Request for feature, sort

[David Mathog]

Greetings,

I would like to request a "pre-sorted" (p?) modifier for keys.  I 
frequently sort very large files with one or two of the sort keys 
already in the correct order as a consequence of how those files were 
generated.  Sort currently has no way of accepting this information so 
that

  sort -k 1,1n -k 2,2 -k 3,3 <infile >outfile

pulls the entire file into a buffer and sorts it.  That is slow, takes 
up a lot of memory, and is mostly a waste of CPU cycles.  The suggested 
syntax of:

  sort -k 1,1np -k 2,2p -k 3,3 <infile >outfile

would only sort those small groups of lines where indicated presorted 
keys are all the same.  In typical usage cases the majority of such 
groups have only 1 or a small number of members.  The single line groups 
need not be sorted at all, just emitted, and the other groups would sort 
quickly.  Memory requirements would typically be greatly reduced as well 
- a 100M line file might have a maximum group size of only 10.

This was discussed previously in this thread:

https://superuser.com/questions/1297157/optimally-sort-a-dataset-of-n-keys-when-first-key-is-already-ordered

where external methods to chop up the input and spoon feed it to 
multiple runs of sort are shown.  None of these are going to be as fast 
as it would be if sort itself handled this.

Of course if the input data is not in the expected order that would be 
detected and a fatal error would occur, with the program exiting with an 
error status.  A partial output file may be created in that case.  If 
that partial file would be a problem the issue can be avoided by running 
sort with its (existing) "check" option using only the pre-sorted keys.

Thank you,

David Mathog
address@hidden
Manager, Sequence Analysis Facility, Biology Division, Caltech