view tests/test-narrow-exchange-merges.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.

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

create full repo

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

  $ mkdir inside
  $ echo 1 > inside/f
  $ hg commit -Aqm 'initial inside'

  $ mkdir outside
  $ echo 1 > outside/f
  $ hg commit -Aqm 'initial outside'

  $ echo 2a > outside/f
  $ hg commit -Aqm 'outside 2a'
  $ echo 3 > inside/f
  $ hg commit -Aqm 'inside 3'
  $ echo 4a > outside/f
  $ hg commit -Aqm 'outside 4a'
  $ hg update '.~3'
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved

  $ echo 2b > outside/f
  $ hg commit -Aqm 'outside 2b'
  $ echo 3 > inside/f
  $ hg commit -Aqm 'inside 3'
  $ echo 4b > outside/f
  $ hg commit -Aqm 'outside 4b'
  $ hg update '.~3'
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved

  $ echo 2c > outside/f
  $ hg commit -Aqm 'outside 2c'
  $ echo 3 > inside/f
  $ hg commit -Aqm 'inside 3'
  $ echo 4c > outside/f
  $ hg commit -Aqm 'outside 4c'
  $ hg update '.~3'
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved

  $ echo 2d > outside/f
  $ hg commit -Aqm 'outside 2d'
  $ echo 3 > inside/f
  $ hg commit -Aqm 'inside 3'
  $ echo 4d > outside/f
  $ hg commit -Aqm 'outside 4d'

  $ hg update -r 'desc("outside 4a")'
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg merge -r 'desc("outside 4b")' 2>&1 | egrep -v '(warning:|incomplete!)'
  merging outside/f
  0 files updated, 0 files merged, 0 files removed, 1 files unresolved
  use 'hg resolve' to retry unresolved file merges or 'hg merge --abort' to abandon
  $ echo 5 > outside/f
  $ rm outside/f.orig
  $ hg resolve --mark outside/f
  (no more unresolved files)
  $ hg commit -m 'merge a/b 5'
  $ echo 6 > outside/f
  $ hg commit -Aqm 'outside 6'

  $ hg merge -r 'desc("outside 4c")' 2>&1 | egrep -v '(warning:|incomplete!)'
  merging outside/f
  0 files updated, 0 files merged, 0 files removed, 1 files unresolved
  use 'hg resolve' to retry unresolved file merges or 'hg merge --abort' to abandon
  $ echo 7 > outside/f
  $ rm outside/f.orig
  $ hg resolve --mark outside/f
  (no more unresolved files)
  $ hg commit -Aqm 'merge a/b/c 7'
  $ echo 8 > outside/f
  $ hg commit -Aqm 'outside 8'

  $ hg merge -r 'desc("outside 4d")' 2>&1 | egrep -v '(warning:|incomplete!)'
  merging outside/f
  0 files updated, 0 files merged, 0 files removed, 1 files unresolved
  use 'hg resolve' to retry unresolved file merges or 'hg merge --abort' to abandon
  $ echo 9 > outside/f
  $ rm outside/f.orig
  $ hg resolve --mark outside/f
  (no more unresolved files)
  $ hg commit -Aqm 'merge a/b/c/d 9'
  $ echo 10 > outside/f
  $ hg commit -Aqm 'outside 10'

  $ echo 11 > inside/f
  $ hg commit -Aqm 'inside 11'
  $ echo 12 > outside/f
  $ hg commit -Aqm 'outside 12'

  $ hg log -G -T '{rev} {node|short} {desc}\n'
  @  21 8d874d57adea outside 12
  |
  o  20 7ef88b4dd4fa inside 11
  |
  o  19 2a20009de83e outside 10
  |
  o    18 3ac1f5779de3 merge a/b/c/d 9
  |\
  | o  17 38a9c2f7e546 outside 8
  | |
  | o    16 094aa62fc898 merge a/b/c 7
  | |\
  | | o  15 f29d083d32e4 outside 6
  | | |
  | | o    14 2dc11382541d merge a/b 5
  | | |\
  o | | |  13 27d07ef97221 outside 4d
  | | | |
  o | | |  12 465567bdfb2d inside 3
  | | | |
  o | | |  11 d1c61993ec83 outside 2d
  | | | |
  | o | |  10 56859a8e33b9 outside 4c
  | | | |
  | o | |  9 bb96a08b062a inside 3
  | | | |
  | o | |  8 b844052e7b3b outside 2c
  |/ / /
  | | o  7 9db2d8fcc2a6 outside 4b
  | | |
  | | o  6 6418167787a6 inside 3
  | | |
  +---o  5 77344f344d83 outside 2b
  | |
  | o  4 9cadde08dc9f outside 4a
  | |
  | o  3 019ef06f125b inside 3
  | |
  | o  2 75e40c075a19 outside 2a
  |/
  o  1 906d6c682641 initial outside
  |
  o  0 9f8e82b51004 initial inside
  

Now narrow clone this and get a hopefully correct graph

  $ cd ..
  $ hg clone --narrow ssh://user@dummy/master narrow --include inside
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 14 changesets with 3 changes to 1 files
  new changesets *:* (glob)
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cd narrow

To make updating the tests easier, we print the emitted nodes
sorted. This makes it easier to identify when the same node structure
has been emitted, just in a different order.

  $ hg log -T '{if(ellipsis,"...")}{node|short} {p1node|short} {p2node|short} {desc}\n' | sort
  ...094aa62fc898 6418167787a6 bb96a08b062a merge a/b/c 7
  ...2a20009de83e 019ef06f125b 3ac1f5779de3 outside 10
  ...3ac1f5779de3 465567bdfb2d 094aa62fc898 merge a/b/c/d 9
  ...75e40c075a19 9f8e82b51004 000000000000 outside 2a
  ...77344f344d83 9f8e82b51004 000000000000 outside 2b
  ...8d874d57adea 7ef88b4dd4fa 000000000000 outside 12
  ...b844052e7b3b 9f8e82b51004 000000000000 outside 2c
  ...d1c61993ec83 9f8e82b51004 000000000000 outside 2d
  019ef06f125b 75e40c075a19 000000000000 inside 3
  465567bdfb2d d1c61993ec83 000000000000 inside 3
  6418167787a6 77344f344d83 000000000000 inside 3
  7ef88b4dd4fa 2a20009de83e 000000000000 inside 11
  9f8e82b51004 000000000000 000000000000 initial inside
  bb96a08b062a b844052e7b3b 000000000000 inside 3

But seeing the graph is also nice:
  $ hg log -G -T '{if(ellipsis,"...")}{node|short} {desc}\n'
  @  ...8d874d57adea outside 12
  |
  o  7ef88b4dd4fa inside 11
  |
  o    ...2a20009de83e outside 10
  |\
  | o    ...3ac1f5779de3 merge a/b/c/d 9
  | |\
  | | o    ...094aa62fc898 merge a/b/c 7
  | | |\
  | o | |  465567bdfb2d inside 3
  | | | |
  | o | |  ...d1c61993ec83 outside 2d
  | | | |
  | | | o  bb96a08b062a inside 3
  | | | |
  | +---o  ...b844052e7b3b outside 2c
  | | |
  | | o  6418167787a6 inside 3
  | | |
  | | o  ...77344f344d83 outside 2b
  | |/
  o |  019ef06f125b inside 3
  | |
  o |  ...75e40c075a19 outside 2a
  |/
  o  9f8e82b51004 initial inside