/brz/remove-bazaar

# groupcompress, a bzr plugin providing improved disk utilisation

# Copyright (C) 2008 Canonical Limited.

# 

# This program is free software; you can redistribute it and/or modify

# it under the terms of the GNU General Public License version 2 as published

# by the Free Software Foundation.

# 

# This program is distributed in the hope that it will be useful,

# but WITHOUT ANY WARRANTY; without even the implied warranty of

# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

# GNU General Public License for more details.

# 

# You should have received a copy of the GNU General Public License

# along with this program; if not, write to the Free Software

# Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA

# 

"""Repostory formats using B+Tree indices and groupcompress compression."""

import md5

import time

from bzrlib import (

    debug,

    errors,

    knit,

    inventory,

    pack,

    repository,

    trace,

    ui,

    )

from bzrlib.btree_index import (

    BTreeBuilder,

    BTreeGraphIndex,

    )

from bzrlib.index import GraphIndex, GraphIndexBuilder

from bzrlib.repository import InterPackRepo

from bzrlib.plugins.groupcompress.groupcompress import (

    _GCGraphIndex,

    GroupCompressVersionedFiles,

    )

from bzrlib.osutils import rand_chars

from bzrlib.repofmt.pack_repo import (

    Pack,

    NewPack,

    KnitPackRepository,

    RepositoryPackCollection,

    RepositoryFormatKnitPack6,

    RepositoryFormatKnitPack6RichRoot,

    Packer,

    ReconcilePacker,

    OptimisingPacker,

    )

try:

    from bzrlib.repofmt.pack_repo import (

    CHKInventoryRepository,

    RepositoryFormatPackDevelopment5,

    RepositoryFormatPackDevelopment5Hash16,

##    RepositoryFormatPackDevelopment5Hash16b,

##    RepositoryFormatPackDevelopment5Hash63,

##    RepositoryFormatPackDevelopment5Hash127a,

##    RepositoryFormatPackDevelopment5Hash127b,

    RepositoryFormatPackDevelopment5Hash255,

    )

    from bzrlib import chk_map

    chk_support = True

except ImportError:

    chk_support = False

def open_pack(self):

    return self._pack_collection.pack_factory(self._pack_collection,

        upload_suffix=self.suffix,

        file_mode=self._pack_collection.repo.bzrdir._get_file_mode())

Packer.open_pack = open_pack

class GCPack(NewPack):

    def __init__(self, pack_collection, upload_suffix='', file_mode=None):

        """Create a NewPack instance.

        :param pack_collection: A PackCollection into which this is being

            inserted.

        :param upload_suffix: An optional suffix to be given to any temporary

            files created during the pack creation. e.g '.autopack'

        :param file_mode: An optional file mode to create the new files with.

        """

        # replaced from bzr.dev to:

        # - change inventory reference list length to 1

        # - change texts reference lists to 1

        # TODO: patch this to be parameterised upstream

        # The relative locations of the packs are constrained, but all are

        # passed in because the caller has them, so as to avoid object churn.

        index_builder_class = pack_collection._index_builder_class

        if chk_support:

            # from brisbane-core

            if pack_collection.chk_index is not None:

                chk_index = index_builder_class(reference_lists=0)

            else:

                chk_index = None

            Pack.__init__(self,

                # Revisions: parents list, no text compression.

                index_builder_class(reference_lists=1),

                # Inventory: We want to map compression only, but currently the

                # knit code hasn't been updated enough to understand that, so we

                # have a regular 2-list index giving parents and compression

                # source.

                index_builder_class(reference_lists=1),

                # Texts: compression and per file graph, for all fileids - so two

                # reference lists and two elements in the key tuple.

                index_builder_class(reference_lists=1, key_elements=2),

                # Signatures: Just blobs to store, no compression, no parents

                # listing.

                index_builder_class(reference_lists=0),

                # CHK based storage - just blobs, no compression or parents.

                chk_index=chk_index

                )

        else:

            # from bzr.dev

            Pack.__init__(self,

                # Revisions: parents list, no text compression.

                index_builder_class(reference_lists=1),

                # Inventory: compressed, with graph for compatibility with other

                # existing bzrlib code.

                index_builder_class(reference_lists=1),

                # Texts: per file graph:

                index_builder_class(reference_lists=1, key_elements=2),

                # Signatures: Just blobs to store, no compression, no parents

                # listing.

                index_builder_class(reference_lists=0),

                )

        self._pack_collection = pack_collection

        # When we make readonly indices, we need this.

        self.index_class = pack_collection._index_class

        # where should the new pack be opened

        self.upload_transport = pack_collection._upload_transport

        # where are indices written out to

        self.index_transport = pack_collection._index_transport

        # where is the pack renamed to when it is finished?

        self.pack_transport = pack_collection._pack_transport

        # What file mode to upload the pack and indices with.

        self._file_mode = file_mode

        # tracks the content written to the .pack file.

        self._hash = md5.new()

        # a four-tuple with the length in bytes of the indices, once the pack

        # is finalised. (rev, inv, text, sigs)

        self.index_sizes = None

        # How much data to cache when writing packs. Note that this is not

        # synchronised with reads, because it's not in the transport layer, so

        # is not safe unless the client knows it won't be reading from the pack

        # under creation.

        self._cache_limit = 0

        # the temporary pack file name.

        self.random_name = rand_chars(20) + upload_suffix

        # when was this pack started ?

        self.start_time = time.time()

        # open an output stream for the data added to the pack.

        self.write_stream = self.upload_transport.open_write_stream(

            self.random_name, mode=self._file_mode)

        if 'pack' in debug.debug_flags:

            trace.mutter('%s: create_pack: pack stream open: %s%s t+%6.3fs',

                time.ctime(), self.upload_transport.base, self.random_name,

                time.time() - self.start_time)

        # A list of byte sequences to be written to the new pack, and the 

        # aggregate size of them.  Stored as a list rather than separate 

        # variables so that the _write_data closure below can update them.

        self._buffer = [[], 0]

        # create a callable for adding data 

        #

        # robertc says- this is a closure rather than a method on the object

        # so that the variables are locals, and faster than accessing object

        # members.

        def _write_data(bytes, flush=False, _buffer=self._buffer,

            _write=self.write_stream.write, _update=self._hash.update):

            _buffer[0].append(bytes)

            _buffer[1] += len(bytes)

            # buffer cap

            if _buffer[1] > self._cache_limit or flush:

                bytes = ''.join(_buffer[0])

                _write(bytes)

                _update(bytes)

                _buffer[:] = [[], 0]

        # expose this on self, for the occasion when clients want to add data.

        self._write_data = _write_data

        # a pack writer object to serialise pack records.

        self._writer = pack.ContainerWriter(self._write_data)

        self._writer.begin()

        # what state is the pack in? (open, finished, aborted)

        self._state = 'open'

RepositoryPackCollection.pack_factory = NewPack

class GCRepositoryPackCollection(RepositoryPackCollection):

    pack_factory = GCPack

    def _make_index(self, name, suffix):

        """Overridden to use BTreeGraphIndex objects."""

        size_offset = self._suffix_offsets[suffix]

        index_name = name + suffix

        index_size = self._names[name][size_offset]

        return BTreeGraphIndex(

            self._index_transport, index_name, index_size)

    def _start_write_group(self):

        # Overridden to add 'self.pack_factory()'

        # Do not permit preparation for writing if we're not in a 'write lock'.

        if not self.repo.is_write_locked():

            raise errors.NotWriteLocked(self)

        self._new_pack = self.pack_factory(self, upload_suffix='.pack',

            file_mode=self.repo.bzrdir._get_file_mode())

        # allow writing: queue writes to a new index

        self.revision_index.add_writable_index(self._new_pack.revision_index,

            self._new_pack)

        self.inventory_index.add_writable_index(self._new_pack.inventory_index,

            self._new_pack)

        self.text_index.add_writable_index(self._new_pack.text_index,

            self._new_pack)

        self.signature_index.add_writable_index(self._new_pack.signature_index,

            self._new_pack)

        if chk_support and self.chk_index is not None:

            self.chk_index.add_writable_index(self._new_pack.chk_index,

                self._new_pack)

            self.repo.chk_bytes._index._add_callback = self.chk_index.add_callback

        self.repo.inventories._index._add_callback = self.inventory_index.add_callback

        self.repo.revisions._index._add_callback = self.revision_index.add_callback

        self.repo.signatures._index._add_callback = self.signature_index.add_callback

        self.repo.texts._index._add_callback = self.text_index.add_callback

    def _get_filtered_inv_stream(self, source_vf, keys):

        """Filter the texts of inventories, to find the chk pages."""

        id_roots = []

        p_id_roots = []

        id_roots_set = set()

        p_id_roots_set = set()

        def _filter_inv_stream(stream):

            for idx, record in enumerate(stream):

                ### child_pb.update('fetch inv', idx, len(inv_keys_to_fetch))

                bytes = record.get_bytes_as('fulltext')

                chk_inv = inventory.CHKInventory.deserialise(None, bytes, record.key)

                key = chk_inv.id_to_entry.key()

                if key not in id_roots_set:

                    id_roots.append(key)

                    id_roots_set.add(key)

                p_id_map = chk_inv.parent_id_basename_to_file_id

                if p_id_map is not None:

                    key = p_id_map.key()

                    if key not in p_id_roots_set:

                        p_id_roots_set.add(key)

                        p_id_roots.append(key)

                yield record

        stream = source_vf.get_record_stream(keys, 'gc-optimal', True)

        return _filter_inv_stream(stream), id_roots, p_id_roots

    def _get_chk_stream(self, source_vf, keys, id_roots, p_id_roots, pb=None):

        # We want to stream the keys from 'id_roots', and things they

        # reference, and then stream things from p_id_roots and things they

        # reference, and then any remaining keys that we didn't get to.

        # We also group referenced texts together, so if one root references a

        # text with prefix 'a', and another root references a node with prefix

        # 'a', we want to yield those nodes before we yield the nodes for 'b'

        # This keeps 'similar' nodes together.

        # Note: We probably actually want multiple streams here, to help the

        #       client understand that the different levels won't compress well

        #       against each other.

        #       Test the difference between using one Group per level, and

        #       using 1 Group per prefix. (so '' (root) would get a group, then

        #       all the references to search-key 'a' would get a group, etc.)

        remaining_keys = set(keys)

        counter = [0]

        def _get_referenced_stream(root_keys):

            cur_keys = root_keys

            while cur_keys:

                keys_by_search_prefix = {}

                remaining_keys.difference_update(cur_keys)

                next_keys = set()

                stream = source_vf.get_record_stream(cur_keys, 'as-requested',

                                                     True)

                def next_stream():

                    for record in stream:

                        bytes = record.get_bytes_as('fulltext')

                        # We don't care about search_key_func for this code,

                        # because we only care about external references.

                        node = chk_map._deserialise(bytes, record.key,

                                                    search_key_func=None)

                        common_base = node._search_prefix

                        if isinstance(node, chk_map.InternalNode):

                            for prefix, value in node._items.iteritems():

                                if not isinstance(value, tuple):

                                    raise AssertionError("value is %s when"

                                        " tuple expected" % (value.__class__))

                                if value not in next_keys:

                                    keys_by_search_prefix.setdefault(prefix,

                                        []).append(value)

                                    next_keys.add(value)

                        counter[0] += 1

                        if pb is not None:

                            pb.update('chk node', counter[0])

                        yield record

                yield next_stream()

                # Double check that we won't be emitting any keys twice

                next_keys = next_keys.intersection(remaining_keys)

                cur_keys = []

                for prefix in sorted(keys_by_search_prefix):

                    cur_keys.extend(keys_by_search_prefix[prefix])

        for stream in _get_referenced_stream(id_roots):

            yield stream

        for stream in _get_referenced_stream(p_id_roots):

            yield stream

        if remaining_keys:

            trace.note('There were %d keys in the chk index, which were not'

                       ' referenced from inventories', len(remaining_keys))

            stream = source_vf.get_record_stream(remaining_keys, 'unordered',

                                                 True)

            yield stream

    def _execute_pack_operations(self, pack_operations, _packer_class=Packer,

                                 reload_func=None):

        """Execute a series of pack operations.

        :param pack_operations: A list of [revision_count, packs_to_combine].

        :param _packer_class: The class of packer to use (default: Packer).

        :return: None.

        """

        for revision_count, packs in pack_operations:

            # we may have no-ops from the setup logic

            if len(packs) == 0:

                continue

            # Create a new temp VersionedFile instance based on these packs,

            # and then just fetch everything into the target

            to_copy = [('revision_index', 'revisions'),

                       ('inventory_index', 'inventories'),

                       ('text_index', 'texts'),

                       ('signature_index', 'signatures'),

                      ]

            # TODO: This is a very non-optimal ordering for chk_bytes. The

            #       issue is that pages that are similar are not transmitted

            #       together. Perhaps get_record_stream('gc-optimal') should be

            #       taught about how to group chk pages?

            has_chk = False

            if getattr(self, 'chk_index', None) is not None:

                has_chk = True

                to_copy.insert(2, ('chk_index', 'chk_bytes'))

            # Shouldn't we start_write_group around this?

            if self._new_pack is not None:

                raise errors.BzrError('call to %s.pack() while another pack is'

                                      ' being written.'

                                      % (self.__class__.__name__,))

            new_pack = self.pack_factory(self, '.autopack',

                file_mode=self.repo.bzrdir._get_file_mode())

            new_pack.set_write_cache_size(1024*1024)

            # TODO: A better alternative is to probably use Packer.open_pack(), and

            #       then create a GroupCompressVersionedFiles() around the

            #       target pack to insert into.

            pb = ui.ui_factory.nested_progress_bar()

            try:

                for idx, (index_name, vf_name) in enumerate(to_copy):

                    pb.update('repacking %s' % (vf_name,), idx + 1, len(to_copy))

                    keys = set()

                    new_index = getattr(new_pack, index_name)

                    new_index.set_optimize(for_size=True)

                    for pack in packs:

                        source_index = getattr(pack, index_name)

                        keys.update(e[1] for e in source_index.iter_all_entries())

                    trace.mutter('repacking %s with %d keys',

                                 vf_name, len(keys))

                    source_vf = getattr(self.repo, vf_name)

                    target_access = knit._DirectPackAccess({})

                    target_access.set_writer(new_pack._writer, new_index,

                                             new_pack.access_tuple())

                    target_vf = GroupCompressVersionedFiles(

                        _GCGraphIndex(new_index,

                                      add_callback=new_index.add_nodes,

                                      parents=source_vf._index._parents,

                                      is_locked=self.repo.is_locked),

                        access=target_access,

                        delta=source_vf._delta)

                    stream = None

                    child_pb = ui.ui_factory.nested_progress_bar()

                    try:

                        if has_chk:

                            if vf_name == 'inventories':

                                stream, id_roots, p_id_roots = self._get_filtered_inv_stream(

                                    source_vf, keys)

                            elif vf_name == 'chk_bytes':

                                for stream in self._get_chk_stream(source_vf, keys,

                                                    id_roots, p_id_roots,

                                                    pb=child_pb):

                                    target_vf.insert_record_stream(stream)

                                # No more to copy

                                stream = []

                        if stream is None:

                            def pb_stream():

                                substream = source_vf.get_record_stream(keys, 'gc-optimal', True)

                                for idx, record in enumerate(substream):

                                    child_pb.update(vf_name, idx + 1, len(keys))

                                    yield record

                            stream = pb_stream()

                        target_vf.insert_record_stream(stream)

                    finally:

                        child_pb.finished()

                new_pack._check_references() # shouldn't be needed

            except:

                pb.finished()

                new_pack.abort()

                raise

            else:

                pb.finished()

                if not new_pack.data_inserted():

                    raise AssertionError('We copied from pack files,'

                                         ' but had no data copied')

                    # we need to abort somehow, because we don't want to remove

                    # the other packs

                new_pack.finish()

                self.allocate(new_pack)

            for pack in packs:

                self._remove_pack_from_memory(pack)

        # record the newly available packs and stop advertising the old

        # packs

        self._save_pack_names(clear_obsolete_packs=True)

        # Move the old packs out of the way now they are no longer referenced.

        for revision_count, packs in pack_operations:

            self._obsolete_packs(packs)

class GCPackRepository(KnitPackRepository):

    """GC customisation of KnitPackRepository."""

    # Note: I think the CHK support can be dropped from this class as it's

    # implemented via the GCCHKPackRepository class defined next. IGC 20090301

    def __init__(self, _format, a_bzrdir, control_files, _commit_builder_class,

        _serializer):

        """Overridden to change pack collection class."""

        KnitPackRepository.__init__(self, _format, a_bzrdir, control_files,

            _commit_builder_class, _serializer)

        # and now replace everything it did :)

        index_transport = self._transport.clone('indices')

        if chk_support:

            self._pack_collection = GCRepositoryPackCollection(self,

                self._transport, index_transport,

                self._transport.clone('upload'),

                self._transport.clone('packs'),

                _format.index_builder_class,

                _format.index_class,

                use_chk_index=self._format.supports_chks,

                )

        else:

            self._pack_collection = GCRepositoryPackCollection(self,

                self._transport, index_transport,

                self._transport.clone('upload'),

                self._transport.clone('packs'),

                _format.index_builder_class,

                _format.index_class)

        self.inventories = GroupCompressVersionedFiles(

            _GCGraphIndex(self._pack_collection.inventory_index.combined_index,

                add_callback=self._pack_collection.inventory_index.add_callback,

                parents=True, is_locked=self.is_locked),

            access=self._pack_collection.inventory_index.data_access)

        self.revisions = GroupCompressVersionedFiles(

            _GCGraphIndex(self._pack_collection.revision_index.combined_index,

                add_callback=self._pack_collection.revision_index.add_callback,

                parents=True, is_locked=self.is_locked),

            access=self._pack_collection.revision_index.data_access,

            delta=False)

        self.signatures = GroupCompressVersionedFiles(

            _GCGraphIndex(self._pack_collection.signature_index.combined_index,

                add_callback=self._pack_collection.signature_index.add_callback,

                parents=False, is_locked=self.is_locked),

            access=self._pack_collection.signature_index.data_access,

            delta=False)

        self.texts = GroupCompressVersionedFiles(

            _GCGraphIndex(self._pack_collection.text_index.combined_index,

                add_callback=self._pack_collection.text_index.add_callback,

                parents=True, is_locked=self.is_locked),

            access=self._pack_collection.text_index.data_access)

        if chk_support and _format.supports_chks:

            # No graph, no compression:- references from chks are between

            # different objects not temporal versions of the same; and without

            # some sort of temporal structure knit compression will just fail.

            self.chk_bytes = GroupCompressVersionedFiles(

                _GCGraphIndex(self._pack_collection.chk_index.combined_index,

                    add_callback=self._pack_collection.chk_index.add_callback,

                    parents=False, is_locked=self.is_locked),

                access=self._pack_collection.chk_index.data_access)

        else:

            self.chk_bytes = None

        # True when the repository object is 'write locked' (as opposed to the

        # physical lock only taken out around changes to the pack-names list.) 

        # Another way to represent this would be a decorator around the control

        # files object that presents logical locks as physical ones - if this

        # gets ugly consider that alternative design. RBC 20071011

        self._write_lock_count = 0

        self._transaction = None

        # for tests

        self._reconcile_does_inventory_gc = True

        self._reconcile_fixes_text_parents = True

        self._reconcile_backsup_inventory = False

        # Note: We cannot unpack a delta that references a text we haven't seen yet.

        #       There are 2 options, work in fulltexts, or require topological

        #       sorting. Using fulltexts is more optimal for local operations,

        #       because the source can be smart about extracting multiple

        #       in-a-row (and sharing strings). Topological is better for

        #       remote, because we access less data.

        self._fetch_order = 'unordered'

        self._fetch_gc_optimal = True

        self._fetch_uses_deltas = False

if chk_support:

    class GCCHKPackRepository(CHKInventoryRepository):

        """GC customisation of CHKInventoryRepository."""

        def __init__(self, _format, a_bzrdir, control_files, _commit_builder_class,

            _serializer):

            """Overridden to change pack collection class."""

            KnitPackRepository.__init__(self, _format, a_bzrdir, control_files,

                _commit_builder_class, _serializer)

            # and now replace everything it did :)

            index_transport = self._transport.clone('indices')

            self._pack_collection = GCRepositoryPackCollection(self,

                self._transport, index_transport,

                self._transport.clone('upload'),

                self._transport.clone('packs'),

                _format.index_builder_class,

                _format.index_class,

                use_chk_index=self._format.supports_chks,

                )

            self.inventories = GroupCompressVersionedFiles(

                _GCGraphIndex(self._pack_collection.inventory_index.combined_index,

                    add_callback=self._pack_collection.inventory_index.add_callback,

                    parents=True, is_locked=self.is_locked),

                access=self._pack_collection.inventory_index.data_access)

            self.revisions = GroupCompressVersionedFiles(

                _GCGraphIndex(self._pack_collection.revision_index.combined_index,

                    add_callback=self._pack_collection.revision_index.add_callback,

                    parents=True, is_locked=self.is_locked),

                access=self._pack_collection.revision_index.data_access,

                delta=False)

            self.signatures = GroupCompressVersionedFiles(

                _GCGraphIndex(self._pack_collection.signature_index.combined_index,

                    add_callback=self._pack_collection.signature_index.add_callback,

                    parents=False, is_locked=self.is_locked),

                access=self._pack_collection.signature_index.data_access,

                delta=False)

            self.texts = GroupCompressVersionedFiles(

                _GCGraphIndex(self._pack_collection.text_index.combined_index,

                    add_callback=self._pack_collection.text_index.add_callback,

                    parents=True, is_locked=self.is_locked),

                access=self._pack_collection.text_index.data_access)

            assert _format.supports_chks

            # No parents, individual CHK pages don't have specific ancestry

            self.chk_bytes = GroupCompressVersionedFiles(

                _GCGraphIndex(self._pack_collection.chk_index.combined_index,

                    add_callback=self._pack_collection.chk_index.add_callback,

                    parents=False, is_locked=self.is_locked),

                access=self._pack_collection.chk_index.data_access)

            # True when the repository object is 'write locked' (as opposed to the

            # physical lock only taken out around changes to the pack-names list.)

            # Another way to represent this would be a decorator around the control

            # files object that presents logical locks as physical ones - if this

            # gets ugly consider that alternative design. RBC 20071011

            self._write_lock_count = 0

            self._transaction = None

            # for tests

            self._reconcile_does_inventory_gc = True

            self._reconcile_fixes_text_parents = True

            self._reconcile_backsup_inventory = False

            # Note: We cannot unpack a delta that references a text we haven't

            # seen yet. There are 2 options, work in fulltexts, or require

            # topological sorting. Using fulltexts is more optimal for local

            # operations, because the source can be smart about extracting

            # multiple in-a-row (and sharing strings). Topological is better

            # for remote, because we access less data.

            self._fetch_order = 'unordered'

            self._fetch_gc_optimal = True

            self._fetch_uses_deltas = False

class RepositoryFormatPackGCPlain(RepositoryFormatKnitPack6):

    """A B+Tree index using pack repository."""

    repository_class = GCPackRepository

    rich_root_data = False

    def get_format_string(self):

        """See RepositoryFormat.get_format_string()."""

        return ("Bazaar development format - btree+gc "

            "(needs bzr.dev from 1.13)\n")

    def get_format_description(self):

        """See RepositoryFormat.get_format_description()."""

        return ("Development repository format - btree+groupcompress "

            ", interoperates with pack-0.92\n")

if chk_support:

    class RepositoryFormatPackGCCHK16(RepositoryFormatPackDevelopment5Hash16):

        """A hashed CHK+group compress pack repository."""

        repository_class = GCCHKPackRepository

        rich_root_data = True

        def get_format_string(self):

            """See RepositoryFormat.get_format_string()."""

            return ('Bazaar development format - hash16chk+gc rich-root'

                    ' (needs bzr.dev from 1.13)\n')

        def get_format_description(self):

            """See RepositoryFormat.get_format_description()."""

            return ("Development repository format - hash16chk+groupcompress")

    class RepositoryFormatPackGCCHK255(RepositoryFormatPackDevelopment5Hash255):

        """A hashed CHK+group compress pack repository."""

        repository_class = GCCHKPackRepository

        # Setting this to True causes us to use InterModel1And2, so for now set

        # it to False which uses InterDifferingSerializer. When IM1&2 is

        # removed (as it is in bzr.dev) we can set this back to True.

        rich_root_data = False

        def get_format_string(self):

            """See RepositoryFormat.get_format_string()."""

            return ('Bazaar development format - hash255chk+gc rich-root'

                    ' (needs bzr.dev from 1.13)\n')

        def get_format_description(self):

            """See RepositoryFormat.get_format_description()."""

            return ("Development repository format - hash255chk+groupcompress")

def pack_incompatible(source, target, orig_method=InterPackRepo.is_compatible):

    """Be incompatible with the regular fetch code."""

    formats = (RepositoryFormatPackGCPlain,)

    if chk_support:

        formats = formats + (RepositoryFormatPackGCCHK16,

                             RepositoryFormatPackGCCHK255)

    if isinstance(source._format, formats) or isinstance(target._format, formats):

        return False

    else:

        return orig_method(source, target)

InterPackRepo.is_compatible = staticmethod(pack_incompatible)