We just made some tests with MongoDB. As we use PHP and Perl as main languages, we decided to benchmark both on a very simple case: inserting 10.000.000 entries.
The PHP script we use, mongo_pain.php:
< ?php
$m = new Mongo();
$db = $m->db_bench;
$collection = $db->tphp;
$num = 10000000;
while ($num-- > 0)
{
$collection->insert(array('idfox' => $num,
'idxxxxxx' => 'outchagaloup',
'idxxxxxxref' => 0,
'value' => 'no_rice_without_price',
'datetime' => 'newDate()',
'date' => '2011-03-20',
'time' => '17:00:00'));
}
exit;
?>
And the Perl version, mongo_pain.pl:
#!/usr/bin/perl
use 5.010;
use strict;
use warnings;
use MongoDB;
$MongoDB::BSON::utf8_flag_on = 0;
my $MONGO_HOST = 'localhost';
my $MONGO_PORT = 27017;
my $mongo = MongoDB::Connection->new(host => $MONGO_HOST, port => $MONGO_PORT);
my $mongo_database = $mongo->db_bench;
my $mongo_collection = $mongo_database->tprl;
my $num = 10_000_000;
while ($num-- > 0)
{
$mongo_collection->insert(
{
idfox => $num,
idxxxxxx => 'outchagaloup',
idxxxxxxref => 0,
value => 'no_rice_without_price',
datetime => 'newDate()',
date => '2011-03-20',
time => '17:00:00',
});
}
We were very surprised by the results…
> time php mongo_pain.php php mongo_pain.php 101,45s user 9,33s system 43% cpu 4:16,44 total
and
> time ./mongo_pain.pl ./mongo_pain.pl 335,99s user 100,80s system 95% cpu 7:37,88 total
Big difference!!!
During running, a top for each launch gives for PHP:
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 30055 root 40 0 31.3g 6.2g 6.2g S 100 39.4 11:38.90 mongod 14787 root 40 0 116m 9320 5884 R 57 0.1 0:43.74 php
and for Perl:
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 17405 root 40 0 47332 10m 2456 R 100 0.1 0:42.64 mongo_pain.pl 30055 root 40 0 33.3g 6.1g 6.1g S 76 39.0 14:16.58 mongod
We use PHP 5.3.5 and Perl 5.10.1 under a debian lenny on a xeon E5405 (8 core) with 16G of memory and SSD disk.
To try to understand, we profiled the perl script with the excellent Devel::NYTProf reducing the number of inserts from 10.000.000 to 1.000.000.
perl -d:NYTProf mongo_pain.pl && nytprofhtml
You can browse the results here.
Most of the time is spend in MongoDB::Collection::batch_insert, which calls MongoDB::write_insert and MongoDB::Connection::send. These functions are XS ones, too bad…
We have to investigate in C code…
Before doing that, we just stace‘d each execution. The fact that the perl client was at 100% of CPU while mongod stayed around 75 can tell that it don’t wait correctly for IOs.
strace -p $PID -ttt on PHP script execution:
1301070012.395152 sendto(3, "\320/!\n\322\7db_bench.tph"..., 208, 0, NULL, 0) = 208 1301070012.395205 time(NULL) = 1301070012 1301070012.395239 time(NULL) = 1301070012 1301070012.395270 sendto(3, "\320000!\n\322\7db_bench.tph"..., 208, 0, NULL, 0) = 208 1301070012.395324 time(NULL) = 1301070012 1301070012.395357 time(NULL) = 1301070012 1301070012.395388 sendto(3, "\320001!\n\322\7db_bench.tph"..., 208, 0, NULL, 0) = 208 1301070012.395442 time(NULL) = 1301070012 1301070012.395475 time(NULL) = 1301070012 ...
and on perl one:
1301069922.956067 sendto(3, "\330\351\t\23\322\7db_bench.tpr"..., 216, 0, NULL, 0) = 216 1301069922.956184 time(NULL) = 1301069922 1301069922.956230 sendto(3, "\330\352\t\23\322\7db_bench.tpr"..., 216, 0, NULL, 0) = 216 1301069922.956343 time(NULL) = 1301069922 1301069922.956389 sendto(3, "\330\353\t\23\322\7db_bench.tpr"..., 216, 0, NULL, 0) = 216 1301069922.956502 time(NULL) = 1301069922 ...
Except the fact that PHP does an extra time() syscall for each loop and that the Perl sendto() syscall send 8 bytes more than PHP one, nothing differs… Looking into perl and PHP modules sources gives use the reason of the 8 extra bytes: our perl is 64 bits compiled, storing all integers as BSON_LONG (64 bits integers), while PHP is probably compiled with SIZEOF_LONG=4, storing all integers as BSON_INT (32 bits integers). As we store 2 integers (idfox and idxxxxxxref values), it adds 2 x 4 bytes for the perl side. Perhaps in the next version of MongoDB perl module (0.43) we will be able to choose how to store integers, see http://jira.mongodb.org/browse/PERL-127.
So next step, the hammer to kill the fly… Let’s try valgrind…
valgrind --tool=callgrind /usr/bin/perl mongo_pain.pl
See you next post…
