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
$ hg init
no bookmarks
$ hg bookmarks
no bookmarks set
set bookmark X
$ hg bookmark X
list bookmarks
$ hg bookmark
* X -1:000000000000
list bookmarks with color
$ hg --config extensions.color= --config color.mode=ansi \
> bookmark --color=always
\x1b[0;32m * \x1b[0m\x1b[0;32mX\x1b[0m\x1b[0;32m -1:000000000000\x1b[0m (esc)
update to bookmark X
$ hg bookmarks
* X -1:000000000000
$ hg update X
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
list bookmarks
$ hg bookmarks
* X -1:000000000000
rename
$ hg bookmark -m X Z
list bookmarks
$ cat .hg/bookmarks.current
Z (no-eol)
$ cat .hg/bookmarks
0000000000000000000000000000000000000000 Z
$ hg bookmarks
* Z -1:000000000000
new bookmarks X and Y, first one made active
$ hg bookmark Y X
list bookmarks
$ hg bookmark
X -1:000000000000
* Y -1:000000000000
Z -1:000000000000
$ hg bookmark -d X
commit
$ echo 'b' > b
$ hg add b
$ hg commit -m'test'
list bookmarks
$ hg bookmark
* Y 0:719295282060
Z -1:000000000000
Verify that switching to Z updates the active bookmark:
$ hg update Z
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
(activating bookmark Z)
$ hg bookmark
Y 0:719295282060
* Z -1:000000000000
Switch back to Y for the remaining tests in this file:
$ hg update Y
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
(activating bookmark Y)
delete bookmarks
$ hg bookmark -d Y
$ hg bookmark -d Z
list bookmarks
$ hg bookmark
no bookmarks set
update to tip
$ hg update tip
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
set bookmark Y using -r . but make sure that the active
bookmark is not activated
$ hg bookmark -r . Y
list bookmarks, Y should not be active
$ hg bookmark
Y 0:719295282060
now, activate Y
$ hg up -q Y
set bookmark Z using -i
$ hg bookmark -r . -i Z
$ hg bookmarks
* Y 0:719295282060
Z 0:719295282060
deactivate active bookmark using -i
$ hg bookmark -i Y
$ hg bookmarks
Y 0:719295282060
Z 0:719295282060
$ hg up -q Y
$ hg bookmark -i
$ hg bookmarks
Y 0:719295282060
Z 0:719295282060
$ hg bookmark -i
no active bookmark
$ hg up -q Y
$ hg bookmarks
* Y 0:719295282060
Z 0:719295282060
deactivate active bookmark while renaming
$ hg bookmark -i -m Y X
$ hg bookmarks
X 0:719295282060
Z 0:719295282060
bare update moves the active bookmark forward and clear the divergent bookmarks
$ echo a > a
$ hg ci -Am1
adding a
$ echo b >> a
$ hg ci -Am2
$ hg bookmark X@1 -r 1
$ hg bookmark X@2 -r 2
$ hg update X
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
(activating bookmark X)
$ hg bookmarks
* X 0:719295282060
X@1 1:cc586d725fbe
X@2 2:49e1c4e84c58
Z 0:719295282060
$ hg update
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
updating bookmark X
$ hg bookmarks
* X 2:49e1c4e84c58
Z 0:719295282060
test deleting .hg/bookmarks.current when explicitly updating
to a revision
$ echo a >> b
$ hg ci -m.
$ hg up -q X
$ test -f .hg/bookmarks.current
try to update to it again to make sure we don't
set and then unset it
$ hg up -q X
$ test -f .hg/bookmarks.current
$ hg up -q 1
$ test -f .hg/bookmarks.current
[1]
when a bookmark is active, hg up -r . is
analogous to hg book -i <active bookmark>
$ hg up -q X
$ hg up -q .
$ test -f .hg/bookmarks.current
[1]
issue 4552 -- simulate a pull moving the active bookmark
$ hg up -q X
$ printf "Z" > .hg/bookmarks.current
$ hg log -T '{activebookmark}\n' -r Z
Z
$ hg log -T '{bookmarks % "{active}\n"}' -r Z
Z
test that updating to closed branch head also advances active bookmark
$ hg commit --close-branch -m "closed"
$ hg update -q ".^1"
$ hg bookmark Y
$ hg bookmarks
X 3:4d6bd4bfb1ae
* Y 3:4d6bd4bfb1ae
Z 0:719295282060
$ hg update
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
updating bookmark Y
$ hg bookmarks
X 3:4d6bd4bfb1ae
* Y 4:8fa964221e8e
Z 0:719295282060
$ hg parents -q
4:8fa964221e8e
Checks command to retrieve active bookmark
------------------------------------------
display how "{activebookmark}" template is unsuitable for the task
$ hg book -T '- {activebookmark}\n'
-
- Y
-
$ hg book -r . W
$ hg book -T '- {activebookmark}\n'
- Y
-
- Y
-
$ hg bookmarks -ql .
Y
$ hg bookmarks --inactive
$ hg bookmarks -ql .
abort: no active bookmark
[255]