[DBD-SQLite] DBI, DBD::SQLite and threads

[Tim Bunce]

On Mon, Mar 19, 2012 at 08:42:04AM +0000, Martin J. Evans wrote:
> On 19/03/12 04:19, Adam Kennedy wrote:
> >I've noticed there's a lot of movement at the moment on DBI, threading
> >and performance.
> >
> >http://www.martin-evans.me.uk/node/131
> 
> The issue here was that when using a threaded Perl the state structure
> had to be protected and there was a slow and a faster way of accessing
> it. Some DBDs were using the slow method.

("protection" isn't the issue, it's simply that in a threaded perl
there's one 'DBI State' structure per thread and it's important that the
one for the current thread is used.)

> >In Padre we've always stuck to the use of DBI only in the parent
> >thread, but the time is fast approaching where it would be very handy
> >to run multiple database connections for things like background
> >indexing of code and the like.
> 
> When you build DBI it still says:
> 
> *** You are using a perl configured with threading enabled.
> *** You should be aware that using multiple threads is
> *** not recommended for production environments.
> 
> but I'm unsure to what degree this still applies.

I think that could be removed, at least for recent perls.
I wonder if there's some version where a good number of thread issues
got fixed. Perhaps 5.10, 5.12? Would anyone using thread havily care to
venture an opinion?

> >I was wondering if anyone has any experiences with DBD::SQLite and
> >threads, or can speak with some authority on where we are with regards
> >to them (I do know that the CLONE method seems to blank out the driver
> >structure forcing it to load again in the new thread).

I think that's needed. Certainly handles created in one thread can't be
used in another (the DBI dispatcher will detect that and throw an error).

> >Regardless of whether they currently work or not, I'd like to be able
> >to write a =head2 section in the POD documentation stating our current
> >position on threads and recommendations before the next release.
> >
> >If they can be used in threads, it would be nice to be able to write a
> >DBD::SQLite::Cookbook entry on using threads.
> >Adam K
> 
> I'm afraid I neither use a Perl with threads enabled or threads -
> which is a shame as I didn't see any benefit from that huge change to
> DBD::Oracle.

Many people will benefit. Thanks again.

> I note DBD::SQLite does not seem to be using the DBIS macro so there
> is nothing to change.

Agreed. It looks clean to me.

Tim.