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Top Forums UNIX for Advanced & Expert Users Help optimizing sort of large files Post 302924787 by DGPickett on Wednesday 12th of November 2014 11:23:04 AM
Old 11-12-2014
There is no swap space use with mmap() unless you choose the more exotic options. The basic mmap() swaps in file pages directly to RAM, giving you a way to work huge files with all of RAM as a cache. If you overmap a file, you can write pages. Empty pages can exist, supporting sparse matrices. This is a very powerful door into application use of VM and full exploitation of RAM.

Sorting small into larger in steps allows the problem to periodically expand to the next level of storage: from the caches to the RAM to the disk. The only flaw is that it might be good to merge more than 2 at a time, so when you get to the disk size merges, there is just one or at least fewer. The merge could use some sort of comparison tournament tree to do the merge, sized to fit in L1 cache, where each replacement item needs to be fit into the tree before using the smallest from the tree. Note that each item will take a whole page of RAM, or two, and N-N+2 lines of L1 cache, depending on the cache and item sizes and page/line offsets. Trying to fill L1 cache is fraught with difficulty, as many items may demand the same cache bucket, so it pays to shoot a bit low, like 1/4 - 1/2 L1 cache size.
 

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WRAP-AND-SORT(1)					      General Commands Manual						  WRAP-AND-SORT(1)

NAME
wrap-and-sort - wrap long lines and sort items in Debian packaging files SYNOPSIS
wrap-and-sort [options] DESCRIPTION
wrap-and-sort wraps the package lists in Debian control files. By default the lists will only split into multiple lines if the entries are longer than 80 characters. wrap-and-sort sorts the package lists in Debian control files and all .install files. Beside that wrap-and-sort removes trailing spaces in these files. This script should be run in the root of a Debian package tree. It searches for control, control.in, copyright, copyright.in, install, and *.install in the debian directory. OPTIONS
-h, --help Show this help message and exit. -a, --wrap-always Wrap all package lists in the Debian control file even if the entries are shorter than 80 characters and could fit in one line line. -s, --short-indent Only indent wrapped lines by one space (default is in-line with the field name). -b, --sort-binary-packages Sort binary package paragraphs by name. -k, --keep-first When sorting binary package paragraphs, leave the first one at the top. Unqualified debhelper(7) configuration files are applied to the first package. -n, --no-cleanup Do not remove trailing whitespaces. -d path, --debian-directory=path Location of the debian directory (default: ./debian). -f file, --file=file Wrap and sort only the specified file. You can specify this parameter multiple times. All supported files will be processed if no files are specified. -v, --verbose Print all files that are touched. AUTHORS
wrap-and-sort and this manpage have been written by Benjamin Drung <bdrung@debian.org>. Both are released under the ISC license. DEBIAN
Debian Utilities WRAP-AND-SORT(1)
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