Re: fleeing sql

On Wed, 2007-08-08 at 12:34 -0700, abused by speech recognition wrote:
> If I remember correctly, metakit is multi-reader single writer right?
> since I need multi-writer, guess I'm best solving that with embedding
> metakit in a server using internal access locks?  does metakit work in
> a python multi threaded environment either as multi thread access or a
> single thread fed by multiple request threads/
> 
> thanks for any feedback

In a python single-process multi-threading environment, I'm sure that
metakit could be made to work well, even if you have to surround the
access statements in each thread with .acquire() and .release() of a
threading.Lock object.

I'm also interested in a multi-process scenario, such as CGI-based web
server. This could be made to work well by tuning the http
request/response cycle:

 - create a metakit.storage() object at start of the http response
   cycle, with the database open in read mode

 - for a very small part of the http response cycle:
     - acquire a file lock on the metakit database file
     - create another metakit.storage() object on the file, this one
       with the database open in read/write mode
     - perform all needed write operations
     - commit() the the read-write storage object
     - del the read-write storage object
     - release the file lock

 - continue with the rest of the http response cycle, using the
   read-only instance of the storage object

The smaller the 'write window', the less the performance impact in a
busy server environment.

My questions on this scenario:
 - would it work?
 - would there be any problems with having two different metakit.storage
   objects open at the same time in the same process, one with readonly
   access and one with read/write access?
 - how would it compare, performance-wise, to a DB built for concurrency
   such as MySQL?

Cautions with this approach:
 - all View and row objects acquired from the read-write storage object
   would have to be freed (ie, not stored in any object instances or
   globals or closure-locals spaces) prior to doing the commit

Metakit can offer significant speed and simplification over *SQL
databases. Mk4Py allows a friendly object interface to views and rows,
where to get the same for *SQL databases, one needs to load in something
like SQLObject, which is hugely expensive.

I would be interested in people's thoughts on all this.

Cheers
David

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