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Subject: Re: [Bug 1858467] Re: dbExpand.pl outputs records in non-deterministic order
From: Ben Franksen via Core-talk <core-talk@aps.anl.gov>
To: core-talk@aps.anl.gov
Date: Tue, 07 Jan 2020 13:16:11 -0000
Am 06.01.20 um 20:45 schrieb Andrew Johnson:
> The suggested solution makes the result deterministic but still changes
> the record order. Would it be preferable to keep a list of the records
> in the order in which they were parsed? That wouldn't be hard to do if
> desirable.

An option that tells dbExpand.pl to keep the records in their original
order may be useful for some applications.

However, given that the standard purpose of dbExpand.pl is to create a
"normalized" version of the input db file via the DB_OPT flag (including
re-formatting and removing comments), additionally imposing an order
seems the more useful default behavior.BTW, this is also what the
predecessor dbst did (though with a different order: first by record
type, then by name, IIRC).

There also remains the question of whether to make the other output
commands deterministic, too.

> NB: The sense of the diff above is reversed, '-' lines normally show the
> existing code and '+' lines the new.

Sorry, I mixed up the order of commits in the git diff command.

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https://bugs.launchpad.net/bugs/1858467

Title:
  dbExpand.pl outputs records in non-deterministic order

Status in EPICS Base:
  Triaged
Status in EPICS Base 7.0 series:
  Triaged

Bug description:
  This concerns only the 7.0 branch since in 3.15 there is no
  dbExpand.pl.

  The observed non-determinism makes it hard to compare (diff) generated
  db files if DB_OPT has been set in a Makefile.

  The solution is simple, at the cost of making the procedure slightly
  less efficient:

  diff --git a/modules/database/src/tools/DBD/Output.pm b/modules/database/src/tools/DBD/Output.pm
  index 869b485..55051df 100644
  --- a/modules/database/src/tools/DBD/Output.pm
  +++ b/modules/database/src/tools/DBD/Output.pm
  @@ -118,8 +118,7 @@ sub OutputBreaktables {
   
   sub OutputRecords {
       my ($out, $records) = @_;
  -    foreach my $name (sort(keys %$records)) {
  -        my $rec = $records->{$name};
  +    while (my ($name, $rec) = each %{$records}) {
           next if $name ne $rec->name; # Alias
           printf $out "record(%s, \"%s\") {\n", $rec->recordtype->name, $name;
           printf $out "    alias(\"%s\")\n", $_

  Note: other output routines inside this module are similarly non-
  deterministic in their output, but they are not used by dbExpand.pl.

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References:
[Bug 1858467] [NEW] dbExpand.pl outputs records in non-deterministic order Ben Franksen via Core-talk

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