Fwd: [Zope] (no subject)

[Federico Di Gregorio]

> fog@mixadlive.com said:
> > if you want to use the per-cursor commit extension of psycopg, you
> > need to call the .commit() method on the *cursor*. calling it on the
> > connection will commit on all the cursors derived from the connection.
> 
> I know (I wrote ODBC drivers for a living, among others a PostgreSQL one
>  :-)). I sorta expected the Z SQL Connection to do the "right thing", but it
>  forwards the TM messages to the connection, not to individual cursors.

zope has to cope with drivers that are *not* thread safe at level 2 (see
the Python DBAPI) and the cursor commit is an extension, not implemented 
by other drivers. so Zope does the right thing and uses 1 connection
per thread. 

> > mmm... i think that zope instantiate a connection for every thread. in
> > the psycopg case, every zope thread gets one connection and one
> > cursor.
> 
> Let's hope so, although I haven't been able to discern the code that does
>  that bit of magic. Is there a document somewhere that describes what Zope
>  does, thread-wise, when handling requests?

Zope documentation is, mmm... i little bit difficult to find. usually i
just read the sources and cross my fingers...
 
> Anyway, I plunged into my code and FYI, this is how I'm now dealing with it:
> 
> - select statements grab and release a cursor;
> - update statements grab a cursor, wrap them in a TM subclass and register
>  the result with the transaction manager. The cursor is also registered in a
>  thread map, so that subsequent update statements in the same
>  thread/transaction reuse the cursor. When the Zope TM calls
>  finish()/abort(), the cursor is committed and released (and removed from the
>  thread map).
> - session access (updating the "last accessed" timestamp on mostly every
> request) is done through a special global cursor, which does a commit every
>  10 or so updates keeping disk write load for this non-critical piece of
>  information low.
> 
> The end result is acceptably low connection usage and correct transaction
> scoping.

pretty nice! will this stuff be released in a Zope Product?

ciao,
federico

-- 
Federico Di Gregorio
MIXAD LIVE Chief of Research & Technology              fog@mixadlive.com
Debian GNU/Linux Developer & Italian Press Contact        fog@debian.org
  Qu'est ce que la folie? Juste un sentiment de liberté si
   fort qu'on en oublie ce qui nous rattache au monde... -- J. de Loctra