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
$ echo "[extensions]" >> $HGRCPATH
$ echo "churn=" >> $HGRCPATH
create test repository
$ hg init repo
$ cd repo
$ echo a > a
$ hg ci -Am adda -u user1 -d 6:00
adding a
$ echo b >> a
$ echo b > b
$ hg ci -m changeba -u user2 -d 9:00 a
$ hg ci -Am addb -u user2 -d 9:30
adding b
$ echo c >> a
$ echo c >> b
$ echo c > c
$ hg ci -m changeca -u user3 -d 12:00 a
$ hg ci -m changecb -u user3 -d 12:15 b
$ hg ci -Am addc -u user3 -d 12:30
adding c
$ mkdir -p d/e
$ echo abc > d/e/f1.txt
$ hg ci -Am "add d/e/f1.txt" -u user1 -d 12:45 d/e/f1.txt
$ mkdir -p d/g
$ echo def > d/g/f2.txt
$ hg ci -Am "add d/g/f2.txt" -u user1 -d 13:00 d/g/f2.txt
churn separate directories
$ cd d
$ hg churn e
user1 1 ***************************************************************
churn all
$ hg churn
user1 3 ***************************************************************
user3 3 ***************************************************************
user2 2 ******************************************
churn excluding one dir
$ hg churn -X e
user3 3 ***************************************************************
user1 2 ******************************************
user2 2 ******************************************
churn up to rev 2
$ hg churn -r :2
user2 2 ***************************************************************
user1 1 *******************************
$ cd ..
churn with aliases
$ cat > ../aliases <<EOF
> user1 alias1
> user3 alias3
> not-an-alias
> EOF
churn with .hgchurn
$ mv ../aliases .hgchurn
$ hg churn
skipping malformed alias: not-an-alias
alias1 3 **************************************************************
alias3 3 **************************************************************
user2 2 *****************************************
$ rm .hgchurn
churn with column specifier
$ COLUMNS=40 hg churn
user1 3 ***********************
user3 3 ***********************
user2 2 ***************
churn by hour
$ hg churn -f '%H' -s
06 1 ****************
09 2 *********************************
12 4 ******************************************************************
13 1 ****************
churn with separated added/removed lines
$ hg rm d/g/f2.txt
$ hg ci -Am "removed d/g/f2.txt" -u user1 -d 14:00 d/g/f2.txt
$ hg churn --diffstat
user1 +3/-1 ++++++++++++++++++++++++++++++++++++++++-------------
user3 +3/-0 ++++++++++++++++++++++++++++++++++++++++
user2 +2/-0 +++++++++++++++++++++++++++
churn --diffstat with color
$ hg --config extensions.color= churn --config color.mode=ansi \
> --diffstat --color=always
user1 +3/-1 \x1b[0;32m++++++++++++++++++++++++++++++++++++++++\x1b[0m\x1b[0;31m-------------\x1b[0m (esc)
user3 +3/-0 \x1b[0;32m++++++++++++++++++++++++++++++++++++++++\x1b[0m (esc)
user2 +2/-0 \x1b[0;32m+++++++++++++++++++++++++++\x1b[0m (esc)
changeset number churn
$ hg churn -c
user1 4 ***************************************************************
user3 3 ***********************************************
user2 2 *******************************
$ echo 'with space = no-space' >> ../aliases
$ echo a >> a
$ hg commit -m a -u 'with space' -d 15:00
churn with space in alias
$ hg churn --aliases ../aliases -r tip
no-space 1 ************************************************************
$ cd ..
Issue833: ZeroDivisionError
$ hg init issue-833
$ cd issue-833
$ touch foo
$ hg ci -Am foo
adding foo
this was failing with a ZeroDivisionError
$ hg churn
test 0
$ cd ..
Ignore trailing or leading spaces in emails
$ cd repo
$ touch bar
$ hg ci -Am'bar' -u 'user4 <user4@x.com>'
adding bar
$ touch foo
$ hg ci -Am'foo' -u 'user4 < user4@x.com >'
adding foo
$ hg log -l2 --template '[{author|email}]\n'
[ user4@x.com ]
[user4@x.com]
$ hg churn -c
user1 4 *********************************************************
user3 3 ******************************************
user2 2 ****************************
user4@x.com 2 ****************************
with space 1 **************
Test multibyte sequences in names
$ echo bar >> bar
$ hg --encoding utf-8 ci -m'changed bar' -u 'El Niño <nino@x.com>'
$ hg --encoding utf-8 churn -ct '{author|person}'
user1 4 **********************************************************
user3 3 *******************************************
user2 2 *****************************
user4 2 *****************************
El Ni\xc3\xb1o 1 ************** (esc)
with space 1 **************
Test --template argument, with backwards compatibility
$ hg churn -t '{author|user}'
user1 4 ***************************************************************
user3 3 ***********************************************
user2 2 *******************************
nino 1 ***************
with 1 ***************
0
user4 0
$ hg churn -T '{author|user}'
user1 4 ***************************************************************
user3 3 ***********************************************
user2 2 *******************************
nino 1 ***************
with 1 ***************
0
user4 0
$ hg churn -t 'alltogether'
alltogether 11 *********************************************************
$ hg churn -T 'alltogether'
alltogether 11 *********************************************************
$ cd ..
count lines that look like headings but are not
$ hg init not-headers
$ cd not-headers
$ cat > a <<EOF
> diff
> @@ -195,3 +195,21 @@
> -- a/tests/test-churn.t
> ++ b/tests/test-churn.t
> EOF
$ hg ci -Am adda -u user1
adding a
$ hg churn --diffstat
user1 +4/-0 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
$ hg rm a
$ hg ci -Am removea -u user1
$ hg churn --diffstat
user1 +4/-4 +++++++++++++++++++++++++++---------------------------