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parsers: a C implementation of the new ancestors algorithm...
parsers: a C implementation of the new ancestors algorithm The performance of both the old and new Python ancestor algorithms depends on the number of revs they need to traverse. Although the new algorithm performs far better than the old when revs are numerically and topologically close, both algorithms become slow under other circumstances, taking up to 1.8 seconds to give answers in a Linux kernel repo. This C implementation of the new algorithm is a fairly straightforward transliteration. The only corner case of interest is that it raises an OverflowError if the number of GCA candidates found during the first pass is greater than 24, to avoid the dual perils of fixnum overflow and trying to allocate too much memory. (If this exception is raised, the Python implementation is used instead.) Performance numbers are good: in a Linux kernel repo, time for "hg debugancestors" on two distant revs (24bf01de7537 and c2a8808f5943) is as follows: Old Python: 0.36 sec New Python: 0.42 sec New C: 0.02 sec For a case where the new algorithm should perform well: Old Python: 1.84 sec New Python: 0.07 sec New C: measures as zero when using --time (This commit includes a paranoid cross-check to ensure that the Python and C implementations give identical answers. The above performance numbers were measured with that check disabled.)

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revsets.txt
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Mercurial supports a functional language for selecting a set of
revisions.
The language supports a number of predicates which are joined by infix
operators. Parenthesis can be used for grouping.
Identifiers such as branch names may need quoting with single or
double quotes if they contain characters like ``-`` or if they match
one of the predefined predicates.
Special characters can be used in quoted identifiers by escaping them,
e.g., ``\n`` is interpreted as a newline. To prevent them from being
interpreted, strings can be prefixed with ``r``, e.g. ``r'...'``.
There is a single prefix operator:
``not x``
Changesets not in x. Short form is ``! x``.
These are the supported infix operators:
``x::y``
A DAG range, meaning all changesets that are descendants of x and
ancestors of y, including x and y themselves. If the first endpoint
is left out, this is equivalent to ``ancestors(y)``, if the second
is left out it is equivalent to ``descendants(x)``.
An alternative syntax is ``x..y``.
``x:y``
All changesets with revision numbers between x and y, both
inclusive. Either endpoint can be left out, they default to 0 and
tip.
``x and y``
The intersection of changesets in x and y. Short form is ``x & y``.
``x or y``
The union of changesets in x and y. There are two alternative short
forms: ``x | y`` and ``x + y``.
``x - y``
Changesets in x but not in y.
``x^n``
The nth parent of x, n == 0, 1, or 2.
For n == 0, x; for n == 1, the first parent of each changeset in x;
for n == 2, the second parent of changeset in x.
``x~n``
The nth first ancestor of x; ``x~0`` is x; ``x~3`` is ``x^^^``.
There is a single postfix operator:
``x^``
Equivalent to ``x^1``, the first parent of each changeset in x.
The following predicates are supported:
.. predicatesmarker
New predicates (known as "aliases") can be defined, using any combination of
existing predicates or other aliases. An alias definition looks like::
<alias> = <definition>
in the ``revsetalias`` section of a Mercurial configuration file. Arguments
of the form `$1`, `$2`, etc. are substituted from the alias into the
definition.
For example,
::
[revsetalias]
h = heads()
d($1) = sort($1, date)
rs($1, $2) = reverse(sort($1, $2))
defines three aliases, ``h``, ``d``, and ``rs``. ``rs(0:tip, author)`` is
exactly equivalent to ``reverse(sort(0:tip, author))``.
Command line equivalents for :hg:`log`::
-f -> ::.
-d x -> date(x)
-k x -> keyword(x)
-m -> merge()
-u x -> user(x)
-b x -> branch(x)
-P x -> !::x
-l x -> limit(expr, x)
Some sample queries:
- Changesets on the default branch::
hg log -r "branch(default)"
- Changesets on the default branch since tag 1.5 (excluding merges)::
hg log -r "branch(default) and 1.5:: and not merge()"
- Open branch heads::
hg log -r "head() and not closed()"
- Changesets between tags 1.3 and 1.5 mentioning "bug" that affect
``hgext/*``::
hg log -r "1.3::1.5 and keyword(bug) and file('hgext/*')"
- Changesets committed in May 2008, sorted by user::
hg log -r "sort(date('May 2008'), user)"
- Changesets mentioning "bug" or "issue" that are not in a tagged
release::
hg log -r "(keyword(bug) or keyword(issue)) and not ancestors(tag())"