view contrib/perf-utils/subsetmaker.py @ 49491:c6a1beba27e9

bisect: avoid copying ancestor list for non-merge commits

During a bisection, hg needs to compute a list of all ancestors for every
candidate commit. This is accomplished via a bottom-up traversal of the set of
candidates, during which each revision's ancestor list is populated using the
ancestor list of its parent(s). Previously, this involved copying the entire
list, which could be very long in if the bisection range was large.

To help improve this, we can observe that each candidate commit is visited
exactly once, at which point its ancestor list is copied into its children's
lists and then dropped. In the case of non-merge commits, a commit's ancestor
list consists exactly of its parent's list plus itself. This means that we can
trivially reuse the parent's existing list for one of its non-merge children,
which avoids copying entirely if that commit is the parent's only child. This
makes bisections over linear ranges of commits much faster.

During some informal testing in the large publicly-available `mozilla-central`
repository, this noticeably sped up bisections over large ranges of history:

Setup:
  $ cd mozilla-central
  $ hg bisect --reset
  $ hg bisect --good 0
  $ hg log -r tip -T '{rev}\n'
  628417

Test:
  $ time hg bisect --bad tip --noupdate

Before:
  real    3m35.927s
  user    3m35.553s
  sys     0m0.319s

After:
  real    1m41.142s
  user    1m40.810s
  sys     0m0.285s

"""revset to select sample of repository

Hopefully this is useful to create interesting discovery cases.
"""

import collections
import random

from mercurial.i18n import _

from mercurial import (
    registrar,
    revset,
    revsetlang,
    smartset,
)

import sortedcontainers

SortedSet = sortedcontainers.SortedSet

revsetpredicate = registrar.revsetpredicate()


@revsetpredicate(b'subsetspec("<spec>")')
def subsetmarkerspec(repo, subset, x):
    """use a shorthand spec as used by search-discovery-case

    Supported format are:

    - "scratch-count-seed": not scratch(all(), count, "seed")
    - "randomantichain-seed": ::randomantichain(all(), "seed")
    - "rev-REV": "::REV"
    """
    args = revsetlang.getargs(
        x, 0, 1, _(b'subsetspec("spec") required an argument')
    )

    spec = revsetlang.getstring(args[0], _(b"spec should be a string"))
    case = spec.split(b'-')
    t = case[0]
    if t == b'scratch':
        spec_revset = b'not scratch(all(), %s, "%s")' % (case[1], case[2])
    elif t == b'randomantichain':
        spec_revset = b'::randomantichain(all(), "%s")' % case[1]
    elif t == b'rev':
        spec_revset = b'::%d' % case[1]
    else:
        assert False, spec

    selected = repo.revs(spec_revset)

    return selected & subset


@revsetpredicate(b'scratch(REVS, <count>, [seed])')
def scratch(repo, subset, x):
    """randomly remove <count> revision from the repository top

    This subset is created by recursively picking changeset starting from the
    heads. It can be summarized using the following algorithm::

        selected = set()
        for i in range(<count>):
            unselected = repo.revs("not <selected>")
            candidates = repo.revs("heads(<unselected>)")
            pick = random.choice(candidates)
            selected.add(pick)
    """
    m = _(b"scratch expects revisions, count argument and an optional seed")
    args = revsetlang.getargs(x, 2, 3, m)
    if len(args) == 2:
        x, n = args
        rand = random
    elif len(args) == 3:
        x, n, seed = args
        seed = revsetlang.getinteger(seed, _(b"seed should be a number"))
        rand = random.Random(seed)
    else:
        assert False

    n = revsetlang.getinteger(n, _(b"scratch expects a number"))

    selected = set()
    heads = SortedSet()
    children_count = collections.defaultdict(lambda: 0)
    parents = repo.changelog._uncheckedparentrevs

    baseset = revset.getset(repo, smartset.fullreposet(repo), x)
    baseset.sort()
    for r in baseset:
        heads.add(r)

        p1, p2 = parents(r)
        if p1 >= 0:
            heads.discard(p1)
            children_count[p1] += 1
        if p2 >= 0:
            heads.discard(p2)
            children_count[p2] += 1

    for h in heads:
        assert children_count[h] == 0

    selected = set()
    for x in range(n):
        if not heads:
            break
        pick = rand.choice(heads)
        heads.remove(pick)
        assert pick not in selected
        selected.add(pick)
        p1, p2 = parents(pick)
        if p1 in children_count:
            assert p1 in children_count
            children_count[p1] -= 1
            assert children_count[p1] >= 0
            if children_count[p1] == 0:
                assert p1 not in selected, (r, p1)
                heads.add(p1)
        if p2 in children_count:
            assert p2 in children_count
            children_count[p2] -= 1
            assert children_count[p2] >= 0
            if children_count[p2] == 0:
                assert p2 not in selected, (r, p2)
                heads.add(p2)

    return smartset.baseset(selected) & subset


@revsetpredicate(b'randomantichain(REVS, [seed])')
def antichain(repo, subset, x):
    """Pick a random anti-chain in the repository

    A antichain is a set of changeset where there isn't any element that is
    either a descendant or ancestors of any other element in the set. In other
    word, all the elements are independant. It can be summarized with the
    following algorithm::

    selected = set()
    unselected = repo.revs('all()')
    while unselected:
        pick = random.choice(unselected)
        selected.add(pick)
        unselected -= repo.revs('::<pick> + <pick>::')
    """

    args = revsetlang.getargs(
        x, 1, 2, _(b"randomantichain expects revisions and an optional seed")
    )
    if len(args) == 1:
        (x,) = args
        rand = random
    elif len(args) == 2:
        x, seed = args
        seed = revsetlang.getinteger(seed, _(b"seed should be a number"))
        rand = random.Random(seed)
    else:
        assert False

    cl = repo.changelog

    # We already have cheap access to the parent mapping.
    # However, we need to build a mapping of the children mapping
    parents = repo.changelog._uncheckedparentrevs
    children_map = collections.defaultdict(list)
    for r in cl:
        p1, p2 = parents(r)
        if p1 >= 0:
            children_map[p1].append(r)
        if p2 >= 0:
            children_map[p2].append(r)
    children = children_map.__getitem__

    selected = set()
    undecided = SortedSet(cl)

    while undecided:
        # while there is "undecided content", we pick a random changeset X
        # and we remove anything in `::X + X::` from undecided content
        pick = rand.choice(undecided)
        selected.add(pick)
        undecided.remove(pick)

        ancestors = set(p for p in parents(pick) if p in undecided)
        descendants = set(c for c in children(pick) if c in undecided)

        while ancestors:
            current = ancestors.pop()
            undecided.remove(current)
            for p in parents(current):
                if p in undecided:
                    ancestors.add(p)
        while descendants:
            current = descendants.pop()
            undecided.remove(current)
            for p in children(current):
                if p in undecided:
                    ancestors.add(p)

    return smartset.baseset(selected) & subset