Log Message:
miller: update to 5.7.0.

ChangeLog:

Features

    The new remove-empty-columns and skip-trivial-records are
    keystroke-savers for things which would other require DSL
    syntax, as tracked in #274.

Bugfixes

    A bug regarding optional regex-pattern groups was fixed in
    #277.

    As of #294 you can now specify --implicit-csv-header for the
    join-file in mlr join.

    A bug with spaces in XTAB-file values was fixed on #296.

    A bug with missing final newline for XTAB-formatted files
    using MMAP files was fixed on #301.

Documentation

    Look-and-feel at http://johnkerl.org/miller/doc/ is (hopefully)
    improved, including clearer visual indication of which section/page
    you're currently looking at. Note that this change has been
    live for a few weeks, as look-and-feel-related doc-mods from
    post-5.6.2 were backported to http://johnkerl.org/miller/doc/.

    #282 improves DSL-function documentation at
    \ 
http://johnkerl.org/miller/doc/reference-dsl.html#Built-in_functions_for_filter_and_put,_summary

Note

Support for mmap mode has been entirely discontinued. This is an
invisible change and should not affect you at all. For anyone
interested in lower-level details, though, the summary is as follows:

    For an incremental performance gain (perhaps 10-20% run time
    at most, but see below), within the C source code one can use
    the mmap system call to access input files via pointer arithmetic
    rather than malloc-and-memcopy using stdio.

    However mmap is not available when reading from standard
    input -- it cannot be memory-mapped.

    This means all file-format readers are implemented twice
    within the Miller source code.

    While I try to regression-test Miller thoroughly, running
    all canned tests through mmap and stdio mode, I've nonetheless
    found my mmap implementations liable to corner-cases which I
    miss but users find: for example #29, #102, and #296.

    As tracked on #160, various operating systems do not release
    mmapped pages after use as one might intuit, meaning that for
    large files and/or large numbers of files, I've for a long time
    now needed to have Miller opt out of mmap usage for precisely
    those cases which most need the performance gain: see #160,
    #181, and #256.

    Additionally, mmap is not used at all for Windows/MSYS2 so
    there is nothing to lose there.

For these reasons, keeping mmap mode isn't worth the development
overhead.

As of release 5.6.3, the mlr executable will still accept the --mmap
and --no-mmap command-line flags as no-ops, for backward compatibility.

The caveat for you is that for everyday small files, the default
was previously mmap mode and is now stdio (except mlr ... < filename
or ... | mlr ... which have always used stdio). There is the off
chance that this will newly reveal an old, latent bug or two
somewhere.

I've re-run regressions in valgrind mode to aggressively catch any
errors, but, please let me know ASAP via GitHub issue of any
unexpected behavior in 5.7.0.