Mercurial > hg
view tests/test-parents.t @ 47802:de2e04fe4897
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
author | Georges Racinet <georges.racinet@octobus.net> |
---|---|
date | Tue, 20 Jul 2021 17:20:19 +0200 |
parents | 50afeeeb7b79 |
children |
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test parents command $ hg init repo $ cd repo no working directory $ hg parents $ echo a > a $ echo b > b $ hg ci -Amab -d '0 0' adding a adding b $ echo a >> a $ hg ci -Ama -d '1 0' $ echo b >> b $ hg ci -Amb -d '2 0' $ echo c > c $ hg ci -Amc -d '3 0' adding c $ hg up -C 1 1 files updated, 0 files merged, 1 files removed, 0 files unresolved $ echo d > c $ hg ci -Amc2 -d '4 0' adding c created new head $ hg up -C 3 2 files updated, 0 files merged, 0 files removed, 0 files unresolved $ hg parents changeset: 3:02d851b7e549 user: test date: Thu Jan 01 00:00:03 1970 +0000 summary: c $ hg parents a changeset: 1:d786049f033a user: test date: Thu Jan 01 00:00:01 1970 +0000 summary: a hg parents c, single revision $ hg parents c changeset: 3:02d851b7e549 user: test date: Thu Jan 01 00:00:03 1970 +0000 summary: c $ hg parents -r 3 c abort: 'c' not found in manifest [10] $ hg parents -r 2 changeset: 1:d786049f033a user: test date: Thu Jan 01 00:00:01 1970 +0000 summary: a $ hg parents -r 2 a changeset: 1:d786049f033a user: test date: Thu Jan 01 00:00:01 1970 +0000 summary: a $ hg parents -r 2 ../a abort: ../a not under root '$TESTTMP/repo' [255] cd dir; hg parents -r 2 ../a $ mkdir dir $ cd dir $ hg parents -r 2 ../a changeset: 1:d786049f033a user: test date: Thu Jan 01 00:00:01 1970 +0000 summary: a $ hg parents -r 2 path:a changeset: 1:d786049f033a user: test date: Thu Jan 01 00:00:01 1970 +0000 summary: a $ cd .. $ hg parents -r 2 glob:a abort: can only specify an explicit filename [10] merge working dir with 2 parents, hg parents c $ HGMERGE=true hg merge merging c 0 files updated, 1 files merged, 0 files removed, 0 files unresolved (branch merge, don't forget to commit) $ hg parents c changeset: 3:02d851b7e549 user: test date: Thu Jan 01 00:00:03 1970 +0000 summary: c changeset: 4:48cee28d4b4e tag: tip parent: 1:d786049f033a user: test date: Thu Jan 01 00:00:04 1970 +0000 summary: c2 merge working dir with 1 parent, hg parents $ hg up -C 2 0 files updated, 0 files merged, 1 files removed, 0 files unresolved $ HGMERGE=true hg merge -r 4 1 files updated, 0 files merged, 0 files removed, 0 files unresolved (branch merge, don't forget to commit) $ hg parents changeset: 2:6cfac479f009 user: test date: Thu Jan 01 00:00:02 1970 +0000 summary: b changeset: 4:48cee28d4b4e tag: tip parent: 1:d786049f033a user: test date: Thu Jan 01 00:00:04 1970 +0000 summary: c2 merge working dir with 1 parent, hg parents c $ hg parents c changeset: 4:48cee28d4b4e tag: tip parent: 1:d786049f033a user: test date: Thu Jan 01 00:00:04 1970 +0000 summary: c2 $ cd ..