# HG changeset patch # User Paul Morelle # Date 1529624558 -7200 # Node ID 44f5acfb9ad292a0426b24671feed17ffae42bf0 # Parent af8d8513d7de8240ff5d23b2a93fd1e6305aa034 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 -r af8d8513d7de -r 44f5acfb9ad2 mercurial/configitems.py --- a/mercurial/configitems.py Mon Jul 09 09:50:23 2018 -0400 +++ b/mercurial/configitems.py Fri Jun 22 01:42:38 2018 +0200 @@ -629,7 +629,7 @@ generic=True, ) coreconfigitem('format', 'aggressivemergedeltas', - default=False, + default=True, ) coreconfigitem('format', 'chunkcachesize', default=None, diff -r af8d8513d7de -r 44f5acfb9ad2 mercurial/revlog.py --- a/mercurial/revlog.py Mon Jul 09 09:50:23 2018 -0400 +++ b/mercurial/revlog.py Fri Jun 22 01:42:38 2018 +0200 @@ -615,7 +615,7 @@ # 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 -r af8d8513d7de -r 44f5acfb9ad2 tests/test-generaldelta.t --- a/tests/test-generaldelta.t Mon Jul 09 09:50:23 2018 -0400 +++ b/tests/test-generaldelta.t Fri Jun 22 01:42:38 2018 +0200 @@ -139,7 +139,7 @@ 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=