comparison mercurial/revlogutils/deltas.py @ 40603:2f7e531ef3e7

sparse-revlog: skip the span check in the sparse-revlog case

This significantly improves the performance on unbundling on smaller
repositories.

Mercurial: unbundling 1K revisions

    no-sparse-revlog:     500 ms
    sparse-revlog-before: 689 ms
    sparse-revlog-after:  484 ms

Pypy: unbundling 1K revisions

    no-sparse-revlog:     1.242 s
    sparse-revlog-before: 1.135 s
    sparse-revlog-after:  0.860 s

NetBeans: unbundling 1K revisions

    no-sparse-revlog:     1.386 s
    sparse-revlog-before: 2.368 s
    sparse-revlog-after:  1.191 s

Mozilla: unbundling 1K revisions

    no-sparse-revlog:     3.103 s
    sparse-revlog-before: 3.367 s
    sparse-revlog-after:  3.093 s

40602:c36175456350

    #   bounding it limits the amount of I/O we need to do.
    # - 'deltainfo.compresseddeltalen' is the sum of the total size of
    #   deltas we need to apply -- bounding it limits the amount of CPU
    #   we consume.

    if revlog._sparserevlog:
        # As sparse-read will be used, we can consider that the distance,
        # instead of being the span of the whole chunk,
        # is the span of the largest read chunk
        base = deltainfo.base

        if base != nullrev:
            deltachain = revlog._deltachain(base)[0]
        else:
            deltachain = []

        # search for the first non-snapshot revision
        for idx, r in enumerate(deltachain):
            if not revlog.issnapshot(r):
                break
        deltachain = deltachain[idx:]
        chunks = slicechunk(revlog, deltachain, deltainfo)
        all_span = [segmentspan(revlog, revs, deltainfo)
                    for revs in chunks]
        distance = max(all_span)
    else:
        distance = deltainfo.distance

    textlen = revinfo.textlen
    defaultmax = textlen * 4
    maxdist = revlog._maxdeltachainspan
    if not maxdist:
        maxdist = distance # ensure the conditional pass
    maxdist = max(maxdist, defaultmax)
    if revlog._sparserevlog and maxdist < revlog._srmingapsize:
        # In multiple place, we are ignoring irrelevant data range below a
        # certain size. Be also apply this tradeoff here and relax span
        # constraint for small enought content.
        maxdist = revlog._srmingapsize

    # Bad delta from read span:
    #
    #   If the span of data read is larger than the maximum allowed.
    if maxdist < distance:
        return False

    # Bad delta from new delta size:
    #
    #   If the delta size is larger than the target text, storing the

40603:2f7e531ef3e7

    #   bounding it limits the amount of I/O we need to do.
    # - 'deltainfo.compresseddeltalen' is the sum of the total size of
    #   deltas we need to apply -- bounding it limits the amount of CPU
    #   we consume.

    textlen = revinfo.textlen
    defaultmax = textlen * 4
    maxdist = revlog._maxdeltachainspan
    if not maxdist:
        maxdist = deltainfo.distance # ensure the conditional pass
    maxdist = max(maxdist, defaultmax)

    # Bad delta from read span:
    #
    #   If the span of data read is larger than the maximum allowed.
    #
    #   In the sparse-revlog case, we rely on the associated "sparse reading"
    #   to avoid issue related to the span of data. In theory, it would be
    #   possible to build pathological revlog where delta pattern would lead
    #   to too many reads. However, they do not happen in practice at all. So
    #   we skip the span check entirely.
    if not revlog._sparserevlog and maxdist < deltainfo.distance:
        return False

    # Bad delta from new delta size:
    #
    #   If the delta size is larger than the target text, storing the