hgwebdir: avoid systematic full garbage collection
Forcing a systematic full garbage collection upon each request
can serioulsy harm performance. This is reported as
https://bz.mercurial-scm.org/show_bug.cgi?id=6075
With this change we're performing the full collection according
to a new setting, `experimental.web.full-garbage-collection-rate`.
The default value is 1, which doesn't change the behavior and will
allow us to test on real use cases. If the value is 0, no full garbage
collection occurs.
Regardless of the value of the setting, a partial garbage collection
still occurs upon each request (not attempting to collect objects from
the oldest generation). This should be enough to take care of
reference cycles that have been created by the last request
(assessment of this requires changing the setting, not to be 1).
In my experience chasing memory leaks in Mercurial servers,
the full collection never reclaimed any memory, but this is with
Python 3 and biased towards small repositories.
On the other hand, as explained in the Python developer docs [1],
frequent full collections are very harmful in terms of performance if
lots of objects survive the collection, and hence stay in the
oldest generation. Note that `gc.collect()` is indeed trying to
collect the oldest generation [2]. This happens usually in two cases:
- unwanted lingering objects (i.e., an actual memory leak that
the GC cannot do anything about). Sadly, we have lots of those
these days.
- desireable long-term objects, typically in caches (not inner caches
carried by repositories, which should be collected with them). This
is a subject of interest for the Heptapod project.
In short, the flat rate that this change still permits is
probably a bad idea in most cases, and the default value can
be tweaked later on (or even be set to 0) according to experiments
in the wild.
The test is inspired from test-hgwebdir-paths.py
[1] https://devguide.python.org/garbage_collector/#collecting-the-oldest-generation
[2] https://docs.python.org/3/library/gc.html#gc.collect
Differential Revision: https://phab.mercurial-scm.org/D11204
Test the 'check-commit' script
==============================
A fine patch:
$ cat > patch-with-long-header.diff << EOF
> # HG changeset patch
> # User timeless <timeless@mozdev.org>
> # Date 1448911706 0
> # Mon Nov 30 19:28:26 2015 +0000
> # Node ID c41cb6d2b7dbd62b1033727f8606b8c09fc4aa88
> # Parent 42aa0e570eaa364a622bc4443b0bcb79b1100a58
> # ClownJoke This is a veryly long header that should not be warned about because its not the description
> bundle2: use Oxford comma (issue123) (BC)
>
> diff --git a/hgext/transplant.py b/hgext/transplant.py
> --- a/hgext/transplant.py
> +++ b/hgext/transplant.py
> @@ -599,7 +599,7 @@
> return
> if not (opts.get('source') or revs or
> opts.get('merge') or opts.get('branch')):
> - raise error.Abort(_('no source URL, branch revision or revision '
> + raise error.Abort(_('no source URL, branch revision, or revision '
> 'list provided'))
> if opts.get('all'):
>
> + def blahblah(x):
> + pass
> EOF
$ cat patch-with-long-header.diff | $TESTDIR/../contrib/check-commit
This would normally be against the rules, but it's okay because that's
what tagging and signing looks like:
$ cat > creates-a-tag.diff << EOF
> # HG changeset patch
> # User Augie Fackler <raf@durin42.com>
> # Date 1484787778 18000
> # Wed Jan 18 20:02:58 2017 -0500
> # Branch stable
> # Node ID c177635e4acf52923bc3aa9f72a5b1ad1197b173
> # Parent a1dd2c0c479e0550040542e392e87bc91262517e
> Added tag 4.1-rc for changeset a1dd2c0c479e
>
> diff --git a/.hgtags b/.hgtags
> --- a/.hgtags
> +++ b/.hgtags
> @@ -150,3 +150,4 @@ 438173c415874f6ac653efc1099dec9c9150e90f
> eab27446995210c334c3d06f1a659e3b9b5da769 4.0
> b3b1ae98f6a0e14c1e1ba806a6c18e193b6dae5c 4.0.1
> e69874dc1f4e142746ff3df91e678a09c6fc208c 4.0.2
> +a1dd2c0c479e0550040542e392e87bc91262517e 4.1-rc
> EOF
$ $TESTDIR/../contrib/check-commit < creates-a-tag.diff
A patch with lots of errors:
$ cat > patch-with-long-header.diff << EOF
> # HG changeset patch
> # User timeless
> # Date 1448911706 0
> # Mon Nov 30 19:28:26 2015 +0000
> # Node ID c41cb6d2b7dbd62b1033727f8606b8c09fc4aa88
> # Parent 42aa0e570eaa364a622bc4443b0bcb79b1100a58
> # ClownJoke This is a veryly long header that should not be warned about because its not the description
> transplant/foo: this summary is way too long use Oxford comma (bc) (bug123) (issue 244)
>
> diff --git a/hgext/transplant.py b/hgext/transplant.py
> --- a/hgext/transplant.py
> +++ b/hgext/transplant.py
> @@ -599,7 +599,7 @@
> return
> if not (opts.get('source') or revs or
> opts.get('merge') or opts.get('branch')):
> - raise error.Abort(_('no source URL, branch revision or revision '
> + raise error.Abort(_('no source URL, branch revision, or revision '
> 'list provided'))
> if opts.get('all'):
> EOF
$ cat patch-with-long-header.diff | $TESTDIR/../contrib/check-commit
1: username is not an email address
# User timeless
7: summary keyword should be most user-relevant one-word command or topic
transplant/foo: this summary is way too long use Oxford comma (bc) (bug123) (issue 244)
7: (BC) needs to be uppercase
transplant/foo: this summary is way too long use Oxford comma (bc) (bug123) (issue 244)
7: use (issueDDDD) instead of bug
transplant/foo: this summary is way too long use Oxford comma (bc) (bug123) (issue 244)
7: no space allowed between issue and number
transplant/foo: this summary is way too long use Oxford comma (bc) (bug123) (issue 244)
7: summary line too long (limit is 78)
transplant/foo: this summary is way too long use Oxford comma (bc) (bug123) (issue 244)
[1]
A patch with other errors:
$ cat > patch-with-long-header.diff << EOF
> # HG changeset patch
> # User timeless
> # Date 1448911706 0
> # Mon Nov 30 19:28:26 2015 +0000
> # Node ID c41cb6d2b7dbd62b1033727f8606b8c09fc4aa88
> # Parent 42aa0e570eaa364a622bc4443b0bcb79b1100a58
> # ClownJoke This is a veryly long header that should not be warned about because its not the description
> This has no topic and ends with a period.
>
> diff --git a/hgext/transplant.py b/hgext/transplant.py
> --- a/hgext/transplant.py
> +++ b/hgext/transplant.py
> @@ -599,7 +599,7 @@
> if opts.get('all'):
>
>
> +
> + some = otherjunk
> +
> +
> + def blah_blah(x):
> + pass
> +
>
> EOF
$ cat patch-with-long-header.diff | $TESTDIR/../contrib/check-commit
1: username is not an email address
# User timeless
7: don't capitalize summary lines
This has no topic and ends with a period.
7: summary line doesn't start with 'topic: '
This has no topic and ends with a period.
7: don't add trailing period on summary line
This has no topic and ends with a period.
[1]