11-21-2014
I'm not going to load a database, because the results of the sort will be used just once, and as a practical matter may be passed in a pipe without ever hitting the filesystem. For testing, there's an output file, but just for testing, and to make the results more generally relevant to anyone else who might read this.
My sort times are generally within a factor of 2 of the cost of copying the file to temp and then to the output. So thrashing and computing are not horrible and I'm not going to write a separate sort or any part of it because it will take too long to get it right, and I'm not going to use multiple invocations of sort(1) because the disk I/O will clearly eat any benefits.
I've re-run my timing scripts on the small test file, and some comments I made earlier have to be corrected. The differences between runs are not that alarming after all, and are easily explained by differences in other competing activities on the same machine. My speedups so far are more modest than I thought, but --parallel=4 really does give me 20%, and there's about another 20% available from jiggering parameters.
Running after a fresh boot, I noticed some things that surprised me, though perhaps they should not have. By the time testing is done, the kernel has filled 64GB of memory, mostly with "cached" blocks, and has swapped out a little over 3 MB of memory. I presume it's swapping idle daemons. So these results will not scale up for files large enough to do a complete cache wipe.
I've pretty much determined that the main thing to avoid is getting more than one merge pass on the temporaries. I think it's time to try just a few things with my TB-sized things, because I know those were doing at least 2 extra passes with the default parameters. It took forever. I think the defaults are 4GB buffers (1/8 real memory) and merges of 16 files. The buffers seem to have a lot of overhead, so the temp files are smaller than you might expect. On a 1TB file, that will be roughly 500 2-GB temp files, and 3 levels of merge. The question is: given a choice, is it better to use a bigger buffer, or a wider merge? I'm betting 4GB buffers are too big, but I need to do some testing.
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SORT(1) User Commands SORT(1)
NAME
sort - sort lines of text files
SYNOPSIS
sort [OPTION]... [FILE]...
sort [OPTION]... --files0-from=F
DESCRIPTION
Write sorted concatenation of all FILE(s) to standard output.
With no FILE, or when FILE is -, read standard input.
Mandatory arguments to long options are mandatory for short options too. Ordering options:
-b, --ignore-leading-blanks
ignore leading blanks
-d, --dictionary-order
consider only blanks and alphanumeric characters
-f, --ignore-case
fold lower case to upper case characters
-g, --general-numeric-sort
compare according to general numerical value
-i, --ignore-nonprinting
consider only printable characters
-M, --month-sort
compare (unknown) < 'JAN' < ... < 'DEC'
-h, --human-numeric-sort
compare human readable numbers (e.g., 2K 1G)
-n, --numeric-sort
compare according to string numerical value
-R, --random-sort
shuffle, but group identical keys. See shuf(1)
--random-source=FILE
get random bytes from FILE
-r, --reverse
reverse the result of comparisons
--sort=WORD
sort according to WORD: general-numeric -g, human-numeric -h, month -M, numeric -n, random -R, version -V
-V, --version-sort
natural sort of (version) numbers within text
Other options:
--batch-size=NMERGE
merge at most NMERGE inputs at once; for more use temp files
-c, --check, --check=diagnose-first
check for sorted input; do not sort
-C, --check=quiet, --check=silent
like -c, but do not report first bad line
--compress-program=PROG
compress temporaries with PROG; decompress them with PROG -d
--debug
annotate the part of the line used to sort, and warn about questionable usage to stderr
--files0-from=F
read input from the files specified by NUL-terminated names in file F; If F is - then read names from standard input
-k, --key=KEYDEF
sort via a key; KEYDEF gives location and type
-m, --merge
merge already sorted files; do not sort
-o, --output=FILE
write result to FILE instead of standard output
-s, --stable
stabilize sort by disabling last-resort comparison
-S, --buffer-size=SIZE
use SIZE for main memory buffer
-t, --field-separator=SEP
use SEP instead of non-blank to blank transition
-T, --temporary-directory=DIR
use DIR for temporaries, not $TMPDIR or /tmp; multiple options specify multiple directories
--parallel=N
change the number of sorts run concurrently to N
-u, --unique
with -c, check for strict ordering; without -c, output only the first of an equal run
-z, --zero-terminated
line delimiter is NUL, not newline
--help display this help and exit
--version
output version information and exit
KEYDEF is F[.C][OPTS][,F[.C][OPTS]] for start and stop position, where F is a field number and C a character position in the field; both
are origin 1, and the stop position defaults to the line's end. If neither -t nor -b is in effect, characters in a field are counted from
the beginning of the preceding whitespace. OPTS is one or more single-letter ordering options [bdfgiMhnRrV], which override global order-
ing options for that key. If no key is given, use the entire line as the key. Use --debug to diagnose incorrect key usage.
SIZE may be followed by the following multiplicative suffixes: % 1% of memory, b 1, K 1024 (default), and so on for M, G, T, P, E, Z, Y.
*** WARNING *** The locale specified by the environment affects sort order. Set LC_ALL=C to get the traditional sort order that uses
native byte values.
AUTHOR
Written by Mike Haertel and Paul Eggert.
REPORTING BUGS
GNU coreutils online help: <http://www.gnu.org/software/coreutils/>
Report sort translation bugs to <http://translationproject.org/team/>
COPYRIGHT
Copyright (C) 2017 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>.
This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law.
SEE ALSO
shuf(1), uniq(1)
Full documentation at: <http://www.gnu.org/software/coreutils/sort>
or available locally via: info '(coreutils) sort invocation'
GNU coreutils 8.28 January 2018 SORT(1)