Re: Set::Infinite backtrack too deep from DateTime::Set

[Flavio S. Glock]

2007/2/5, Joshua ben Jore [EMAIL PROTECTED]:

I'm using DateTime::Set to encode a radio station's program lineup.
It's about 170 weekly recurrences that are all mostly about an hour
apart.


Set::Infinite can't optimize this query, so it's actually making 170
or more calls to Recurrence and comparing them.

You could get a big optimization by combining several recurrences into
a single set, like:

 my $set = DateTime::Event::Recurrence-weekly(
   days = [ 2, 4 ], hours = [ 10, 14,  -1 ], minutes = [ 15, 30, -15 ]
 );


- Flavio S. Glock

Set::Infinite backtrack too deep from DateTime::Set

[Joshua ben Jore]

I'm using DateTime::Set to encode a radio station's program lineup.
It's about 170 weekly recurrences that are all mostly about an hour
apart. If I try to find the current event it's really slow and I get a
pile of warnings from Set::Infinite. I can get the warnings to go away
if I set $Set::Infinite::max_backtrack_depth to 52. I can get
semi-reasonable performance for the -current call if I restrict the
set being queried to only the recent past.

The warning:
 Set::Infinite: Backtrack too deep (more than 10 levels) at
/home/josh/bin/perl/5.8.8/lib/site_perl/5.8.8/DateTime/Set.pm line 535

I'm hoping someone here can suggest a better way to do this, get
better performance from the -current query, avoid having to manually
guess the range I'll find an answer in, and what's the deal with the
warnings.

 # Look up whatever is current for a date/time.
 $THE_DATE = ...

 $all_events = DateTime::Set-empty_set-set_time_zone( 'US/Central' )
 for ( ... )
 $all_events = $all_events-union(
 DateTime::Event::Recurrence
 -weekly( %$_ )
 -set_time_zone( 'US/Central' )
 )

 local $Set::Infinite::max_backtrack_depth = 52 # Set::Infinite, shut up!

 # Restrict $all_events to only the recent past because this makes
the query faster
 $recent_past = $all_events-intersection(
 DateTime::Span-from_datetimes(
 from = $THE_DATE-clone-subtract( hours = 4 )-truncate(
to = 'hour' ),
 end = $THE_DATE
 )
 )

 $CURRENT = $recent_past-current( $THE_DATE )

Josh