As many of you probably know, the current find_or_create()
implementation contains a race-condition.
Catalyst::Plugin::Session::Store::DBIC is especially prone to die in
front of the user when using the flash() method - even more so when
AJAX calls are involved resulting in two or more concurrent requests
trying to select/insert the flash data into the database via
find_or_create().
I proposed the following reverse order implementation on the Catalyst
mailing list which will hopefully not only reduce the probability of a
race-condition but will also reduce find_or_create() to a single query
in the best case.
On Tue, Jul 29, 2008 at 12:49:17PM +0200, Tobias Kremer wrote:
Maybe it'd be better to ditch find_or_create in favor of something
like this:
eval {
$row = $self->model->create( { ... } );
}
if( $@ && $@ =~ /duplicate/ ) { # the question about detecting this
remains
$row = $self->model->find( { ... } );
}
This would reduce the query to 1 at best and 2 at worst.
mst responded with:
On 30.07.2008, at 12:26, Matt S Trout wrote:
It's still probably viable.
What I'd really like is to add some code to DBIC's storage to know
what re
that /duplicate/ is on whatever DB so we can bury this away from the
user
and DBIC can Just Use It for find_or_create on any supported database.
Maybe you could wander over to the DBIC list and poke at patching that
instead?
So, the problem is: How to detect if the insert failed due to a unique
key constraint for all supported databases?
I'd volunteer to help implementing this but as of now I'm not that
deep into DBIC to know exactly how to pull this off. So I'd really
appreciate a few ideas and thoughts.
I suppose we could put a method returning a database-dependent regular
expression that detects unique key constraint errors into the
DBIx::Class::Storage::DBI::* classes and use that from within
find_or_create().
What do you think?
--Tobias
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