FAQ
Hi. I don't usually use the "threads" module in my projects, but...

1) DBD::SQLite has several tests that use fork(), that means emulated
fork() (with ithreads) under Windows, and they've been working fine
for years.

2) DBIS/dTHR issue was fixed at DBD::SQLite 1.22_04 (released in
April, 2009) by Tim's advice.

3) Docs on SQLite3's thread safety:
- http://www.sqlite.org/compile.html#threadsafe
- http://www.sqlite.org/c3ref/threadsafe.html
- http://www.sqlite.org/faq.html#q6

4) DBD::SQLite is compiled with the default THREADSAFE option if your
perl supports ithreads, or THREADSAFE=0 (single thread mode)
otherwise.

5) As a general rule, a) you shouldn't use DBI handles prepared
outside the threads, and b) you're advised to set
sqlite_use_immediate_transaction attribute to true (or issue BEGIN
IMMEDIATE) to avoid (dead)locks.

Regards,

Kenichi

(Sorry for dupe, Tim)

2012/3/19 Tim Bunce <Tim.Bunce@pobox.com>:
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.

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