Oh, well, I meant if you do it in C, Perl has too much overhead for that.

For instance, removing everything not in the hot path for your script: 

while( @fhs ) {
    printf "\r%d\t", scalar( @fhs );
    my $r = int rand @fhs;
    57 unless( length( $bufs[ $r ] ) );
    my $nextRec = substr( $bufs[ $r ], -16, 16, '' );
}

[download]

Perl compiles it into 40 OPs, 35 inside the loop: 

$ perl -MO=Concise,-exec buk.pl
1  <0> enter 
2  <;> nextstate(main 5 buk.pl:1) v:{
3  <{> enterloop(next->z last->13 redo->4) v
10 <#> gv[*fhs] s
11 <1> rv2av[t2] sK/1
12 <|> and(other->4) vK/1
4      <;> nextstate(main 1 buk.pl:2) v
5      <0> pushmark sM
6      <$> const[PV "\r%d\t"] sM
7      <#> gv[*fhs] s
8      <1> rv2av[t5] sK/1
9      <@> prtf vK
a      <;> nextstate(main 1 buk.pl:3) v
b      <#> gv[*fhs] s
c      <1> rv2av[t8] sK/1
d      <1> rand[t9] sK/1
e      <1> int[t10] sK/1
f      <0> padsv[$r:1,3] sRM*/LVINTRO
g      <2> sassign vKS/2
h      <;> nextstate(main 2 buk.pl:4) v:{
i      <#> gv[*bufs] s
j      <1> rv2av sKR/1
k      <0> padsv[$r:1,3] s
l      <2> aelem sK/2
m      <1> length[t12] sKP/1
n      <|> or(other->o) vK/1
o      <;> nextstate(main 2 buk.pl:5) v:{
p      <#> gv[*bufs] s
q      <1> rv2av sKR/1
r      <0> padsv[$r:1,3] s
s      <2> aelem sKM/2
t      <$> const[IV -16] s/FOLD
u      <$> const[IV 16] s
v      <$> const[PV ""] s
w      <@> substr[t16] sK/4
x      <0> padsv[$nextRec:2,3] sRM*/LVINTRO
y      <2> sassign vKS/2
z      <0> unstack v
           goto 10
13 <2> leaveloop vKP/2
14 <@> leave[1 ref] vKP/REFC

[download]
My estimation is that every OP performs between 50 and 100 machine instructions with a good proportion of performance-unfriendly conditional branches. So, roughly, every run of the loop above would require at least 2000 instructions and may be reaching the capacity of the L1 code cache.

On the other hand, an N-way merge in C, on the hot path of the inner loop, requires just to perform a couple of operations plus the key comparisons log2N times. That may sum up to 50 instructions for every loop cycle (=sorted record)!

update: Oops, I forgot to say, in theory!

1 hour to sort 100GB, actually, seems too fast to me. But I think the analysis is sound, and unless I am overlooking some hidden bottleneck, the order or magnitude should be right!

In reply to Re^5: Can you improve upon my algorithm. by salva
in thread Can you improve upon my algorithm. by BrowserUk

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.