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
============================================
Testing obsolescence markers push: Cases C.1
============================================
Mercurial pushes obsolescences markers relevant to the "pushed-set", the set of
all changesets that requested to be "in sync" after the push (even if they are
already on both side).
This test belongs to a series of tests checking such set is properly computed
and applied. This does not tests "obsmarkers" discovery capabilities.
Category C: advanced case
TestCase 1: Multiple pruned changeset atop each other
Variants:
# a: explicite push
# b: bare push
C.1 Multiple pruned changeset atop each other
=============================================
.. {{{
.. ⊗ B
.. |
.. ⊗ A
.. |
.. ● O
.. }}}
..
.. Marker exist from:
..
.. * A (prune)
.. * B (prune)
..
.. Commands run:
..
.. * hg push -r O
.. * hg push
..
.. Expected exchange:
..
.. * A (prune)
.. * B (prune)
Setup
-----
$ . $TESTDIR/testlib/exchange-obsmarker-util.sh
Initial
$ setuprepos C.1
creating test repo for test case C.1
- pulldest
- main
- pushdest
cd into `main` and proceed with env setup
$ cd main
$ mkcommit A
$ mkcommit B
$ hg prune -qd '0 0' '.~1'
1 new orphan changesets
$ hg prune -qd '0 0' .
$ hg log -G --hidden
x f6fbb35d8ac9 (draft): B
|
x f5bc6836db60 (draft): A
|
@ a9bdc8b26820 (public): O
$ inspect_obsmarkers
obsstore content
================
f5bc6836db60e308a17ba08bf050154ba9c4fad7 0 {a9bdc8b26820b1b87d585b82eb0ceb4a2ecdbc04} (Thu Jan 01 00:00:00 1970 +0000) {'user': 'test'}
f6fbb35d8ac958bbe70035e4c789c18471cdc0af 0 {f5bc6836db60e308a17ba08bf050154ba9c4fad7} (Thu Jan 01 00:00:00 1970 +0000) {'user': 'test'}
$ cd ..
$ cd ..
$ cp -R C.1 C.1.a
$ cp -R C.1 C.1.b
Actual Test (explicit push)
---------------------------
$ dotest C.1.a O
## Running testcase C.1.a
# testing echange of "O" (a9bdc8b26820)
## initial state
# obstore: main
f5bc6836db60e308a17ba08bf050154ba9c4fad7 0 {a9bdc8b26820b1b87d585b82eb0ceb4a2ecdbc04} (Thu Jan 01 00:00:00 1970 +0000) {'user': 'test'}
f6fbb35d8ac958bbe70035e4c789c18471cdc0af 0 {f5bc6836db60e308a17ba08bf050154ba9c4fad7} (Thu Jan 01 00:00:00 1970 +0000) {'user': 'test'}
# obstore: pushdest
# obstore: pulldest
## pushing "O" from main to pushdest
pushing to pushdest
searching for changes
no changes found
remote: 2 new obsolescence markers
## post push state
# obstore: main
f5bc6836db60e308a17ba08bf050154ba9c4fad7 0 {a9bdc8b26820b1b87d585b82eb0ceb4a2ecdbc04} (Thu Jan 01 00:00:00 1970 +0000) {'user': 'test'}
f6fbb35d8ac958bbe70035e4c789c18471cdc0af 0 {f5bc6836db60e308a17ba08bf050154ba9c4fad7} (Thu Jan 01 00:00:00 1970 +0000) {'user': 'test'}
# obstore: pushdest
f5bc6836db60e308a17ba08bf050154ba9c4fad7 0 {a9bdc8b26820b1b87d585b82eb0ceb4a2ecdbc04} (Thu Jan 01 00:00:00 1970 +0000) {'user': 'test'}
f6fbb35d8ac958bbe70035e4c789c18471cdc0af 0 {f5bc6836db60e308a17ba08bf050154ba9c4fad7} (Thu Jan 01 00:00:00 1970 +0000) {'user': 'test'}
# obstore: pulldest
## pulling "a9bdc8b26820" from main into pulldest
pulling from main
no changes found
2 new obsolescence markers
## post pull state
# obstore: main
f5bc6836db60e308a17ba08bf050154ba9c4fad7 0 {a9bdc8b26820b1b87d585b82eb0ceb4a2ecdbc04} (Thu Jan 01 00:00:00 1970 +0000) {'user': 'test'}
f6fbb35d8ac958bbe70035e4c789c18471cdc0af 0 {f5bc6836db60e308a17ba08bf050154ba9c4fad7} (Thu Jan 01 00:00:00 1970 +0000) {'user': 'test'}
# obstore: pushdest
f5bc6836db60e308a17ba08bf050154ba9c4fad7 0 {a9bdc8b26820b1b87d585b82eb0ceb4a2ecdbc04} (Thu Jan 01 00:00:00 1970 +0000) {'user': 'test'}
f6fbb35d8ac958bbe70035e4c789c18471cdc0af 0 {f5bc6836db60e308a17ba08bf050154ba9c4fad7} (Thu Jan 01 00:00:00 1970 +0000) {'user': 'test'}
# obstore: pulldest
f5bc6836db60e308a17ba08bf050154ba9c4fad7 0 {a9bdc8b26820b1b87d585b82eb0ceb4a2ecdbc04} (Thu Jan 01 00:00:00 1970 +0000) {'user': 'test'}
f6fbb35d8ac958bbe70035e4c789c18471cdc0af 0 {f5bc6836db60e308a17ba08bf050154ba9c4fad7} (Thu Jan 01 00:00:00 1970 +0000) {'user': 'test'}
Actual Test (bare push)
-------------------------------------
$ dotest C.1.b
## Running testcase C.1.b
## initial state
# obstore: main
f5bc6836db60e308a17ba08bf050154ba9c4fad7 0 {a9bdc8b26820b1b87d585b82eb0ceb4a2ecdbc04} (Thu Jan 01 00:00:00 1970 +0000) {'user': 'test'}
f6fbb35d8ac958bbe70035e4c789c18471cdc0af 0 {f5bc6836db60e308a17ba08bf050154ba9c4fad7} (Thu Jan 01 00:00:00 1970 +0000) {'user': 'test'}
# obstore: pushdest
# obstore: pulldest
## pushing from main to pushdest
pushing to pushdest
searching for changes
no changes found
remote: 2 new obsolescence markers
## post push state
# obstore: main
f5bc6836db60e308a17ba08bf050154ba9c4fad7 0 {a9bdc8b26820b1b87d585b82eb0ceb4a2ecdbc04} (Thu Jan 01 00:00:00 1970 +0000) {'user': 'test'}
f6fbb35d8ac958bbe70035e4c789c18471cdc0af 0 {f5bc6836db60e308a17ba08bf050154ba9c4fad7} (Thu Jan 01 00:00:00 1970 +0000) {'user': 'test'}
# obstore: pushdest
f5bc6836db60e308a17ba08bf050154ba9c4fad7 0 {a9bdc8b26820b1b87d585b82eb0ceb4a2ecdbc04} (Thu Jan 01 00:00:00 1970 +0000) {'user': 'test'}
f6fbb35d8ac958bbe70035e4c789c18471cdc0af 0 {f5bc6836db60e308a17ba08bf050154ba9c4fad7} (Thu Jan 01 00:00:00 1970 +0000) {'user': 'test'}
# obstore: pulldest
## pulling from main into pulldest
pulling from main
searching for changes
no changes found
2 new obsolescence markers
## post pull state
# obstore: main
f5bc6836db60e308a17ba08bf050154ba9c4fad7 0 {a9bdc8b26820b1b87d585b82eb0ceb4a2ecdbc04} (Thu Jan 01 00:00:00 1970 +0000) {'user': 'test'}
f6fbb35d8ac958bbe70035e4c789c18471cdc0af 0 {f5bc6836db60e308a17ba08bf050154ba9c4fad7} (Thu Jan 01 00:00:00 1970 +0000) {'user': 'test'}
# obstore: pushdest
f5bc6836db60e308a17ba08bf050154ba9c4fad7 0 {a9bdc8b26820b1b87d585b82eb0ceb4a2ecdbc04} (Thu Jan 01 00:00:00 1970 +0000) {'user': 'test'}
f6fbb35d8ac958bbe70035e4c789c18471cdc0af 0 {f5bc6836db60e308a17ba08bf050154ba9c4fad7} (Thu Jan 01 00:00:00 1970 +0000) {'user': 'test'}
# obstore: pulldest
f5bc6836db60e308a17ba08bf050154ba9c4fad7 0 {a9bdc8b26820b1b87d585b82eb0ceb4a2ecdbc04} (Thu Jan 01 00:00:00 1970 +0000) {'user': 'test'}
f6fbb35d8ac958bbe70035e4c789c18471cdc0af 0 {f5bc6836db60e308a17ba08bf050154ba9c4fad7} (Thu Jan 01 00:00:00 1970 +0000) {'user': 'test'}