[PATCH 2 of 3] revset: add an undocumented _missingancestors function

[Lucas Moscovicz]

On 2/15/14, 10:41 PM, "Siddharth Agarwal" <sid0 at fb.com> wrote:

>On 02/14/2014 10:55 AM, Durham Goode wrote:
>> On 2/13/14 2:10 PM, "Siddharth Agarwal" <sid0 at fb.com> wrote:
>>
>>> # HG changeset patch
>>> # User Siddharth Agarwal <sid0 at fb.com>
>>> # Date 1392328485 28800
>>> #      Thu Feb 13 13:54:45 2014 -0800
>>> # Node ID b23315bb97257c5a8c2a6810990b19f5aa1dd2c7
>>> # Parent  36f133144674e0f91b4c16d3ca49c01b3046f572
>>> revset: add an undocumented _missingancestors function
>>>
>>> This will be used in an upcoming patch to optimize expressions of the
>>>form
>>> (::x - ::y).
>>>
>>> diff --git a/mercurial/revset.py b/mercurial/revset.py
>>> --- a/mercurial/revset.py
>>> +++ b/mercurial/revset.py
>>> @@ -1021,6 +1021,16 @@
>>>              return baseset([m])
>>>      return baseset([])
>>>
>>> +def _missingancestors(repo, subset, x):
>>> +    # i18n: "_missingancestors" is a keyword
>>> +    revs, bases = getargs(x, 2, 2,
>>> +                          _("_missingancestors requires two
>>>arguments"))
>>> +    rs = baseset(repo)
>>> +    revs = getset(repo, rs, revs)
>>> +    bases = getset(repo, rs, bases)
>>> +    missing = set(repo.changelog.findmissingrevs(bases, revs))
>>> +    return baseset([r for r in subset if r in missing])
>>> +
>> You could use the new 'lazyset' class for the return value here, so we
>> don't have to iterate over the entire subset immediately.
>>
>
>I replaced the baseset line with
>
>     return lazyset(subset, lambda r: r in missing)
>
>and perfrevset on the revset '::tip - ::-10000' (performed in the next
>patch) is significantly worse:
>
>! wall 0.232009 comb 0.240000 user 0.230000 sys 0.010000 (best of 42)
>
>Looking at the profile, it seems like the entire set is materialized, so
>the lambda function calls only slow things down. Am I missing something?

At this point the code in scmutil and cmdutil has not been changed yet to
work with lazy implementations and the entire set is still being
materialized there, so probably the only way to see a difference so far
would be if you try Œfirst(::tip - ::-10000)¹ which will return as fast as
the first value is produced.

I¹ve been working this days to change that code to be able to have those
lazy results without having to limit the expression.

>
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