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Differential D5197

sparse-revlog: only refine delta candidates in the sparse case (issue6006)
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Authored by lothiraldan on Oct 31 2018, 6:18 AM.

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rHGbafa1c4bb7a8: sparse-revlog: only refine delta candidates in the sparse case (issue6006)
Summary

Starting with 5aef5afa8654, a valid delta parent might be "refined". This
allows repository using sparse-revlog to produce better delta chain by using
better intermediate snapshot base.

However, this refining step was performed in all cases, including for
repository not using sparse-revlog. This could produce a strange chain in the
general delta case and corrupted repository in the non-general delta case.

We now skip this step unless sparse-revlog is in use.

In issue 6006, Yuya Nishihara provided a test case using an external
repository, so we did not include it. Finding "laboratory" condition to
reproduce this case and implementing an efficient test reproducing it is a bit
tricky. We do not foresee to have the time to provide one by the release date.

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lothiraldan created this revision.Oct 31 2018, 6:18 AM
Closed by commit rHGbafa1c4bb7a8: sparse-revlog: only refine delta candidates in the sparse case (issue6006) (authored by lothiraldan). · Explain WhyOct 31 2018, 7:58 AM
This revision was automatically updated to reflect the committed changes.

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Mmercurial/revlogutils/deltas.py (5 lines)

Diff 12347

mercurial/revlogutils/deltas.py

if good is not None: if good is not None:
yield None yield None
return return
for candidates in _rawgroups(revlog, p1, p2, cachedelta): for candidates in _rawgroups(revlog, p1, p2, cachedelta):
good = yield candidates good = yield candidates
if good is not None: if good is not None:
break break
# If sparse revlog is enabled, we can try to refine the available deltas
if not revlog._sparserevlog:
yield None
return
# if we have a refinable value, try to refine it # if we have a refinable value, try to refine it
if good is not None and good not in (p1, p2) and revlog.issnapshot(good): if good is not None and good not in (p1, p2) and revlog.issnapshot(good):
# refine snapshot down # refine snapshot down
previous = None previous = None
while previous != good: while previous != good:
previous = good previous = good
base = revlog.deltaparent(good) base = revlog.deltaparent(good)
if base == nullrev: if base == nullrev: