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It may be not good to have large hash which takes much memory. Sometimes I met such case with my poor program,I am interested in this topic.

As a result, "keys" seems faster and smaller than "each" on FreeBSD 8.2, perl 5.12.2. This is first time I use GTop, so there may be something wrong with my test script. In such case, let me know about it, please.

this is perl script with GTop and HiRes.

#!/usr/bin/perl
use strict;
use warnings;
use GTop();
use Time::HiRes;

my($gtop,$max,%h,@t);

$gtop=new GTop;
$t[0]=Time::HiRes::time();

printf "###count=$ARGV[1],$ARGV[0]###\n";
p("before");
$max=$ARGV[1];
%h=map { $_ => "test" } (1 .. $max);

p("after hash");

if ($ARGV[0] eq "keys"){
    &with_keys();
} elsif($ARGV[0] eq "each") {
    &with_each();
} else {
    print "else\n";
}

p("after loop");

$t[1]=Time::HiRes::time();
printf "time=%.3f\n", ($t[1]-$t[0]);

exit;
[download]

And shell script to kick this.

perl tmp.pl keys 10000 >  log
perl tmp.pl each 10000 >> log
perl tmp.pl keys 100000 >>  log
perl tmp.pl each 100000 >> log
perl tmp.pl keys 1000000 >> log
perl tmp.pl each 1000000 >> log
perl tmp.pl keys 2000000 >> log
perl tmp.pl each 2000000 >> log
[download]

Result log is as below.

###count=10000,keys###
before: size=10035200,vsize=10035200,resident=5500928,share=5143114,rs
+s=5500928
after hash: size=13180928,vsize=13180928,resident=8306688,share=514311
+4,rss=8306688
after loop: size=13180928,vsize=13180928,resident=8376320,share=514311
+4,rss=8376320
time=0.043
###count=10000,each###
before: size=10035200,vsize=10035200,resident=5541888,share=5143114,rs
+s=5541888
after hash: size=13180928,vsize=13180928,resident=8347648,share=514311
+4,rss=8347648
after loop: size=13180928,vsize=13180928,resident=8417280,share=514311
+4,rss=8417280
time=0.050
###count=100000,keys###
before: size=10035200,vsize=10035200,resident=5541888,share=5143114,rs
+s=5541888
after hash: size=43589632,vsize=43589632,resident=39514112,share=51431
+14,rss=39514112
after loop: size=43589632,vsize=43589632,resident=39514112,share=51431
+14,rss=39514112
time=0.689
###count=100000,each###
before: size=10035200,vsize=10035200,resident=5541888,share=5143114,rs
+s=5541888
after hash: size=43589632,vsize=43589632,resident=39514112,share=51431
+14,rss=39514112
after loop: size=43589632,vsize=43589632,resident=39514112,share=51431
+14,rss=39514112
time=0.799
###count=1000000,keys###
before: size=10035200,vsize=10035200,resident=5545984,share=5143114,rs
+s=5545984
after hash: size=296296448,vsize=296296448,resident=282710016,share=51
+43114,rss=282710016
after loop: size=297345024,vsize=297345024,resident=282718208,share=51
+43114,rss=282718208
time=7.389
###count=1000000,each###
before: size=10035200,vsize=10035200,resident=5545984,share=5143114,rs
+s=5545984
after hash: size=296296448,vsize=296296448,resident=282710016,share=51
+43114,rss=282710016
after loop: size=297345024,vsize=297345024,resident=282718208,share=51
+43114,rss=282718208
time=8.522
###count=2000000,keys###
before: size=10035200,vsize=10035200,resident=5545984,share=5143114,rs
+s=5545984
after hash: size=582557696,vsize=582557696,resident=354185216,share=51
+43114,rss=354185216
after loop: size=583606272,vsize=583606272,resident=360177664,share=51
+43114,rss=360177664
time=103.454
###count=2000000,each###
before: size=10035200,vsize=10035200,resident=5484544,share=5143114,rs
+s=5484544
after hash: size=582557696,vsize=582557696,resident=359972864,share=51
+43114,rss=359972864
after loop: size=583606272,vsize=583606272,resident=352419840,share=51
+43114,rss=352419840
time=268.264
[download]

After keys counts exceed million, it seems iteration needs some extra memory, and memory consumption is same between "keys" and "each". "keys" becomes very fast in 2 million case. But Benchmark shows different result.

#!/usr/bin/perl
use strict;
use warnings;
use Data::Dumper;
use Benchmark qw/cmpthese timethese/;

my($max,%h);
$max=1000000;
%h=map { $_ => "test" } (1 .. $max);
sub with_keys{
    foreach my $k (keys %h){
        #no proc
    }
}
sub with_each{
    while( my($k,$v)=each %h){
        #no proc
    }
}

cmpthese(
    timethese(
        100,
        {
            'with keys'=> &with_keys,
            'with each'=> &with_each,
        }
    )
);
[download]

Output shows these are same.

Benchmark: timing 100 iterations of with each, with keys...
 with each:  0 wallclock secs ( 0.00 usr +  0.00 sys =  0.00 CPU)
            (warning: too few iterations for a reliable count)
 with keys:  0 wallclock secs ( 0.00 usr +  0.00 sys =  0.00 CPU)
            (warning: too few iterations for a reliable count)
                          Rate with each with keys
with each 100000000000000000/s        --        0%
with keys 100000000000000000/s        0%        --
[download]

I left my pc alone while running my test scripts...I believe. Would someone give me insights about these result? I wonder why?

In reply to Re^5: Finding the size of a nested hash in a HoH by remiah
in thread Finding the size of a nested hash in a HoH by Jeri

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