Re^3: Memory Efficient XML Parser

I *do* think that something is wrong with XML in terms of resources. Consider the XML and Storable files generated by this script (note that you should lower the number of records if you are short on RAM as the following tests will take near 1GB of memory or so):

use constant RECS => 1000000;
{
    open my $fh, ">/tmp/bla.xml" or die;
    select $fh;
    print "<addresses>\n";
    for (1..RECS) {
    print <<EOF;
  <address>
     <name>John Smith</name>
     <city>London</city>
  </address>
EOF
    }
    print "</addresses>\n";
}

{
    require Storable;
    my @addresses;
    for (1..RECS) {
    push @addresses, { name => "John Smith", city => "London" };
    }
    Storable::nstore(\@addresses, "/tmp/bla.st");
}
[download]

Two mostly equivalent data sources. Now the two benchmarks (I am using tcsh's time command here, showing system, user, elapsed time and maximum memory):

$ ( set time = ( 0 "%U+%S %E %MK" ) ; time perl -MStorable -e 'retriev
+e "/tmp/bla.st"' )
1.980+0.384 0:02.41 193974K
$ ( set time = ( 0 "%U+%S %E %MK" ) ; time perl -MXML::LibXML -e 'XML:
+:LibXML->new->parse_file("/tmp/bla.xml")->documentElement' )
6.037+1.876 0:08.15 643952K
[download]

So naive parsing of XML is much worse in both memory allocation and CPU time than loading the same Storable file. I guess that most other fast serializers like YAML::Syck or JSON::XS will give similar results.

Comment on Re^3: Memory Efficient XML Parser Select or Download Code

Replies are listed 'Best First'.

Re^4: Memory Efficient XML Parser
by Jenda (Abbot) on Dec 14, 2007 at 00:34 UTC

The data structure built by XML::LibXML is much bigger because it contains much more data. Most of that of no use whatsoever, but still present. It remembers whether the name or city was first, how much whitespace there was around them, that the John Smith and London was the content instead of an attribute etc. Please reread what I said ... you do NOT have to build such a structure. And even if you do build a structure first you can build a specialized (containing only what you need and in a convenient format) data structure. In this particular case this would build a structure equivalent to the one created by Storable using XML::Rules:

use XML::Rules;
my $parser = XML::Rules->new(
    stripspaces => 3,
    rules => [
        _default => 'content',
        address => 'no content array',
        addresses => 'pass no content',
    ]
);

my $data = $parser->parse($XML);

use Data::Dumper;
print Dumper($data->{address});
[download]

Unlike Storable you can process the XML in chunks:

my $parser = XML::Rules->new(
    stripspaces => 3,
    rules => [
        _default => 'content',
        address => sub {print "$_[1]->{name} for $_[1]->{city}\n"; ret
+urn},
        addresses => '',
    ]
);

$parser->parse($XML);
[download]

Of course if you need to store something and the read it completely both using a Perl script then Storable is a better solution, but if you need to exchange data with other systems, XML is most likely the way to go. Whether you waste memory and CPU while processing it or not is up to you.

Jenda
Support Denmark!
Defend the free world!

[reply]
[d/l]
[select]

Re^5: Memory Efficient XML Parser

by eserte (Deacon) on Dec 14, 2007 at 20:57 UTC

Unlike Storable you can process the XML in chunks

[reply]