view tests/test-bookmarks-merge.t @ 47010:76ae43d5b1db stable

repoview: fix memory leak of filtered repo classes

The leak occurs in long-running server processes with
extensions, and is measured at 110kB per request.

Before this change, the contents of the `_filteredrepotypes`
cache are not properly garbage collected, despite it begin
a `WeakKeyDictionary`.

Extensions have a tendency to generate a new repository class
for each `localrepo` instantiation. Server processes based
on `hgwebdir_mod` will instantiate a new `localrepo` for each
HTTP request that involves a repository.

As a result, with a testing process that repeatedly opens a
repository with several extensions activated
(`topic` notably among them), we see a steady increase in
resident memory of 110kB per repository instantiation before this
change. This is also true, if we call `gc.collect()` at each
instantiation, like `hgwebdir_mod` does, or not.

The cause of the leak is that the *values* aren't weak references.
This change uses `weakref.ref` for the values, and this makes
in our measurements the resident size increase drop to 5kB per
repository instantiation, with no explicit call of `gc.collect()`
at all.
There is currently no reason to believe that this remaining leak
of 5kB is related to or even due to Mercurial core.

We've also seen evidence that `ui.ui` instances weren't properly
garbage collected before the change (with the change, they are).
This could explain why the figures are relatively high.

In theory, the collection of weak references could lead to
much more misses in the cache, so we measured the impact on
the original case that was motivation for introducing that cache
in 7e89bd0cfb86 (see also issue5043): `hg convert` of the
mozilla-central repository. The bad news here is that there is a
major memory leak there, both with and without the present changeset.
There were no more cache misses, and we could see no
more memory leak with this change: the resident size after importing
roughly 100000 changesets was at 12.4GB before, and 12.5GB after.
The small increase is mentioned for completeness only, and we
believe that it should be ignored, at least as long as the main
leak isn't fixed. At less than 1% of the main leak, even finding out
whether it is merely noise would be wasteful.

Original context where this was spotted and first mitigated:
  https://foss.heptapod.net/heptapod/heptapod/-/issues/466

The leak reduction was also obtained in Heptapod inner HTTP server,
which amounts to the same as `hgwebdir_mod` for these questions.

The measurements done with Python 3.9, similar figures seen with 3.8.
More work on our side would be needed to give measurements with 2.7,
because of testing server process does not support it.

# init

  $ hg init
  $ echo a > a
  $ hg add a
  $ hg commit -m'a'
  $ echo b > b
  $ hg add b
  $ hg commit -m'b'
  $ hg up -C 0
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ echo c > c
  $ hg add c
  $ hg commit -m'c'
  created new head

# test merging of diverged bookmarks
  $ hg bookmark -r 1 "c@diverge"
  $ hg bookmark -r 1 b
  $ hg bookmark c
  $ hg bookmarks
     b                         1:d2ae7f538514
   * c                         2:d36c0562f908
     c@diverge                 1:d2ae7f538514
  $ hg merge "c@diverge"
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ hg commit -m'merge'
  $ hg bookmarks
     b                         1:d2ae7f538514
   * c                         3:b8f96cf4688b

  $ hg up -C 3
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (leaving bookmark c)
  $ echo d > d
  $ hg add d
  $ hg commit -m'd'

  $ hg up -C 3
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ echo e > e
  $ hg add e
  $ hg commit -m'e'
  created new head
  $ hg up -C 5
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg bookmark e
  $ hg bookmarks
     b                         1:d2ae7f538514
     c                         3:b8f96cf4688b
   * e                         5:26bee9c5bcf3

# the picked side is bookmarked

  $ hg up -C 4
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  (leaving bookmark e)
  $ hg merge
  abort: heads are bookmarked - please merge with an explicit rev
  (run 'hg heads' to see all heads, specify rev with -r)
  [255]

# our revision is bookmarked

  $ hg up -C e
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  (activating bookmark e)
  $ hg merge
  abort: no matching bookmark to merge - please merge with an explicit rev or bookmark
  (run 'hg heads' to see all heads, specify rev with -r)
  [255]

# merge bookmark heads

  $ hg up -C 4
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  (leaving bookmark e)
  $ echo f > f
  $ hg commit -Am "f"
  adding f
  $ hg bookmarks -r 4 "e@diverged"
  $ hg up -q -C "e@diverged"
  $ hg merge
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ hg parents
  changeset:   4:a0546fcfe0fb
  bookmark:    e@diverged
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     d
  
  changeset:   5:26bee9c5bcf3
  bookmark:    e
  parent:      3:b8f96cf4688b
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     e
  
  $ hg up -C e
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  (activating bookmark e)
  $ hg bookmarks
     b                         1:d2ae7f538514
     c                         3:b8f96cf4688b
   * e                         5:26bee9c5bcf3
     e@diverged                4:a0546fcfe0fb
  $ hg merge
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ hg commit -m'merge'
  $ hg bookmarks
     b                         1:d2ae7f538514
     c                         3:b8f96cf4688b
   * e                         7:ca784329f0ba

# test warning when all heads are inactive bookmarks

  $ hg up -C 6
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  (leaving bookmark e)
  $ echo g > g
  $ hg commit -Am 'g'
  adding g
  $ hg bookmark -i g
  $ hg bookmarks
     b                         1:d2ae7f538514
     c                         3:b8f96cf4688b
     e                         7:ca784329f0ba
     g                         8:04dd21731d95
  $ hg heads
  changeset:   8:04dd21731d95
  bookmark:    g
  tag:         tip
  parent:      6:be381d1126a0
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     g
  
  changeset:   7:ca784329f0ba
  bookmark:    e
  parent:      5:26bee9c5bcf3
  parent:      4:a0546fcfe0fb
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     merge
  
  $ hg merge
  abort: heads are bookmarked - please merge with an explicit rev
  (run 'hg heads' to see all heads, specify rev with -r)
  [255]