Mike AstleYAPC::Europe 2008

Copenhagen

http://artport.whitney.org/commissions/codedoc/Paley/CodeProfiles_800x600.htm

Profiling Perl

Profiling?● Recording / analyzing timing information about

program execution● General case code profilers record data by line,

sub, source file, etc. - inclusive vs. exclusive timings

● Domain-specific profilers record data about specific event types (e.g. SQL queries)

Some Ways Are More Equal Than Others

Devel::NYTProf – The New Hotness● Improved accuracy – Devel::DProf suffers from

a serious timing issue that makes its usefulness questionable

● Block level profiling – a Perl first● By far the most convenient and useful output

format – very much in keeping with the “Beautiful Perl” theme

● Good mod_perl integration

● Recursion causes over-counting of sub inclusive times – this can bite you hard

● Thread unsafe● caller() issue before 5.8.8● Does not count calls as a result of operator

overloading● goto &$sub not recognized as a sub call● no Windows support● Other suspicious output – got tests?

NYTProf - Open Issues

DBI::Profile and friends● DB usage is one of the most common forms of

optimization● Similar to a generic profiler, but with some very

DBI-specific parts● Impressive options list, easy to use

use DBI;

my $dsn = "DBI:mysql:database=” .

“uk_realestate;host=127.0.0.1;” .

“port=9308";

my $dbh = DBI->connect($dsn, 'root', '');

my $sth =

$dbh->prepare( 'select * from listings' .

' where id = ?' );

$sth->execute( 'id1' );

astle@mirth:~$ DBI_PROFILE='2' perl myprog.pl

DBI::Profile: 0.004590s (12 calls)

myprog.pl @ 2008-07-30 20:28:31

'' =>

0.004049s / 8 = 0.000506s avg

(first 0.003903s, min 0.000002s,

max 0.003903s)

'select * from listings where id = ?' =>

0.000541s / 4 = 0.000135s avg

(first 0.000068s, min 0.000018s,

max 0.000419s)

astle@mirth:~$ DBI_PROFILE='2' perl myprog.pl

DBI::Profile: 0.004481s (12 calls) myprog.pl

@ 2008-07-30 20:31:18

'' =>

'FETCH' => 0.000002s

'STORE' => 0.000114s / 4 = 0.000028s avg

(first 0.000011s, min 0.000008s, max 0.000086s)

'connect' => 0.003811s

'connected' => 0.000007s

'disconnect_all' => 0.000012s

'select * from listings where id = ?' =>

'DESTROY' => 0.000057s / 2 = 0.000028s avg

(first 0.000021s, min 0.000021s, max 0.000036s)

'execute' => 0.000406s

'prepare' => 0.000072s

With a little help from my friends● DBI::ProfilerDumper – writes out all timing data

to a file that can later be analyzed with CLI tool dbiprof

● DBI::ProfilerData – make your own output format

● DBI::ProfileDumper::Apache – you guessed it

DashProfiler

● A fast, lightweight instrumentation system● Built on DBI::Profile● Nothing is “free” – you have to set the data

collection points● Less overhead than a general profiler● Appropriate for live, code that must run fast● Happily gets on with mod_perl as well

use DashProfiler;

DashProfiler->add_profile( foo => { } );

DashProfiler->add_profile( foo => {

granularity => 10,

flush_interval => 600,

flush_hook => sub { ... },

sample_class => ‘DashProfiler::Sample’,

dbi_profile_class => ‘DBI::Profile’,

period_exclusive => ...,

period_summary => ..., } );

package MyModule;

use DashProfiler::Import

foo_profiler => [ ‘bar’ ];

sub my_sub {

my $value = shift;

my $sample = foo_profiler( $value )

if foo_profiler_enabled();

...send to $hostname...

}

DBI::Profile: 0.000027s 0.00% (2 calls) test-dash.pl @ 2008-08-12 13:32:15

'bar' =>

'baz' =>

0.000027s / 2 = 0.000013s avg

(first 0.000013s, min 0.000013s,

max 0.000014s)

● Fixes to known NYTProf problems

● Even more beautiful profiler output and visualizations

● More tests!● sub-microsecond

precision for DBI::Profiler

The Future?

Tak!

astle@lokku.com