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Devel::Arena - Perl extension for inspecting the core's arena structures


  use Devel::Arena 'sv_stats';
  # Get hash ref describing the arenas for SV heads
  $sv_stats = sv_stats;


Inspect the arena structures that perl uses for SV allocation.

HARNESS_PERL_SWITCHES=-MDevel::Arena=write_stats_at_END make test


None by default.

  • sv_stats [DONT_SHARE]

    Returns a hashref giving stats derived from inspecting the SV heads via the arena pointers. Details of the contents of the hash subject to change.

    If the optional argument DONT_SHARE is true then none of the hashes in the returned structure have shared hash keys. This is less efficient, but is needed to calculate the effectiveness of the shared string table.

  • shared_string_table

    Returns a hashref giving the share counts for each entry in the shared string table. The hashref doesn't use shared keys itself, so it doesn't affect the thing that it is measuring.

  • sizes

    Returns a hashref containing sizes of various core perl types, C types, and other size related info (specifically 'hek_key offset')

  • HEK_size STRING

    Calculates the size of the hash key needed to store STRING.

  • shared_string_table_effectiveness

    Calculates the effectiveness of the shared string table. Returns a hashref of stats. Currently this is

              'pv_unshared' => 7185,
              'raw_unshared' => 77264,
              'heks' => 3748,
              'pv_hv' => 77264,
              'hv_unshared' => 70079,
              'raw_shared' => 57675,
              'pvs' => 434,
              'raw' => 1833

    It ignores malloc() overhead, and the possibility that some shared strings aren't used as hash keys or shared hash key scalars.

  • write_stats_at_END

    Not really a function, but if you import write_stats_at_END then Devel::Arena will write out a Storable dump of all stats at END time. The file is written into a file into a file in the current directory named $$ . '.sv_stats'. This allows you to do things such as

        HARNESS_PERL_SWITCHES=-MDevel::Arena=write_stats_at_END make test

    to analyse the resource usage in regression tests.


sv.c in the perl core.


Nicholas Clark, <>


Copyright (C) 2005, 2006 by Nicholas Clark

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself, either Perl version 5.8.6 or, at your option, any later version of Perl 5 you may have available.