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 EOL patching
$ cat >> $HGRCPATH <<EOF
> [diff]
> git = 1
> EOF
Set up helpers
$ seteol () {
> if [ $1 = "LF" ]; then
> EOL='\n'
> else
> EOL='\r\n'
> fi
> }
$ makerepo () {
> seteol $1
> echo
> echo "# ==== setup $1 repository ===="
> echo '% hg init'
> hg init repo
> cd repo
> cat > .hgeol <<EOF
> [repository]
> native = $1
> [patterns]
> unix.txt = LF
> win.txt = CRLF
> **.txt = native
> EOF
> printf "first\r\nsecond\r\nthird\r\n" > win.txt
> printf "first\nsecond\nthird\n" > unix.txt
> printf "first${EOL}second${EOL}third${EOL}" > native.txt
> hg commit --addremove -m 'checkin'
> cd ..
> }
$ dotest () {
> seteol $1
> echo
> echo "% hg clone repo repo-$1"
> hg clone --noupdate repo repo-$1
> cd repo-$1
> cat > .hg/hgrc <<EOF
> [extensions]
> eol =
> [eol]
> native = $1
> EOF
> hg update
> echo '% native.txt'
> cat native.txt
> echo '% unix.txt'
> cat unix.txt
> echo '% win.txt'
> cat win.txt
> printf "first${EOL}third${EOL}" > native.txt
> printf "first\r\nthird\r\n" > win.txt
> printf "first\nthird\n" > unix.txt
> echo '% hg diff'
> hg diff > p
> cat p
> echo '% hg revert'
> hg revert --all
> echo '% hg import'
> hg import -m 'patch' p
> echo '% native.txt'
> cat native.txt
> echo '% unix.txt'
> cat unix.txt
> echo '% win.txt'
> cat win.txt
> echo '% hg diff -c tip'
> hg diff -c tip
> cd ..
> rm -r repo-$1
> }
Run tests
$ makerepo LF
# ==== setup LF repository ====
% hg init
adding .hgeol
adding native.txt
adding unix.txt
adding win.txt
$ dotest LF
% hg clone repo repo-LF
4 files updated, 0 files merged, 0 files removed, 0 files unresolved
% native.txt
first
second
third
% unix.txt
first
second
third
% win.txt
first\r (esc)
second\r (esc)
third\r (esc)
% hg diff
diff --git a/native.txt b/native.txt
--- a/native.txt
+++ b/native.txt
@@ -1,3 +1,2 @@
first
-second
third
diff --git a/unix.txt b/unix.txt
--- a/unix.txt
+++ b/unix.txt
@@ -1,3 +1,2 @@
first
-second
third
diff --git a/win.txt b/win.txt
--- a/win.txt
+++ b/win.txt
@@ -1,3 +1,2 @@
first\r (esc)
-second\r (esc)
third\r (esc)
% hg revert
reverting native.txt
reverting unix.txt
reverting win.txt
% hg import
applying p
% native.txt
first
third
% unix.txt
first
third
% win.txt
first\r (esc)
third\r (esc)
% hg diff -c tip
diff --git a/native.txt b/native.txt
--- a/native.txt
+++ b/native.txt
@@ -1,3 +1,2 @@
first
-second
third
diff --git a/unix.txt b/unix.txt
--- a/unix.txt
+++ b/unix.txt
@@ -1,3 +1,2 @@
first
-second
third
diff --git a/win.txt b/win.txt
--- a/win.txt
+++ b/win.txt
@@ -1,3 +1,2 @@
first\r (esc)
-second\r (esc)
third\r (esc)
$ dotest CRLF
% hg clone repo repo-CRLF
4 files updated, 0 files merged, 0 files removed, 0 files unresolved
% native.txt
first\r (esc)
second\r (esc)
third\r (esc)
% unix.txt
first
second
third
% win.txt
first\r (esc)
second\r (esc)
third\r (esc)
% hg diff
diff --git a/native.txt b/native.txt
--- a/native.txt
+++ b/native.txt
@@ -1,3 +1,2 @@
first
-second
third
diff --git a/unix.txt b/unix.txt
--- a/unix.txt
+++ b/unix.txt
@@ -1,3 +1,2 @@
first
-second
third
diff --git a/win.txt b/win.txt
--- a/win.txt
+++ b/win.txt
@@ -1,3 +1,2 @@
first\r (esc)
-second\r (esc)
third\r (esc)
% hg revert
reverting native.txt
reverting unix.txt
reverting win.txt
% hg import
applying p
% native.txt
first\r (esc)
third\r (esc)
% unix.txt
first
third
% win.txt
first\r (esc)
third\r (esc)
% hg diff -c tip
diff --git a/native.txt b/native.txt
--- a/native.txt
+++ b/native.txt
@@ -1,3 +1,2 @@
first
-second
third
diff --git a/unix.txt b/unix.txt
--- a/unix.txt
+++ b/unix.txt
@@ -1,3 +1,2 @@
first
-second
third
diff --git a/win.txt b/win.txt
--- a/win.txt
+++ b/win.txt
@@ -1,3 +1,2 @@
first\r (esc)
-second\r (esc)
third\r (esc)
$ rm -r repo
$ makerepo CRLF
# ==== setup CRLF repository ====
% hg init
adding .hgeol
adding native.txt
adding unix.txt
adding win.txt
$ dotest LF
% hg clone repo repo-LF
4 files updated, 0 files merged, 0 files removed, 0 files unresolved
% native.txt
first
second
third
% unix.txt
first
second
third
% win.txt
first\r (esc)
second\r (esc)
third\r (esc)
% hg diff
diff --git a/native.txt b/native.txt
--- a/native.txt
+++ b/native.txt
@@ -1,3 +1,2 @@
first\r (esc)
-second\r (esc)
third\r (esc)
diff --git a/unix.txt b/unix.txt
--- a/unix.txt
+++ b/unix.txt
@@ -1,3 +1,2 @@
first
-second
third
diff --git a/win.txt b/win.txt
--- a/win.txt
+++ b/win.txt
@@ -1,3 +1,2 @@
first\r (esc)
-second\r (esc)
third\r (esc)
% hg revert
reverting native.txt
reverting unix.txt
reverting win.txt
% hg import
applying p
% native.txt
first
third
% unix.txt
first
third
% win.txt
first\r (esc)
third\r (esc)
% hg diff -c tip
diff --git a/native.txt b/native.txt
--- a/native.txt
+++ b/native.txt
@@ -1,3 +1,2 @@
first\r (esc)
-second\r (esc)
third\r (esc)
diff --git a/unix.txt b/unix.txt
--- a/unix.txt
+++ b/unix.txt
@@ -1,3 +1,2 @@
first
-second
third
diff --git a/win.txt b/win.txt
--- a/win.txt
+++ b/win.txt
@@ -1,3 +1,2 @@
first\r (esc)
-second\r (esc)
third\r (esc)
$ dotest CRLF
% hg clone repo repo-CRLF
4 files updated, 0 files merged, 0 files removed, 0 files unresolved
% native.txt
first\r (esc)
second\r (esc)
third\r (esc)
% unix.txt
first
second
third
% win.txt
first\r (esc)
second\r (esc)
third\r (esc)
% hg diff
diff --git a/native.txt b/native.txt
--- a/native.txt
+++ b/native.txt
@@ -1,3 +1,2 @@
first\r (esc)
-second\r (esc)
third\r (esc)
diff --git a/unix.txt b/unix.txt
--- a/unix.txt
+++ b/unix.txt
@@ -1,3 +1,2 @@
first
-second
third
diff --git a/win.txt b/win.txt
--- a/win.txt
+++ b/win.txt
@@ -1,3 +1,2 @@
first\r (esc)
-second\r (esc)
third\r (esc)
% hg revert
reverting native.txt
reverting unix.txt
reverting win.txt
% hg import
applying p
% native.txt
first\r (esc)
third\r (esc)
% unix.txt
first
third
% win.txt
first\r (esc)
third\r (esc)
% hg diff -c tip
diff --git a/native.txt b/native.txt
--- a/native.txt
+++ b/native.txt
@@ -1,3 +1,2 @@
first\r (esc)
-second\r (esc)
third\r (esc)
diff --git a/unix.txt b/unix.txt
--- a/unix.txt
+++ b/unix.txt
@@ -1,3 +1,2 @@
first
-second
third
diff --git a/win.txt b/win.txt
--- a/win.txt
+++ b/win.txt
@@ -1,3 +1,2 @@
first\r (esc)
-second\r (esc)
third\r (esc)
$ rm -r repo