Sort large file


 
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# 1  
Sort large file

I was wondering how sort works.

Does file size and time to sort increase geometrically?

I have a 5.3 billion line file I'd like to use with sort -u I'm wondering if that'll take forever because of a geometric expansion?

If it takes 100 hours that's fine but not 100 days.

Thanks so much.
# 2  
I've worked with very large files before but not quite that large. Given several million lines, I found I could reduce the overall time by splitting the file into smaller units using grep, sort and save each unit, then combine the results.

For example, given a file of cksum output which will always begin with a numeric check sum,

Code:
#!/bin/ksh

    I=0
    while [ $I -lt 10 ]
    do
        grep "^$I" file | sort -u > $I.sort
        (( I += 1 ))
    done

    cat ?.sort > file.sorted

This could, of course, be expanded to include any characters replacing the while loop with a for loop.
# 3  
If the file is somewhat redundant and the key is not too huge try awk. Let's say the first two words of the record make the key:
Code:
awk '!arr[$1 $2]++' hugefile > uniquefile

This reads thru the file once, no sorting. Obviously there has to be enough disk space for the outputfile. It uses associative arrays - hash tables is another name.
 

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