annotate mercurial/utils/storageutil.py @ 49672:e92de86cf4f8

emitrevision: consider ancestors revision to emit as available base

This should make more delta base valid. This notably affects:

* case where we skipped some parent with empty delta to directly delta against
  an ancestors
* case where an intermediate snapshots is stored.

This change means we could sent largish intermediate snapshots over the wire.
However this is actually a sub goal here. Sending snapshots over the wire means
the client have a high odd of simply storing the pre-computed delta instead of
doing a lengthy process that will… end up doing the same intermediate snapshot.

In addition the overall size of snapshot (or any level) is "only" some or the
overall delta size. (0.17% for my mercurial clone, 20% for my clone of Mozilla
try). So Sending them other the wire is unlikely to change large impact on the
bandwidth used.

If we decide that minimising the bandwidth is an explicit goal, we should
introduce new logic to filter-out snapshot as delta. The current code has no
notion explicite of snapshot so far, they just tended to fall into the wobbly
filtering options.

In some cases, this patch can yield large improvement to the bundling time:

    ### data-env-vars.name      = mozilla-try-2019-02-18-zstd-sparse-revlog
      # benchmark.name          = perf-bundle
      # benchmark.variants.revs = last-100000
    before: 68.787066 seconds
    after:  47.552677 seconds (-30.87%)

That translate to large improvement to the pull time :

    ### data-env-vars.name           = mozilla-try-2019-02-18-zstd-sparse-revlog
      # benchmark.name               = pull
      # benchmark.variants.issue6528 = disabled
      # benchmark.variants.revs      = last-100000
    before: 142.186625 seconds
    after:   75.897745 seconds  (-46.62%)

No significant negative impact have been observed.

# storageutil.py - Storage functionality agnostic of backend implementation.
#
# Copyright 2018 Gregory Szorc <[e-mail]>
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.


import re
import struct

from ..i18n import _
from ..node import (
    bin,
    nullrev,
    sha1nodeconstants,
)
from .. import (
    dagop,
    error,
    mdiff,
)
from ..interfaces import repository
from ..revlogutils import sidedata as sidedatamod
from ..utils import hashutil

_nullhash = hashutil.sha1(sha1nodeconstants.nullid)

# revision data contains extra metadata not part of the official digest
# Only used in changegroup >= v4.
CG_FLAG_SIDEDATA = 1


def hashrevisionsha1(text, p1, p2):
    """Compute the SHA-1 for revision data and its parents.

    This hash combines both the current file contents and its history
    in a manner that makes it easy to distinguish nodes with the same
    content in the revision graph.
    """
    # As of now, if one of the parent node is null, p2 is null
    if p2 == sha1nodeconstants.nullid:
        # deep copy of a hash is faster than creating one
        s = _nullhash.copy()
        s.update(p1)
    else:
        # none of the parent nodes are nullid
        if p1 < p2:
            a = p1
            b = p2
        else:
            a = p2
            b = p1
        s = hashutil.sha1(a)
        s.update(b)
    s.update(text)
    return s.digest()


METADATA_RE = re.compile(b'\x01\n')


def parsemeta(text):
    """Parse metadata header from revision data.

    Returns a 2-tuple of (metadata, offset), where both can be None if there
    is no metadata.
    """
    # text can be buffer, so we can't use .startswith or .index
    if text[:2] != b'\x01\n':
        return None, None
    s = METADATA_RE.search(text, 2).start()
    mtext = text[2:s]
    meta = {}
    for l in mtext.splitlines():
        k, v = l.split(b': ', 1)
        meta[k] = v
    return meta, s + 2


def packmeta(meta, text):
    """Add metadata to fulltext to produce revision text."""
    keys = sorted(meta)
    metatext = b''.join(b'%s: %s\n' % (k, meta[k]) for k in keys)
    return b'\x01\n%s\x01\n%s' % (metatext, text)


def iscensoredtext(text):
    meta = parsemeta(text)[0]
    return meta and b'censored' in meta


def filtermetadata(text):
    """Extract just the revision data from source text.

    Returns ``text`` unless it has a metadata header, in which case we return
    a new buffer without hte metadata.
    """
    if not text.startswith(b'\x01\n'):
        return text

    offset = text.index(b'\x01\n', 2)
    return text[offset + 2 :]


def filerevisioncopied(store, node):
    """Resolve file revision copy metadata.

    Returns ``False`` if the file has no copy metadata. Otherwise a
    2-tuple of the source filename and node.
    """
    if store.parents(node)[0] != sha1nodeconstants.nullid:
        # When creating a copy or move we set filelog parents to null,
        # because contents are probably unrelated and making a delta
        # would not be useful.
        # Conversely, if filelog p1 is non-null we know
        # there is no copy metadata.
        # In the presence of merges, this reasoning becomes invalid
        # if we reorder parents. See tests/test-issue6528.t.
        return False

    meta = parsemeta(store.revision(node))[0]

    # copy and copyrev occur in pairs. In rare cases due to old bugs,
    # one can occur without the other. So ensure both are present to flag
    # as a copy.
    if meta and b'copy' in meta and b'copyrev' in meta:
        return meta[b'copy'], bin(meta[b'copyrev'])

    return False


def filedataequivalent(store, node, filedata):
    """Determines whether file data is equivalent to a stored node.

    Returns True if the passed file data would hash to the same value
    as a stored revision and False otherwise.

    When a stored revision is censored, filedata must be empty to have
    equivalence.

    When a stored revision has copy metadata, it is ignored as part
    of the compare.
    """

    if filedata.startswith(b'\x01\n'):
        revisiontext = b'\x01\n\x01\n' + filedata
    else:
        revisiontext = filedata

    p1, p2 = store.parents(node)

    computednode = hashrevisionsha1(revisiontext, p1, p2)

    if computednode == node:
        return True

    # Censored files compare against the empty file.
    if store.iscensored(store.rev(node)):
        return filedata == b''

    # Renaming a file produces a different hash, even if the data
    # remains unchanged. Check if that's the case.
    if store.renamed(node):
        return store.read(node) == filedata

    return False


def iterrevs(storelen, start=0, stop=None):
    """Iterate over revision numbers in a store."""
    step = 1

    if stop is not None:
        if start > stop:
            step = -1
        stop += step
        if stop > storelen:
            stop = storelen
    else:
        stop = storelen

    return range(start, stop, step)


def fileidlookup(store, fileid, identifier):
    """Resolve the file node for a value.

    ``store`` is an object implementing the ``ifileindex`` interface.

    ``fileid`` can be:

    * A 20 or 32 byte binary node.
    * An integer revision number
    * A 40 or 64 byte hex node.
    * A bytes that can be parsed as an integer representing a revision number.

    ``identifier`` is used to populate ``error.LookupError`` with an identifier
    for the store.

    Raises ``error.LookupError`` on failure.
    """
    if isinstance(fileid, int):
        try:
            return store.node(fileid)
        except IndexError:
            raise error.LookupError(
                b'%d' % fileid, identifier, _(b'no match found')
            )

    if len(fileid) in (20, 32):
        try:
            store.rev(fileid)
            return fileid
        except error.LookupError:
            pass

    if len(fileid) in (40, 64):
        try:
            rawnode = bin(fileid)
            store.rev(rawnode)
            return rawnode
        except TypeError:
            pass

    try:
        rev = int(fileid)

        if b'%d' % rev != fileid:
            raise ValueError

        try:
            return store.node(rev)
        except (IndexError, TypeError):
            pass
    except (ValueError, OverflowError):
        pass

    raise error.LookupError(fileid, identifier, _(b'no match found'))


def resolvestripinfo(minlinkrev, tiprev, headrevs, linkrevfn, parentrevsfn):
    """Resolve information needed to strip revisions.

    Finds the minimum revision number that must be stripped in order to
    strip ``minlinkrev``.

    Returns a 2-tuple of the minimum revision number to do that and a set
    of all revision numbers that have linkrevs that would be broken
    by that strip.

    ``tiprev`` is the current tip-most revision. It is ``len(store) - 1``.
    ``headrevs`` is an iterable of head revisions.
    ``linkrevfn`` is a callable that receives a revision and returns a linked
    revision.
    ``parentrevsfn`` is a callable that receives a revision number and returns
    an iterable of its parent revision numbers.
    """
    brokenrevs = set()
    strippoint = tiprev + 1

    heads = {}
    futurelargelinkrevs = set()
    for head in headrevs:
        headlinkrev = linkrevfn(head)
        heads[head] = headlinkrev
        if headlinkrev >= minlinkrev:
            futurelargelinkrevs.add(headlinkrev)

    # This algorithm involves walking down the rev graph, starting at the
    # heads. Since the revs are topologically sorted according to linkrev,
    # once all head linkrevs are below the minlink, we know there are
    # no more revs that could have a linkrev greater than minlink.
    # So we can stop walking.
    while futurelargelinkrevs:
        strippoint -= 1
        linkrev = heads.pop(strippoint)

        if linkrev < minlinkrev:
            brokenrevs.add(strippoint)
        else:
            futurelargelinkrevs.remove(linkrev)

        for p in parentrevsfn(strippoint):
            if p != nullrev:
                plinkrev = linkrevfn(p)
                heads[p] = plinkrev
                if plinkrev >= minlinkrev:
                    futurelargelinkrevs.add(plinkrev)

    return strippoint, brokenrevs


def emitrevisions(
    store,
    nodes,
    nodesorder,
    resultcls,
    deltaparentfn=None,
    candeltafn=None,
    rawsizefn=None,
    revdifffn=None,
    flagsfn=None,
    deltamode=repository.CG_DELTAMODE_STD,
    revisiondata=False,
    assumehaveparentrevisions=False,
    sidedata_helpers=None,
    debug_info=None,
):
    """Generic implementation of ifiledata.emitrevisions().

    Emitting revision data is subtly complex. This function attempts to
    encapsulate all the logic for doing so in a backend-agnostic way.

    ``store``
       Object conforming to ``ifilestorage`` interface.

    ``nodes``
       List of revision nodes whose data to emit.

    ``resultcls``
       A type implementing the ``irevisiondelta`` interface that will be
       constructed and returned.

    ``deltaparentfn`` (optional)
       Callable receiving a revision number and returning the revision number
       of a revision that the internal delta is stored against. This delta
       will be preferred over computing a new arbitrary delta.

       If not defined, a delta will always be computed from raw revision
       data.

    ``candeltafn`` (optional)
       Callable receiving a pair of revision numbers that returns a bool
       indicating whether a delta between them can be produced.

       If not defined, it is assumed that any two revisions can delta with
       each other.

    ``rawsizefn`` (optional)
       Callable receiving a revision number and returning the length of the
       ``store.rawdata(rev)``.

       If not defined, ``len(store.rawdata(rev))`` will be called.

    ``revdifffn`` (optional)
       Callable receiving a pair of revision numbers that returns a delta
       between them.

       If not defined, a delta will be computed by invoking mdiff code
       on ``store.revision()`` results.

       Defining this function allows a precomputed or stored delta to be
       used without having to compute on.

    ``flagsfn`` (optional)
       Callable receiving a revision number and returns the integer flags
       value for it. If not defined, flags value will be 0.

    ``deltamode``
       constaint on delta to be sent:
       * CG_DELTAMODE_STD  - normal mode, try to reuse storage deltas,
       * CG_DELTAMODE_PREV - only delta against "prev",
       * CG_DELTAMODE_FULL - only issue full snapshot.

       Whether to send fulltext revisions instead of deltas, if allowed.

    ``nodesorder``
    ``revisiondata``
    ``assumehaveparentrevisions``
    ``sidedata_helpers`` (optional)
        If not None, means that sidedata should be included.
        See `revlogutil.sidedata.get_sidedata_helpers`.

    ``debug_info`
        An optionnal dictionnary to gather information about the bundling
        process (if present, see config: debug.bundling.stats.
    """

    fnode = store.node
    frev = store.rev
    parents = store.parentrevs

    if nodesorder == b'nodes':
        revs = [frev(n) for n in nodes]
    elif nodesorder == b'linear':
        revs = {frev(n) for n in nodes}
        revs = dagop.linearize(revs, store.parentrevs)
    else:  # storage and default
        revs = sorted(frev(n) for n in nodes)

    prevrev = None

    if deltamode == repository.CG_DELTAMODE_PREV or assumehaveparentrevisions:
        prevrev = parents(revs[0])[0]

    # Sets of revs available to delta against.
    emitted = set()
    available = set()
    if assumehaveparentrevisions:
        common_heads = set(p for r in revs for p in parents(r))
        common_heads.difference_update(revs)
        available = store.ancestors(common_heads, inclusive=True)

    def is_usable_base(rev):
        """Is a delta against this revision usable over the wire"""
        if rev == nullrev:
            return False
        return rev in emitted or rev in available

    for rev in revs:
        if rev == nullrev:
            continue

        debug_delta_source = None
        if debug_info is not None:
            debug_info['revision-total'] += 1

        node = fnode(rev)
        p1rev, p2rev = parents(rev)

        if debug_info is not None:
            if p1rev != p2rev and p1rev != nullrev and p2rev != nullrev:
                debug_info['merge-total'] += 1

        if deltaparentfn:
            deltaparentrev = deltaparentfn(rev)
            if debug_info is not None:
                if deltaparentrev == nullrev:
                    debug_info['available-full'] += 1
                else:
                    debug_info['available-delta'] += 1

        else:
            deltaparentrev = nullrev

        # Forced delta against previous mode.
        if deltamode == repository.CG_DELTAMODE_PREV:
            if debug_info is not None:
                debug_delta_source = "prev"
            baserev = prevrev

        # We're instructed to send fulltext. Honor that.
        elif deltamode == repository.CG_DELTAMODE_FULL:
            if debug_info is not None:
                debug_delta_source = "full"
            baserev = nullrev
        # We're instructed to use p1. Honor that
        elif deltamode == repository.CG_DELTAMODE_P1:
            if debug_info is not None:
                debug_delta_source = "p1"
            baserev = p1rev

        # There is a delta in storage. We try to use that because it
        # amounts to effectively copying data from storage and is
        # therefore the fastest.
        elif is_usable_base(deltaparentrev):
            if debug_info is not None:
                debug_delta_source = "storage"
            baserev = deltaparentrev
        else:
            if deltaparentrev != nullrev and debug_info is not None:
                debug_info['denied-base-not-available'] += 1
            # No guarantee the receiver has the delta parent, or Storage has a
            # fulltext revision.
            #
            # We compute a delta on the fly to send over the wire.
            #
            # We start with a try against p1, which in the common case should
            # be close to this revision content.
            #
            # note: we could optimize between p1 and p2 in merges cases.
            elif is_usable_base(p1rev):
                if debug_info is not None:
                    debug_delta_source = "p1"
                baserev = p1rev
            # if p1 was not an option, try p2
            elif is_usable_base(p2rev):
                if debug_info is not None:
                    debug_delta_source = "p2"
                baserev = p2rev
            # Send delta against prev in despair
            #
            # using the closest available ancestors first might be better?
            elif prevrev is not None:
                if debug_info is not None:
                    debug_delta_source = "prev"
                baserev = prevrev
            else:
                if debug_info is not None:
                    debug_delta_source = "full"
                baserev = nullrev

        # But we can't actually use our chosen delta base for whatever
        # reason. Reset to fulltext.
        if (
            baserev != nullrev
            and candeltafn is not None
            and not candeltafn(baserev, rev)
        ):
            if debug_info is not None:
                debug_delta_source = "full"
                debug_info['denied-delta-candeltafn'] += 1
            baserev = nullrev

        revision = None
        delta = None
        baserevisionsize = None

        if revisiondata:
            if store.iscensored(baserev) or store.iscensored(rev):
                try:
                    revision = store.rawdata(node)
                except error.CensoredNodeError as e:
                    if debug_info is not None:
                        debug_delta_source = "full"
                        debug_info['denied-delta-not-available'] += 1
                    revision = e.tombstone

                if baserev != nullrev:
                    if rawsizefn:
                        baserevisionsize = rawsizefn(baserev)
                    else:
                        baserevisionsize = len(store.rawdata(baserev))

            elif (
                baserev == nullrev and deltamode != repository.CG_DELTAMODE_PREV
            ):
                if debug_info is not None:
                    debug_info['computed-delta'] += 1  # close enough
                    debug_info['delta-full'] += 1
                revision = store.rawdata(node)
                emitted.add(rev)
            else:
                if revdifffn:
                    if debug_info is not None:
                        if debug_delta_source == "full":
                            debug_info['computed-delta'] += 1
                            debug_info['delta-full'] += 1
                        elif debug_delta_source == "prev":
                            debug_info['computed-delta'] += 1
                            debug_info['delta-against-prev'] += 1
                        elif debug_delta_source == "p1":
                            debug_info['computed-delta'] += 1
                            debug_info['delta-against-p1'] += 1
                        elif debug_delta_source == "storage":
                            debug_info['reused-storage-delta'] += 1
                        else:
                            assert False, 'unreachable'

                    delta = revdifffn(baserev, rev)
                else:
                    if debug_info is not None:
                        if debug_delta_source == "full":
                            debug_info['computed-delta'] += 1
                            debug_info['delta-full'] += 1
                        elif debug_delta_source == "prev":
                            debug_info['computed-delta'] += 1
                            debug_info['delta-against-prev'] += 1
                        elif debug_delta_source == "p1":
                            debug_info['computed-delta'] += 1
                            debug_info['delta-against-p1'] += 1
                        elif debug_delta_source == "storage":
                            # seem quite unlikelry to happens
                            debug_info['computed-delta'] += 1
                            debug_info['reused-storage-delta'] += 1
                        else:
                            assert False, 'unreachable'
                    delta = mdiff.textdiff(
                        store.rawdata(baserev), store.rawdata(rev)
                    )

                emitted.add(rev)

        serialized_sidedata = None
        sidedata_flags = (0, 0)
        if sidedata_helpers:
            try:
                old_sidedata = store.sidedata(rev)
            except error.CensoredNodeError:
                # skip any potential sidedata of the censored revision
                sidedata = {}
            else:
                sidedata, sidedata_flags = sidedatamod.run_sidedata_helpers(
                    store=store,
                    sidedata_helpers=sidedata_helpers,
                    sidedata=old_sidedata,
                    rev=rev,
                )
            if sidedata:
                serialized_sidedata = sidedatamod.serialize_sidedata(sidedata)

        flags = flagsfn(rev) if flagsfn else 0
        protocol_flags = 0
        if serialized_sidedata:
            # Advertise that sidedata exists to the other side
            protocol_flags |= CG_FLAG_SIDEDATA
            # Computers and removers can return flags to add and/or remove
            flags = flags | sidedata_flags[0] & ~sidedata_flags[1]

        yield resultcls(
            node=node,
            p1node=fnode(p1rev),
            p2node=fnode(p2rev),
            basenode=fnode(baserev),
            flags=flags,
            baserevisionsize=baserevisionsize,
            revision=revision,
            delta=delta,
            sidedata=serialized_sidedata,
            protocol_flags=protocol_flags,
        )

        prevrev = rev


def deltaiscensored(delta, baserev, baselenfn):
    """Determine if a delta represents censored revision data.

    ``baserev`` is the base revision this delta is encoded against.
    ``baselenfn`` is a callable receiving a revision number that resolves the
    length of the revision fulltext.

    Returns a bool indicating if the result of the delta represents a censored
    revision.
    """
    # Fragile heuristic: unless new file meta keys are added alphabetically
    # preceding "censored", all censored revisions are prefixed by
    # "\1\ncensored:". A delta producing such a censored revision must be a
    # full-replacement delta, so we inspect the first and only patch in the
    # delta for this prefix.
    hlen = struct.calcsize(b">lll")
    if len(delta) <= hlen:
        return False

    oldlen = baselenfn(baserev)
    newlen = len(delta) - hlen
    if delta[:hlen] != mdiff.replacediffheader(oldlen, newlen):
        return False

    add = b"\1\ncensored:"
    addlen = len(add)
    return newlen >= addlen and delta[hlen : hlen + addlen] == add