I understand you correctly, both queries are doing SELECTs only ?!
Locks are usually only imposed on INSERT, UPDATE, DELETE, etc. that
change the database.

> If I were enforcing
> consistent-read transaction isolation on my query, I would expect additional lag
> time as the system managed block copies to the redo logs for rows within my 
> query that were touched by other processes in the system.
> However, I am not concerned about consistent reads, and so log activity is not
> an issue. But more to the point: I am completely comfortable with the issues
> of managing sql queries within Oracle. I do not have a problem with (or at least, 
> have no control over) the response speed for the database query.  I do have
> a problem with Zope's seeming inability to serve pages when more than one
> ZSQL method is running.
> To re-state the problem: Zope will not serve an index_html request once I start
> a second ZSQL method running.

I've never seen such a problem with Zope before, so this must
be related to the settings on your database or the database interface
you are using, e.g. there might be calls to C APIs that the underlying
Oracle interface blocks when running the query and that the interface
does not release the global Python interpreter lock for.

I'd suggest you connect to the Zope process using gdb or a
similar debugger and check where the threads are spending all
their time.

If there's something we could do in the mxODBC Zope DA to help
prevent the problem, we'd be most happy to do so.

Marc-Andre Lemburg

Professional Python Software directly from the Source  (#1, Oct 31 2003)
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