[PATCH] aggressivemergedeltas: enabled the option by default
Boris Feld
boris.feld at octobus.net
Mon Jul 9 13:35:39 UTC 2018
# HG changeset patch
# User Paul Morelle <paul.morelle at octobus.net>
# Date 1529624558 -7200
# Fri Jun 22 01:42:38 2018 +0200
# Node ID 799439bbfcc194238ff4af2979eb286c5defdc3f
# Parent a0e185f104541858a0b049e1fb67c4d113930a9a
# EXP-Topic enable-aggressivemergedeltas
# Available At https://bitbucket.org/octobus/mercurial-devel/
# hg pull https://bitbucket.org/octobus/mercurial-devel/ -r 799439bbfcc1
aggressivemergedeltas: enabled the option by default
The option has been around for a while (August 2015) but was never turned on by
default. In-depth testing shows large wins for having that on with no
significant drawbacks.
When enabled, revlog consider delta against both p1 and p2 at the same time when
storing a revision. Selecting a delta against "p2" can produce better deltas and
chain. This raise large benefit for all repositories, especially if they have a
lot of merges.
Comparison of `.hg/store/` size:
mercurial (6.74% merges):
before: 54,225,348 bytes
after: 47,279,959 bytes -13%
pypy (8.30% merges):
before: 459,041,759 bytes
after: 346,090,067 bytes -25%
netbeans (34.21% merges):
before: 2,468,041,333 bytes
after: 1,364,077,645 bytes -45%
mozilla-central (4.84% merges):
before: 2,731,799,546 bytes
after: 2,157,718,019 bytes -21%
Comparison of `00manifest.d` size:
mercurial (6.74% merges):
before: 11,682,516 bytes
after: 6,143,044 bytes -47%
pypy (8.30% merges):
before: 156,447,163 bytes
after: 52,941,780 bytes -66%
netbeans (34.21% merges):
before: 1,250,363,851 bytes
after: 130,088,982 bytes -90%
mozilla-central (4.84% merges):
before: 468,202,733 bytes
after: 215,096,339 bytes -54%
In addition, the better deltas help with the performance of multiple core
operations. However, better chains mean longer chains, which can affect
performance negatively (mostly manifest revision retrieval time). Chains length
is a deeper problem that also affects linear repository too. Overall we think
the benefits of using p2 as a diff target are bigger than the downsizes. In
addition, we are also working on ways to improve the performance impact of chain
length, so theses downsizes get fixed in the future.
Below are interesting items from the full benchmark run:
bundling 100 revisions from pypy:
before: 670ms
after: 480ms -28%
bundle 10000 revisions from pypy:
before: 1.38s
after: 1.10s -54%
bundle 10000 revisions from pypy:
before: 16.1s
after: 7.81s -52%
bundle 10000 revisions from netbeans:
before: 19.3s
after: 15.5s -19%
unbundle 1000 revisions to pypy:
before: 641ms
after: 315ms - 51%
clone mercurial (http):
before: 26.0s
after: 22.6s -23%
pulling 1000 revisions from pypy (shh):
before: 2.07s
after: 1.36s -44%
pushing 1000 revision through http (pypy repository)
before: 2.18s
after: 1.35s -48%
diff time in mozilla-central:
before: 1.420s
after: 0.983s -31%
status time in mozilla-central:
before: 1.260s
after: 0.828s -34%
Impact in other cases seems minimal (within a couple of percent in worse cases)
and can be seen in both direction:
Timing for a simple `hg commit`:
mozilla-central:
before: 3.37s
after: 3.22s -4%
pypy:
before: 194ms
after: 197ms +2%
Timing for status (from tip to parent of tip):
mercurial:
before: 52.4ms
after: 52.4ms (same)
pypy:
before: 55.2
after: 56.9 +3%
Timing for `hg update`
mozilla-central, across 10 revisions:
before: 4.82s
after: 4.59s -5%
mozilla-central, across 10000 revisions:
before: 49.1s
after: 49.9s +2%
pypy, across 10 revisions:
before: 213ms
after: 216ms +1%
pypy, across 10000 revisions:
before: 5.31ms
after: 5.24ms -1%
The negative consequences are related to manifest fetch time:
(timing for the tip revision tested by the benchmark)
pypy-2018:
before: 2.60ms
after: 3.88ms +50%
mozilla-central-2018:
before: 565ms
after: 652ms +15% (~+100ms)
netbeans-2018:
before: 101ms
after: 250ms +48% (~+150ms)
This shows up as a fixed overhead on some command we benchmarked:
no-op push of mozilla-central:
before: 945ms
after: 1040ms +10% (~+100ms)
pushing 10 changeset in netbeabs over ssh:
before: 557ms
after: 712ms +28% (+155ms)
pushing 100 changeset in netbeabs over ssh:
before: 592ms
after: 771ms +30% (+179ms)
diff --git a/mercurial/configitems.py b/mercurial/configitems.py
--- a/mercurial/configitems.py
+++ b/mercurial/configitems.py
@@ -617,7 +617,7 @@ coreconfigitem('extdata', '.*',
generic=True,
)
coreconfigitem('format', 'aggressivemergedeltas',
- default=False,
+ default=True,
)
coreconfigitem('format', 'chunkcachesize',
default=None,
diff --git a/mercurial/revlog.py b/mercurial/revlog.py
--- a/mercurial/revlog.py
+++ b/mercurial/revlog.py
@@ -615,7 +615,7 @@ class revlog(object):
# How much data to read and cache into the raw revlog data cache.
self._chunkcachesize = 65536
self._maxchainlen = None
- self._aggressivemergedeltas = False
+ self._aggressivemergedeltas = True
self.index = []
# Mapping of partial identifiers to full nodes.
self._pcache = {}
diff --git a/tests/test-generaldelta.t b/tests/test-generaldelta.t
--- a/tests/test-generaldelta.t
+++ b/tests/test-generaldelta.t
@@ -139,7 +139,7 @@ Test format.aggressivemergedeltas
rev chain# chainlen prev delta size rawsize chainsize ratio lindist extradist extraratio
0 1 1 -1 base 59 215 59 0.27442 59 0 0.00000
1 1 2 0 prev 61 86 120 1.39535 120 0 0.00000
- 2 1 3 1 p1 65 301 185 0.61462 185 0 0.00000
+ 2 1 2 0 p2 62 301 121 0.40199 182 61 0.50413
$ hg strip -q -r . --config extensions.strip=
More information about the Mercurial-devel
mailing list