comparison mercurial/revlog.py @ 39087:f90b333e79cb

revlog: filter out "invalid" delta base candidates

There are bases that we know won't produce a good delta chain. For example, if
the base is already bigger than twice the size of the text we store, we know
the resulting delta chain will never be valid.

We might make the check a bit more powerful and generic in the future, but
this looks a good start.

In particular, empty file (size 0) will never find a good base, so we should
stop spending time trying to find one.

39086:64ddad2f26bb

        deltalength = self.revlog.length
        deltaparent = self.revlog.deltaparent

        deltainfo = None
        for candidaterevs in self._getcandidaterevs(p1, p2, cachedelta):
            nominateddeltas = []
            for candidaterev in candidaterevs:
                # skip over empty delta (no need to include them in a chain)
                while candidaterev != nullrev and not deltalength(candidaterev):
                    candidaterev = deltaparent(candidaterev)

39087:f90b333e79cb

        deltalength = self.revlog.length
        deltaparent = self.revlog.deltaparent

        deltainfo = None
        deltas_limit = revinfo.textlen * LIMIT_DELTA2TEXT
        for candidaterevs in self._getcandidaterevs(p1, p2, cachedelta):
            # filter out delta base that will never produce good delta
            candidaterevs = [r for r in candidaterevs
                             if self.revlog.length(r) <= deltas_limit]
            nominateddeltas = []
            for candidaterev in candidaterevs:
                # skip over empty delta (no need to include them in a chain)
                while candidaterev != nullrev and not deltalength(candidaterev):
                    candidaterev = deltaparent(candidaterev)