NAME

persistent memory gawk - persistent data and functions

SYNOPSIS

    truncate -s size heap.pma
    export GAWK_PERSIST_FILE=heap.pma
    gawk . . .

    truncate -s size heap.pma
    GAWK_PERSIST_FILE=heap.pma gawk . . .

    truncate -s size heap.pma
    alias pm='GAWK_PERSIST_FILE=heap.pma'
    pm gawk . . .                       # succinct

    unset GAWK_PERSIST_FILE   # disable persistence

    export GAWK_PERSIST_FILE=other_heap.pma  # change heap

    rm heap.pma               # delete heap

DESCRIPTION

Gawk 5.2 and later supports a persistent memory feature that can store
script-defined variables and functions in a file for later use. The
feature, called pm-gawk, is described in GAWK: Effective AWK Programming
and in Persistent Memory gawk User Manual.

pm-gawk is activated by passing to gawk the name of an initially empty
(all-zero-bytes) heap file, via the environment variable
GAWK_PERSIST_FILE. pm-gawk retains script-defined variables and
functions in the heap file for use in subsequent gawk invocations.

pm-gawk offers at least two advantages compared with the existing
rwarray extension: it offers constant-time (``O(1) time'') access to
individual elements of persistent associative arrays, and it can store
script-defined functions in addition to variables.

EXAMPLES

Demonstrate persistent variables:

  $ truncate -s 1G heap.pma            # create heap file
      $ export GAWK_PERSIST_FILE=heap.pma  # "ambient" env var
      $ gawk 'BEGIN { print ++i }'
      1
      $ gawk 'BEGIN { print ++i }'
      2
      $ gawk 'BEGIN { print ++i }'
      3

To pass the environment variable on per-command basis:

  $ unset GAWK_PERSIST_FILE
      $ GAWK_PERSIST_FILE=heap.pma gawk 'BEGIN { print ++i }'
      4
      $ GAWK_PERSIST_FILE=heap.pma gawk 'BEGIN { print ++i }'
      5
      $ GAWK_PERSIST_FILE=heap.pma gawk 'BEGIN { print ++i }'
      6

To reduce visual clutter of per-command environment variable passing:

  $ alias pm='GAWK_PERSIST_FILE=heap.pma'
      $ pm gawk 'BEGIN { print ++i }'
      7
      $ pm gawk 'BEGIN { print ++i }'
      8

To refrain from activating persistence:

  $ unset GAWK_PERSIST_FILE
      $ gawk 'BEGIN { print ++i }'
      1
      $ gawk 'BEGIN { print ++i }'
      1

To permanently ``forget'' the contents of the heap file:

  $ rm heap.pma

ENVIRONMENT VARIABLES

GAWK_PERSIST_FILE contains the name of a heap file where script-defined
variables and functions are stored. If this environment variable is not
visible to gawk, the persistence feature is not activated and gawk
behaves in its traditional manner.

VERSION INFORMATION

Persistent memory gawk was first released in gawk 5.2.

AUTHORS

Arnold Robbins, the maintainer of gawk, implemented pm-gawk using a
persistent memory allocator (pma) provided by Terence Kelly. An earlier
proof-of-concept prototype of persistent gawk was developed by Haris
Volos, Zi Fan Tan, and Jianan Li using a fork of the official gawk
sources.

CAVEATS

The GNU/Linux CIFS filesystem is known to cause problems for the
persistent memory allocator. Do not use a backing file on such a
filesystem with pm-gawk.

pm-gawk produces a warning if the current version of gawk doesn't match
the one that was first used with a particular backing storage file.

BUG REPORTS

Follow the procedures in GAWK: Effective AWK Programming and in
Persistent Memory gawk User Manual. For suspected bugs related to
persistence (as opposed to other non-persistence-related gawk bugs)
please also send e-mail to Terence Kelly at one or more of these
addresses: tpkelly@acm.org, tpkelly@eecs.umich.edu, or
tpkelly@cs.princeton.edu.

SEE ALSO

gawk(1), GAWK: Effective AWK Programming, and Persistent Memory gawk
User Manual. The two manuals should be available in the Info subsystem
if Info installed on your system.

See https://web.eecs.umich.edu/~tpkelly/pma/ for the latest source code
and manual.

COPYING PERMISSIONS

Copyright © 2022 Terence Kelly.

Permission is granted to make and distribute verbatim copies of this
manual page provided the copyright notice and this permission notice are
preserved on all copies.

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identical to this one except for the removal of this paragraph (this
paragraph not being relevant to the printed manual page).

Permission is granted to copy and distribute modified versions of this
manual page under the conditions for verbatim copying, provided that the
entire resulting derived work is distributed under the terms of a
permission notice identical to this one.

Permission is granted to copy and distribute translations of this manual
page into another language, under the above conditions for modified
versions, except that this permission notice may be stated in a
translation approved by the Foundation.
