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From: Tomi Ollila <tomi.ollila@iki.fi>
To: David Edmondson <dme@dme.org>, notmuch@notmuchmail.org
Subject: Re: [PATCH v3] emacs: Call "notmuch tag" once when applying tag
	changes to a thread.
In-Reply-To: <1328690169-6991-1-git-send-email-dme@dme.org>
References: <1328632303-31877-1-git-send-email-jani@nikula.org>
	<1328690169-6991-1-git-send-email-dme@dme.org>
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Date: Wed, 08 Feb 2012 11:59:36 +0200
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On Wed,  8 Feb 2012 08:36:09 +0000, David Edmondson <dme@dme.org> wrote:
> Optimize thread tagging by combining all the tagging operations to a
> single "notmuch tag" call.
> 
> For threads in the order of tens or a hundred inbox tagged messages,
> this gives a noticeable speedup. On two different machines, archiving
> a thread of about 50 inbox tagged messages goes down from 10+ seconds
> to about 0.5 seconds.
> 
> The bottleneck is not within emacs; the same behaviour can be observed
> in the CLI. This approach has the added benefit of being more
> reliable: any of the individual tagging operations might face a locked
> database, leading to partial results.
> 
> This introduces a limitation to the number of messages that can be
> archived at the same time (through ARG_MAX limiting the command
> line). While at least on Linux this seems more like a theoretical
> limitation than a real one, it could be avoided by archiving at most a
> few hundred messages at a time.

I did a simple test program:

--8<----8<----8<----8<----8<----8<----8<----8<----8<----8<----8<--
#!/usr/bin/perl

use strict;
use warnings;

die "Usage: $0 <arglen> <# of args>\n" unless @ARGV == 2;

my $arg = 'x' x $ARGV[0];
my @args = ( $arg ) x $ARGV[1];

print "One arg: '$arg'\n";
print 'Number of args: ', scalar @args, "\n";

exec '/bin/true', @args;
--8<----8<----8<----8<----8<----8<----8<----8<----8<----8<----8<--

This program executes /bin/true with given number of args all args
of some length: i.e.

./test_cmdlimit 100 10000 

makes 10000 100 character arguments (total of million characters)
and executes /bin/true with those ten thousand 100-char args.

In one machine where  getconf ARG_MAX  returns 131072
(Debian Lenny ia32)

./test_cmdlimit 200 10000   succeeds
but
./test_cmdlimit 20 100000   gives
Can't exec "/bin/true": Argument list too long at ./test_cmdlimit.pl line 14.

Hmm, actually there:
./test_cmdlimit 19 100000   succeeds and
./test_cmdlimit.pl 209 10000 fails

More with args which lengths are 1 and 2 chars:

./test_cmdlimit.pl 1 1046163 succeeds
./test_cmdlimit.pl 1 1046164 fails

./test_cmdlimit.pl 2 697442 succeeds
./test_cmdlimit.pl 2 697443 fails

1046163 was close to 1048576 (1024 * 1024) --
697442 * 2 is 1394884...

>From these I can make an educated guess that when message id:s
are typically between 30 to 70 characters something like
20 000 messages are safe to be tagged at once in this
test system (./test_cmdlimit.pl 50 40000 succeeds).

> 
> Based on code from Jani Nikula <jani@nikula.org>.

Tomi