[PATCH 05 of 10] deltas: skip if projected delta size is bigger than previous snapshot
Pierre-Yves David
pierre-yves.david at ens-lyon.org
Thu Jun 13 13:23:00 UTC 2019
# HG changeset patch
# User Valentin Gatien-Baron <vgatien-baron at janestreet.com>
# Date 1556225433 -7200
# Thu Apr 25 22:50:33 2019 +0200
# Node ID c1659d13be53808661913cfd5b552bbbe4df9f1d
# Parent 614e5f26fcffcd74c601bb51b54bfb2378135f61
# EXP-Topic delta-extra
# Available At https://bitbucket.org/octobus/mercurial-devel/
# hg pull https://bitbucket.org/octobus/mercurial-devel/ -r c1659d13be53
deltas: skip if projected delta size is bigger than previous snapshot
Before computing any delta, we get a basic estimation of the delta size we can
expect and the resulted compressed value. We then checks this projected size
against the `size(snapshotⁿ) > size(snapshotⁿ⁺¹)` constraint. This allows to
exclude potential base candidates before doing any expensive computation.
This only apply to the intermediate-snapshot case since this constraint only
apply to them.
For some pathological cases of a private repository this step provide a
significant performance boost (timing from `hg perfrevlogwrite`):
before: 14.115908 seconds
after: 3.145906 seconds
diff --git a/mercurial/revlogutils/deltas.py b/mercurial/revlogutils/deltas.py
--- a/mercurial/revlogutils/deltas.py
+++ b/mercurial/revlogutils/deltas.py
@@ -698,6 +698,12 @@ def _candidategroups(revlog, textlen, p1
# delta lower bound is larger than accepted upper bound
continue
+ # check the relative constraint on the delta size
+ revlength = revlog.length(rev)
+ if revlength < lowestrealisticdeltalen:
+ # delta probable lower bound is larger than target base
+ continue
+
group.append(rev)
if group:
# XXX: in the sparse revlog case, group can become large,
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