Hey,
When I profiled my "read CSV, munge, write CSV" script to see why it is a bit
on the slow side DateTime.Str stood out. I saw the default formatter eventually
reached sprintf, which consumed a lot of time. Each output line from my script
has one date and time in ISO 8601 format, and when I changed the script so that
they were stringified without sprintf the total runtime dropped from ~7 to ~4.5
seconds on a short run that converts 800 lines to 1100.
A test case for this:
#!/usr/bin/env perl6
# Arg: Quick DateTime
sub MAIN( :$qDT = False ) {
while my $x++ < 1000 {
say DateTime.new( year => 2017, hour => (^24).roll, minute =>
(^60).roll,
formatter => ( $qDT ?? &formatISO8601 !! Callable ) );
}
}
sub formatISO8601( DateTime $dt ) {
( 0 > $dt.year ?? '-'~ zPad( $dt.year.abs, 4 ) !!
$dt.year <= 9999 ?? zPad( $dt.year, 4 )
!! '+'~ zPad( $dt.year, 5 ) ) ~'-'~
zPad( $dt.month, 2 ) ~'-'~ zPad( $dt.day, 2 ) ~'T'~
zPad( $dt.hour, 2 ) ~':'~ zPad( $dt.minute, 2 ) ~':'~
( $dt.second.floor == $dt.second
?? zPad( $dt.second.Int, 2 )
!! $dt.second.fmt('%09.6f') )
~
( $dt.timezone == 0
?? 'Z'
!! $dt.timezone > 0
?? ( '+' ~ zPad( ($dt.timezone/3600).floor, 2 ) ~':'~
zPad( ($dt.timezone/60%60).floor, 2 ) )
!! ( '-' ~ zPad( ($dt.timezone.abs/3600).floor, 2 ) ~':'~
zPad( ($dt.timezone.abs/60%60).floor, 2 ) ) )
}
sub zPad($s, $p) {'0' x $p - $s.chars ~ $s}
Running that with —qDT results in a bit less than a 4x speedup for me, with
results piped to /dev/null. I wouldn’t know whether doing something like this
in general is a good idea, of if sprintf/fmt should be improved.
Putting together that example, I noticed that Date.today also seems slow,
taking about twice as long as DateTime.new. Replacing "year => 2017” with "date
=> Date.today" in the example above slows it down by about 400ms on my (slow)
laptop computer. I don't call that in a loop like in this in my actual script
anyhow, so that's no biggie for me, but it’s the sort of thing that might get
put in a tight loop so it’s something to be aware of.
-------
Thor Michael Støre
[email protected]
Database guy in Kongsberg, Norway
Mobile: +47 97 15 14 09
