view tests/test-narrow-strip.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

#testcases flat tree
#testcases lfs-on lfs-off

#if lfs-on
  $ cat >> $HGRCPATH <<EOF
  > [extensions]
  > lfs =
  > EOF
#endif

  $ . "$TESTDIR/narrow-library.sh"

#if tree
  $ cat << EOF >> $HGRCPATH
  > [experimental]
  > treemanifest = 1
  > EOF
#endif

create full repo

  $ hg init master
  $ cd master
  $ cat >> .hg/hgrc <<EOF
  > [narrow]
  > serveellipses=True
  > EOF

  $ mkdir inside
  $ echo inside > inside/f1
  $ mkdir outside
  $ echo outside > outside/f1
  $ hg ci -Aqm 'initial'

  $ echo modified > inside/f1
  $ hg ci -qm 'modify inside'

  $ hg co -q 0
  $ echo modified > outside/f1
  $ hg ci -qm 'modify outside'

  $ echo modified again >> outside/f1
  $ hg ci -qm 'modify outside again'

  $ cd ..

  $ hg clone --narrow ssh://user@dummy/master narrow --include inside
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 3 changesets with 2 changes to 1 files (+1 heads)
  new changesets *:* (glob)
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cd narrow
  $ cat >> $HGRCPATH <<EOF
  > [extensions]
  > strip=
  > EOF

Can strip and recover changesets affecting only files within narrow spec

  $ hg co -r 'desc("modify inside")'
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ rm -f .hg/strip-backup/*-backup.hg
  $ hg strip .
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  saved backup bundle to $TESTTMP/narrow/.hg/strip-backup/*-backup.hg (glob)
  $ hg unbundle .hg/strip-backup/*-backup.hg
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files (+1 heads)
  new changesets * (glob)
  (run 'hg heads' to see heads, 'hg merge' to merge)

Can strip and recover changesets affecting files outside of narrow spec

  $ hg co -r 'desc("modify outside")'
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg log -G -T '{rev} {desc}\n'
  o  2 modify inside
  |
  | @  1 modify outside again
  |/
  o  0 initial
  
  $ hg debugdata -m 1
  inside/f1\x004d6a634d5ba06331a60c29ee0db8412490a54fcd (esc) (flat !)
  outside/f1\x0084ba604d54dee1f13310ce3d4ac2e8a36636691a (esc) (flat !)
  inside\x006a8bc41df94075d501f9740587a0c0e13c170dc5t (esc) (tree !)
  outside\x00255c2627ebdd3c7dcaa6945246f9b9f02bd45a09t (esc) (tree !)

  $ rm -f .hg/strip-backup/*-backup.hg
  $ hg strip .
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
  saved backup bundle to $TESTTMP/narrow/.hg/strip-backup/*-backup.hg (glob)
  $ hg unbundle .hg/strip-backup/*-backup.hg
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 0 changes to 0 files (+1 heads)
  new changesets * (glob)
  (run 'hg heads' to see heads, 'hg merge' to merge)
  $ hg log -G -T '{rev} {desc}\n'
  o  2 modify outside again
  |
  | o  1 modify inside
  |/
  @  0 initial
  
Check that hash of file outside narrow spec got restored
  $ hg debugdata -m 2
  inside/f1\x004d6a634d5ba06331a60c29ee0db8412490a54fcd (esc) (flat !)
  outside/f1\x0084ba604d54dee1f13310ce3d4ac2e8a36636691a (esc) (flat !)
  inside\x006a8bc41df94075d501f9740587a0c0e13c170dc5t (esc) (tree !)
  outside\x00255c2627ebdd3c7dcaa6945246f9b9f02bd45a09t (esc) (tree !)

Also verify we can apply the bundle with 'hg pull':
  $ hg co -r 'desc("modify inside")'
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ rm .hg/strip-backup/*-backup.hg
  $ hg strip .
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  saved backup bundle to $TESTTMP/narrow/.hg/strip-backup/*-backup.hg (glob)
#if repobundlerepo
  $ hg pull .hg/strip-backup/*-backup.hg
  pulling from .hg/strip-backup/*-backup.hg (glob)
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files (+1 heads)
  new changesets * (glob)
  (run 'hg heads' to see heads, 'hg merge' to merge)

  $ rm .hg/strip-backup/*-backup.hg
  $ hg strip 0
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
  saved backup bundle to $TESTTMP/narrow/.hg/strip-backup/*-backup.hg (glob)

  $ hg incoming .hg/strip-backup/*-backup.hg
  comparing with .hg/strip-backup/*-backup.hg (glob)
  changeset:   0:* (glob)
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     initial
  
  changeset:   1:9e48d953700d (flat !)
  changeset:   1:3888164bccf0 (tree !)
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     modify outside again
  
  changeset:   2:f505d5e96aa8 (flat !)
  changeset:   2:40b66f95a209 (tree !)
  tag:         tip
  parent:      0:a99f4d53924d (flat !)
  parent:      0:c2a5fabcca3c (tree !)
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     modify inside
  
  $ hg pull .hg/strip-backup/*-backup.hg
  pulling from .hg/strip-backup/*-backup.hg (glob)
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 3 changesets with 2 changes to 1 files (+1 heads)
  new changesets *:* (glob)
  (run 'hg heads' to see heads, 'hg merge' to merge)
#endif