view tests/test-strip-cross.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.

test stripping of filelogs where the linkrev doesn't always increase

  $ echo '[extensions]' >> $HGRCPATH
  $ echo 'strip =' >> $HGRCPATH
  $ commit()
  > {
  >     hg up -qC null
  >     count=1
  >     for i in "$@"; do
  >         for f in $i; do
  >             mkdir -p `dirname $f`
  >             echo $count > $f
  >         done
  >         count=`expr $count + 1`
  >     done
  >     hg commit -qAm "$*"
  > }

2 1 0 2 0 1 2

  $ mkdir files
  $ cd files
  $ hg init orig
  $ cd orig
  $ commit '201 210'
  $ commit '102 120' '210'
  $ commit '021'
  $ commit '201' '021 120'
  $ commit '012 021' '102 201' '120 210'
  $ commit '102 120' '012 210' '021 201'
  $ commit '201 210' '021 120' '012 102'
  $ cd ..
  $ hg clone -q -U -r 4 -r 5 -r 6 orig crossed
  $ cd crossed

  $ for i in 012 021 102 120 201 210; do
  >     echo $i
  >     hg debugindex $i
  >     echo
  > done
  012
     rev linkrev nodeid       p1           p2
       0       0 b8e02f643373 000000000000 000000000000
       1       1 5d9299349fc0 000000000000 000000000000
       2       2 2661d26c6496 000000000000 000000000000
  
  021
     rev linkrev nodeid       p1           p2
       0       0 b8e02f643373 000000000000 000000000000
       1       2 5d9299349fc0 000000000000 000000000000
       2       1 2661d26c6496 000000000000 000000000000
  
  102
     rev linkrev nodeid       p1           p2
       0       1 b8e02f643373 000000000000 000000000000
       1       0 5d9299349fc0 000000000000 000000000000
       2       2 2661d26c6496 000000000000 000000000000
  
  120
     rev linkrev nodeid       p1           p2
       0       1 b8e02f643373 000000000000 000000000000
       1       2 5d9299349fc0 000000000000 000000000000
       2       0 2661d26c6496 000000000000 000000000000
  
  201
     rev linkrev nodeid       p1           p2
       0       2 b8e02f643373 000000000000 000000000000
       1       0 5d9299349fc0 000000000000 000000000000
       2       1 2661d26c6496 000000000000 000000000000
  
  210
     rev linkrev nodeid       p1           p2
       0       2 b8e02f643373 000000000000 000000000000
       1       1 5d9299349fc0 000000000000 000000000000
       2       0 2661d26c6496 000000000000 000000000000
  
  $ cd ..
  $ for i in 0 1 2; do
  >     hg clone -q -U --pull crossed $i
  >     echo "% Trying to strip revision $i"
  >     hg --cwd $i strip $i
  >     echo "% Verifying"
  >     hg --cwd $i verify
  >     echo
  > done
  % Trying to strip revision 0
  saved backup bundle to $TESTTMP/files/0/.hg/strip-backup/cbb8c2f0a2e3-239800b9-backup.hg
  % Verifying
  checking changesets
  checking manifests
  crosschecking files in changesets and manifests
  checking files
  checked 2 changesets with 12 changes to 6 files
  
  % Trying to strip revision 1
  saved backup bundle to $TESTTMP/files/1/.hg/strip-backup/124ecc0cbec9-6104543f-backup.hg
  % Verifying
  checking changesets
  checking manifests
  crosschecking files in changesets and manifests
  checking files
  checked 2 changesets with 12 changes to 6 files
  
  % Trying to strip revision 2
  saved backup bundle to $TESTTMP/files/2/.hg/strip-backup/f6439b304a1a-c6505a5f-backup.hg
  % Verifying
  checking changesets
  checking manifests
  crosschecking files in changesets and manifests
  checking files
  checked 2 changesets with 12 changes to 6 files
  
  $ cd ..

Do a similar test where the manifest revlog has unordered linkrevs
  $ mkdir manifests
  $ cd manifests
  $ hg init orig
  $ cd orig
  $ commit 'file'
  $ commit 'other'
  $ commit '' 'other'
  $ HGUSER=another-user; export HGUSER
  $ commit 'file'
  $ commit 'other' 'file'
  $ cd ..
  $ hg clone -q -U -r 1 -r 2 -r 3 -r 4 orig crossed
  $ cd crossed
  $ hg debugindex --manifest
     rev linkrev nodeid       p1           p2
       0       2 6bbc6fee55c2 000000000000 000000000000
       1       0 1c556153fe54 000000000000 000000000000
       2       1 1f76dba919fd 000000000000 000000000000
       3       3 bbee06ad59d5 000000000000 000000000000

  $ cd ..
  $ for i in 2 3; do
  >     hg clone -q -U --pull crossed $i
  >     echo "% Trying to strip revision $i"
  >     hg --cwd $i strip $i
  >     echo "% Verifying"
  >     hg --cwd $i verify
  >     echo
  > done
  % Trying to strip revision 2
  saved backup bundle to $TESTTMP/manifests/2/.hg/strip-backup/f3015ad03c03-4d98bdc2-backup.hg
  % Verifying
  checking changesets
  checking manifests
  crosschecking files in changesets and manifests
  checking files
  checked 3 changesets with 3 changes to 2 files
  
  % Trying to strip revision 3
  saved backup bundle to $TESTTMP/manifests/3/.hg/strip-backup/9632aa303aa4-69192e3f-backup.hg
  % Verifying
  checking changesets
  checking manifests
  crosschecking files in changesets and manifests
  checking files
  checked 3 changesets with 3 changes to 2 files
  
  $ cd ..

Now a similar test for a non-root manifest revlog
  $ cat >> $HGRCPATH <<EOF
  > [experimental]
  > treemanifests = yes
  > EOF
  $ mkdir treemanifests
  $ cd treemanifests
  $ 
  $ hg --config experimental.treemanifest=True init orig
  $ cd orig
  $ commit 'dir/file'
  $ commit 'dir/other'
  $ commit '' 'dir/other'
  $ HGUSER=yet-another-user; export HGUSER
  $ commit 'otherdir dir/file'
  $ commit 'otherdir dir/other' 'otherdir dir/file'
  $ cd ..
  $ hg --config experimental.treemanifest=True clone -q -U -r 1 -r 2 -r 3 -r 4 orig crossed
  $ cd crossed
  $ hg debugindex --dir dir
     rev linkrev nodeid       p1           p2
       0       2 6bbc6fee55c2 000000000000 000000000000
       1       0 1c556153fe54 000000000000 000000000000
       2       1 1f76dba919fd 000000000000 000000000000
       3       3 bbee06ad59d5 000000000000 000000000000

  $ cd ..
  $ for i in 2 3; do
  >     hg --config experimental.treemanifest=True clone -q -U --pull crossed $i
  >     echo "% Trying to strip revision $i"
  >     hg --cwd $i strip $i
  >     echo "% Verifying"
  >     hg --cwd $i verify
  >     echo
  > done
  % Trying to strip revision 2
  saved backup bundle to $TESTTMP/treemanifests/2/.hg/strip-backup/145f5c75f9ac-a105cfbe-backup.hg
  % Verifying
  checking changesets
  checking manifests
  checking directory manifests
  crosschecking files in changesets and manifests
  checking files
  checked 3 changesets with 4 changes to 3 files
  
  % Trying to strip revision 3
  saved backup bundle to $TESTTMP/treemanifests/3/.hg/strip-backup/e4e3de5c3cb2-f4c70376-backup.hg
  % Verifying
  checking changesets
  checking manifests
  checking directory manifests
  crosschecking files in changesets and manifests
  checking files
  checked 3 changesets with 4 changes to 3 files
  
  $ cd ..