comparison mercurial/commands.py @ 27263:4efb36ecaaec

commands: add debugdeltachain command

We have debug commands for displaying overall revlog statistics
(debugrevlog) and for dumping a revlog index (debugindex). As part
of investigating various aspects of revlog behavior and performance,
I found it important to have an understanding of how revlog
delta chains behave in practice.

This patch implements a "debugdeltachain" command. For each revision
in a revlog, it dumps information about the delta chain. Which delta
chain it is part of, length of the delta chain, distance since base
revision, info about base revision, size of the delta chain, etc. The
generic formatting facility is used, which means we can templatize
output and get machine readable output like JSON.

This command has already uncovered some weird history in
mozilla-central I didn't know about. So I think it's valuable.

27262:3d0feb2f978b

        ui.write("\t%d -> %d\n" % (r.rev(pp[0]), i))
        if pp[1] != nullid:
            ui.write("\t%d -> %d\n" % (r.rev(pp[1]), i))
    ui.write("}\n")

@command('debuginstall', [], '', norepo=True)
def debuginstall(ui):
    '''test Mercurial installation

    Returns 0 on success.

27263:4efb36ecaaec

        ui.write("\t%d -> %d\n" % (r.rev(pp[0]), i))
        if pp[1] != nullid:
            ui.write("\t%d -> %d\n" % (r.rev(pp[1]), i))
    ui.write("}\n")

@command('debugdeltachain',
    debugrevlogopts + formatteropts,
    _('-c|-m|FILE'),
    optionalrepo=True)
def debugdeltachain(ui, repo, file_=None, **opts):
    """dump information about delta chains in a revlog

    Output can be templatized. Available template keywords are:

       rev          revision number
       chainid      delta chain identifier (numbered by unique base)
       chainlen     delta chain length to this revision
       prevrev      previous revision in delta chain
       deltatype    role of delta / how it was computed
       compsize     compressed size of revision
       uncompsize   uncompressed size of revision
       chainsize    total size of compressed revisions in chain
       chainratio   total chain size divided by uncompressed revision size
                    (new delta chains typically start at ratio 2.00)
       lindist      linear distance from base revision in delta chain to end
                    of this revision
       extradist    total size of revisions not part of this delta chain from
                    base of delta chain to end of this revision; a measurement
                    of how much extra data we need to read/seek across to read
                    the delta chain for this revision
       extraratio   extradist divided by chainsize; another representation of
                    how much unrelated data is needed to load this delta chain
    """
    r = cmdutil.openrevlog(repo, 'debugdeltachain', file_, opts)
    index = r.index
    generaldelta = r.version & revlog.REVLOGGENERALDELTA

    def revinfo(rev):
        iterrev = rev
        e = index[iterrev]
        chain = []
        compsize = e[1]
        uncompsize = e[2]
        chainsize = 0

        if generaldelta:
            if e[3] == e[5]:
                deltatype = 'p1'
            elif e[3] == e[6]:
                deltatype = 'p2'
            elif e[3] == rev - 1:
                deltatype = 'prev'
            elif e[3] == rev:
                deltatype = 'base'
            else:
                deltatype = 'other'
        else:
            if e[3] == rev:
                deltatype = 'base'
            else:
                deltatype = 'prev'

        while iterrev != e[3]:
            chain.append(iterrev)
            chainsize += e[1]
            if generaldelta:
                iterrev = e[3]
            else:
                iterrev -= 1
            e = index[iterrev]
        else:
            chainsize += e[1]
            chain.append(iterrev)

        chain.reverse()
        return compsize, uncompsize, deltatype, chain, chainsize

    fm = ui.formatter('debugdeltachain', opts)

    fm.plain('    rev  chain# chainlen     prev   delta       '
             'size    rawsize  chainsize     ratio   lindist extradist '
             'extraratio\n')

    chainbases = {}
    for rev in r:
        comp, uncomp, deltatype, chain, chainsize = revinfo(rev)
        chainbase = chain[0]
        chainid = chainbases.setdefault(chainbase, len(chainbases) + 1)
        basestart = r.start(chainbase)
        revstart = r.start(rev)
        lineardist = revstart + comp - basestart
        extradist = lineardist - chainsize
        try:
            prevrev = chain[-2]
        except IndexError:
            prevrev = -1

        chainratio = float(chainsize) / float(uncomp)
        extraratio = float(extradist) / float(chainsize)

        fm.startitem()
        fm.write('rev chainid chainlen prevrev deltatype compsize '
                 'uncompsize chainsize chainratio lindist extradist '
                 'extraratio',
                 '%7d %7d %8d %8d %7s %10d %10d %10d %9.5f %9d %9d %10.5f\n',
                 rev, chainid, len(chain), prevrev, deltatype, comp,
                 uncomp, chainsize, chainratio, lineardist, extradist,
                 extraratio,
                 rev=rev, chainid=chainid, chainlen=len(chain),
                 prevrev=prevrev, deltatype=deltatype, compsize=comp,
                 uncompsize=uncomp, chainsize=chainsize,
                 chainratio=chainratio, lindist=lineardist,
                 extradist=extradist, extraratio=extraratio)

    fm.end()

@command('debuginstall', [], '', norepo=True)
def debuginstall(ui):
    '''test Mercurial installation

    Returns 0 on success.