# branchmap.py - logic to computes, maintain and stores branchmap for local repo
#
# Copyright 2005-2007 Olivia Mackall <olivia@selenic.com>
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.
import struct
from .node import (
bin,
hex,
nullrev,
)
from . import (
encoding,
error,
obsolete,
pycompat,
scmutil,
util,
)
from .utils import (
repoviewutil,
stringutil,
)
if pycompat.TYPE_CHECKING:
from typing import (
Any,
Callable,
Dict,
Iterable,
List,
Optional,
Set,
Tuple,
Union,
)
from . import localrepo
assert any(
(
Any,
Callable,
Dict,
Iterable,
List,
Optional,
Set,
Tuple,
Union,
localrepo,
)
)
subsettable = repoviewutil.subsettable
calcsize = struct.calcsize
pack_into = struct.pack_into
unpack_from = struct.unpack_from
class BranchMapCache:
"""mapping of filtered views of repo with their branchcache"""
def __init__(self):
self._per_filter = {}
def __getitem__(self, repo):
self.updatecache(repo)
return self._per_filter[repo.filtername]
def updatecache(self, repo):
"""Update the cache for the given filtered view on a repository"""
# This can trigger updates for the caches for subsets of the filtered
# view, e.g. when there is no cache for this filtered view or the cache
# is stale.
cl = repo.changelog
filtername = repo.filtername
bcache = self._per_filter.get(filtername)
if bcache is None or not bcache.validfor(repo):
# cache object missing or cache object stale? Read from disk
bcache = branchcache.fromfile(repo)
revs = []
if bcache is None:
# no (fresh) cache available anymore, perhaps we can re-use
# the cache for a subset, then extend that to add info on missing
# revisions.
subsetname = subsettable.get(filtername)
if subsetname is not None:
subset = repo.filtered(subsetname)
bcache = self[subset].copy()
extrarevs = subset.changelog.filteredrevs - cl.filteredrevs
revs.extend(r for r in extrarevs if r <= bcache.tiprev)
else:
# nothing to fall back on, start empty.
bcache = branchcache(repo)
revs.extend(cl.revs(start=bcache.tiprev + 1))
if revs:
bcache.update(repo, revs)
assert bcache.validfor(repo), filtername
self._per_filter[repo.filtername] = bcache
def replace(self, repo, remotebranchmap):
"""Replace the branchmap cache for a repo with a branch mapping.
This is likely only called during clone with a branch map from a
remote.
"""
cl = repo.changelog
clrev = cl.rev
clbranchinfo = cl.branchinfo
rbheads = []
closed = set()
for bheads in remotebranchmap.values():
rbheads += bheads
for h in bheads:
r = clrev(h)
b, c = clbranchinfo(r)
if c:
closed.add(h)
if rbheads:
rtiprev = max((int(clrev(node)) for node in rbheads))
cache = branchcache(
repo,
remotebranchmap,
repo[rtiprev].node(),
rtiprev,
closednodes=closed,
)
# Try to stick it as low as possible
# filter above served are unlikely to be fetch from a clone
for candidate in (b'base', b'immutable', b'served'):
rview = repo.filtered(candidate)
if cache.validfor(rview):
self._per_filter[candidate] = cache
cache.write(rview)
return
def clear(self):
self._per_filter.clear()
def write_delayed(self, repo):
unfi = repo.unfiltered()
for filtername, cache in self._per_filter.items():
if cache._delayed:
repo = unfi.filtered(filtername)
cache.write(repo)
def _unknownnode(node):
"""raises ValueError when branchcache found a node which does not exists"""
raise ValueError('node %s does not exist' % pycompat.sysstr(hex(node)))
def _branchcachedesc(repo):
if repo.filtername is not None:
return b'branch cache (%s)' % repo.filtername
else:
return b'branch cache'
class branchcache:
"""A dict like object that hold branches heads cache.
This cache is used to avoid costly computations to determine all the
branch heads of a repo.
The cache is serialized on disk in the following format:
<tip hex node> <tip rev number> [optional filtered repo hex hash]
<branch head hex node> <open/closed state> <branch name>
<branch head hex node> <open/closed state> <branch name>
...
The first line is used to check if the cache is still valid. If the
branch cache is for a filtered repo view, an optional third hash is
included that hashes the hashes of all filtered and obsolete revisions.
The open/closed state is represented by a single letter 'o' or 'c'.
This field can be used to avoid changelog reads when determining if a
branch head closes a branch or not.
"""
def __init__(
self,
repo,
entries=(),
tipnode=None,
tiprev=nullrev,
filteredhash=None,
closednodes=None,
hasnode=None,
):
# type: (localrepo.localrepository, Union[Dict[bytes, List[bytes]], Iterable[Tuple[bytes, List[bytes]]]], bytes, int, Optional[bytes], Optional[Set[bytes]], Optional[Callable[[bytes], bool]]) -> None
"""hasnode is a function which can be used to verify whether changelog
has a given node or not. If it's not provided, we assume that every node
we have exists in changelog"""
self._repo = repo
self._delayed = False
if tipnode is None:
self.tipnode = repo.nullid
else:
self.tipnode = tipnode
self.tiprev = tiprev
self.filteredhash = filteredhash
# closednodes is a set of nodes that close their branch. If the branch
# cache has been updated, it may contain nodes that are no longer
# heads.
if closednodes is None:
self._closednodes = set()
else:
self._closednodes = closednodes
self._entries = dict(entries)
# whether closed nodes are verified or not
self._closedverified = False
# branches for which nodes are verified
self._verifiedbranches = set()
self._hasnode = hasnode
if self._hasnode is None:
self._hasnode = lambda x: True
def _verifyclosed(self):
"""verify the closed nodes we have"""
if self._closedverified:
return
for node in self._closednodes:
if not self._hasnode(node):
_unknownnode(node)
self._closedverified = True
def _verifybranch(self, branch):
"""verify head nodes for the given branch."""
if branch not in self._entries or branch in self._verifiedbranches:
return
for n in self._entries[branch]:
if not self._hasnode(n):
_unknownnode(n)
self._verifiedbranches.add(branch)
def _verifyall(self):
"""verifies nodes of all the branches"""
needverification = set(self._entries.keys()) - self._verifiedbranches
for b in needverification:
self._verifybranch(b)
def __iter__(self):
return iter(self._entries)
def __setitem__(self, key, value):
self._entries[key] = value
def __getitem__(self, key):
self._verifybranch(key)
return self._entries[key]
def __contains__(self, key):
self._verifybranch(key)
return key in self._entries
def iteritems(self):
for k, v in self._entries.items():
self._verifybranch(k)
yield k, v
items = iteritems
def hasbranch(self, label):
"""checks whether a branch of this name exists or not"""
self._verifybranch(label)
return label in self._entries
@classmethod
def fromfile(cls, repo):
f = None
try:
f = repo.cachevfs(cls._filename(repo))
lineiter = iter(f)
cachekey = next(lineiter).rstrip(b'\n').split(b" ", 2)
last, lrev = cachekey[:2]
last, lrev = bin(last), int(lrev)
filteredhash = None
hasnode = repo.changelog.hasnode
if len(cachekey) > 2:
filteredhash = bin(cachekey[2])
bcache = cls(
repo,
tipnode=last,
tiprev=lrev,
filteredhash=filteredhash,
hasnode=hasnode,
)
if not bcache.validfor(repo):
# invalidate the cache
raise ValueError('tip differs')
bcache.load(repo, lineiter)
except (IOError, OSError):
return None
except Exception as inst:
if repo.ui.debugflag:
msg = b'invalid %s: %s\n'
repo.ui.debug(
msg
% (
_branchcachedesc(repo),
stringutil.forcebytestr(inst),
)
)
bcache = None
finally:
if f:
f.close()
return bcache
def load(self, repo, lineiter):
"""fully loads the branchcache by reading from the file using the line
iterator passed"""
for line in lineiter:
line = line.rstrip(b'\n')
if not line:
continue
node, state, label = line.split(b" ", 2)
if state not in b'oc':
raise ValueError('invalid branch state')
label = encoding.tolocal(label.strip())
node = bin(node)
self._entries.setdefault(label, []).append(node)
if state == b'c':
self._closednodes.add(node)
@staticmethod
def _filename(repo):
"""name of a branchcache file for a given repo or repoview"""
filename = b"branch2"
if repo.filtername:
filename = b'%s-%s' % (filename, repo.filtername)
return filename
def validfor(self, repo):
"""check that cache contents are valid for (a subset of) this repo
- False when the order of changesets changed or if we detect a strip.
- True when cache is up-to-date for the current repo or its subset."""
try:
node = repo.changelog.node(self.tiprev)
except IndexError:
# changesets were stripped and now we don't even have enough to
# find tiprev
return False
if self.tipnode != node:
# tiprev doesn't correspond to tipnode: repo was stripped, or this
# repo has a different order of changesets
return False
tiphash = scmutil.filteredhash(repo, self.tiprev, needobsolete=True)
# hashes don't match if this repo view has a different set of filtered
# revisions (e.g. due to phase changes) or obsolete revisions (e.g.
# history was rewritten)
return self.filteredhash == tiphash
def _branchtip(self, heads):
"""Return tuple with last open head in heads and false,
otherwise return last closed head and true."""
tip = heads[-1]
closed = True
for h in reversed(heads):
if h not in self._closednodes:
tip = h
closed = False
break
return tip, closed
def branchtip(self, branch):
"""Return the tipmost open head on branch head, otherwise return the
tipmost closed head on branch.
Raise KeyError for unknown branch."""
return self._branchtip(self[branch])[0]
def iteropen(self, nodes):
return (n for n in nodes if n not in self._closednodes)
def branchheads(self, branch, closed=False):
self._verifybranch(branch)
heads = self._entries[branch]
if not closed:
heads = list(self.iteropen(heads))
return heads
def iterbranches(self):
for bn, heads in self.items():
yield (bn, heads) + self._branchtip(heads)
def iterheads(self):
"""returns all the heads"""
self._verifyall()
return self._entries.values()
def copy(self):
"""return an deep copy of the branchcache object"""
return type(self)(
self._repo,
self._entries,
self.tipnode,
self.tiprev,
self.filteredhash,
self._closednodes,
)
def write(self, repo):
tr = repo.currenttransaction()
if not getattr(tr, 'finalized', True):
# Avoid premature writing.
#
# (The cache warming setup by localrepo will update the file later.)
self._delayed = True
return
try:
filename = self._filename(repo)
with repo.cachevfs(filename, b"w", atomictemp=True) as f:
cachekey = [hex(self.tipnode), b'%d' % self.tiprev]
if self.filteredhash is not None:
cachekey.append(hex(self.filteredhash))
f.write(b" ".join(cachekey) + b'\n')
nodecount = 0
for label, nodes in sorted(self._entries.items()):
label = encoding.fromlocal(label)
for node in nodes:
nodecount += 1
if node in self._closednodes:
state = b'c'
else:
state = b'o'
f.write(b"%s %s %s\n" % (hex(node), state, label))
repo.ui.log(
b'branchcache',
b'wrote %s with %d labels and %d nodes\n',
_branchcachedesc(repo),
len(self._entries),
nodecount,
)
self._delayed = False
except (IOError, OSError, error.Abort) as inst:
# Abort may be raised by read only opener, so log and continue
repo.ui.debug(
b"couldn't write branch cache: %s\n"
% stringutil.forcebytestr(inst)
)
def update(self, repo, revgen):
"""Given a branchhead cache, self, that may have extra nodes or be
missing heads, and a generator of nodes that are strictly a superset of
heads missing, this function updates self to be correct.
"""
starttime = util.timer()
cl = repo.changelog
# collect new branch entries
newbranches = {}
getbranchinfo = repo.revbranchcache().branchinfo
for r in revgen:
branch, closesbranch = getbranchinfo(r)
newbranches.setdefault(branch, []).append(r)
if closesbranch:
self._closednodes.add(cl.node(r))
# new tip revision which we found after iterating items from new
# branches
ntiprev = self.tiprev
# Delay fetching the topological heads until they are needed.
# A repository without non-continous branches can skip this part.
topoheads = None
# If a changeset is visible, its parents must be visible too, so
# use the faster unfiltered parent accessor.
parentrevs = repo.unfiltered().changelog.parentrevs
# Faster than using ctx.obsolete()
obsrevs = obsolete.getrevs(repo, b'obsolete')
for branch, newheadrevs in newbranches.items():
# For every branch, compute the new branchheads.
# A branchhead is a revision such that no descendant is on
# the same branch.
#
# The branchheads are computed iteratively in revision order.
# This ensures topological order, i.e. parents are processed
# before their children. Ancestors are inclusive here, i.e.
# any revision is an ancestor of itself.
#
# Core observations:
# - The current revision is always a branchhead for the
# repository up to that point.
# - It is the first revision of the branch if and only if
# there was no branchhead before. In that case, it is the
# only branchhead as there are no possible ancestors on
# the same branch.
# - If a parent is on the same branch, a branchhead can
# only be an ancestor of that parent, if it is parent
# itself. Otherwise it would have been removed as ancestor
# of that parent before.
# - Therefore, if all parents are on the same branch, they
# can just be removed from the branchhead set.
# - If one parent is on the same branch and the other is not
# and there was exactly one branchhead known, the existing
# branchhead can only be an ancestor if it is the parent.
# Otherwise it would have been removed as ancestor of
# the parent before. The other parent therefore can't have
# a branchhead as ancestor.
# - In all other cases, the parents on different branches
# could have a branchhead as ancestor. Those parents are
# kept in the "uncertain" set. If all branchheads are also
# topological heads, they can't have descendants and further
# checks can be skipped. Otherwise, the ancestors of the
# "uncertain" set are removed from branchheads.
# This computation is heavy and avoided if at all possible.
bheads = self._entries.get(branch, [])
bheadset = {cl.rev(node) for node in bheads}
uncertain = set()
for newrev in sorted(newheadrevs):
if newrev in obsrevs:
# We ignore obsolete changesets as they shouldn't be
# considered heads.
continue
if not bheadset:
bheadset.add(newrev)
continue
parents = [p for p in parentrevs(newrev) if p != nullrev]
samebranch = set()
otherbranch = set()
obsparents = set()
for p in parents:
if p in obsrevs:
# We ignored this obsolete changeset earlier, but now
# that it has non-ignored children, we need to make
# sure their ancestors are not considered heads. To
# achieve that, we will simply treat this obsolete
# changeset as a parent from other branch.
obsparents.add(p)
elif p in bheadset or getbranchinfo(p)[0] == branch:
samebranch.add(p)
else:
otherbranch.add(p)
if not (len(bheadset) == len(samebranch) == 1):
uncertain.update(otherbranch)
uncertain.update(obsparents)
bheadset.difference_update(samebranch)
bheadset.add(newrev)
if uncertain:
if topoheads is None:
topoheads = set(cl.headrevs())
if bheadset - topoheads:
floorrev = min(bheadset)
if floorrev <= max(uncertain):
ancestors = set(cl.ancestors(uncertain, floorrev))
bheadset -= ancestors
if bheadset:
self[branch] = [cl.node(rev) for rev in sorted(bheadset)]
tiprev = max(newheadrevs)
if tiprev > ntiprev:
ntiprev = tiprev
if ntiprev > self.tiprev:
self.tiprev = ntiprev
self.tipnode = cl.node(ntiprev)
if not self.validfor(repo):
# old cache key is now invalid for the repo, but we've just updated
# the cache and we assume it's valid, so let's make the cache key
# valid as well by recomputing it from the cached data
self.tipnode = repo.nullid
self.tiprev = nullrev
for heads in self.iterheads():
if not heads:
# all revisions on a branch are obsolete
continue
# note: tiprev is not necessarily the tip revision of repo,
# because the tip could be obsolete (i.e. not a head)
tiprev = max(cl.rev(node) for node in heads)
if tiprev > self.tiprev:
self.tipnode = cl.node(tiprev)
self.tiprev = tiprev
self.filteredhash = scmutil.filteredhash(
repo, self.tiprev, needobsolete=True
)
duration = util.timer() - starttime
repo.ui.log(
b'branchcache',
b'updated %s in %.4f seconds\n',
_branchcachedesc(repo),
duration,
)
self.write(repo)
class remotebranchcache(branchcache):
"""Branchmap info for a remote connection, should not write locally"""
def write(self, repo):
pass
# Revision branch info cache
_rbcversion = b'-v1'
_rbcnames = b'rbc-names' + _rbcversion
_rbcrevs = b'rbc-revs' + _rbcversion
# [4 byte hash prefix][4 byte branch name number with sign bit indicating open]
_rbcrecfmt = b'>4sI'
_rbcrecsize = calcsize(_rbcrecfmt)
_rbcmininc = 64 * _rbcrecsize
_rbcnodelen = 4
_rbcbranchidxmask = 0x7FFFFFFF
_rbccloseflag = 0x80000000
class revbranchcache:
"""Persistent cache, mapping from revision number to branch name and close.
This is a low level cache, independent of filtering.
Branch names are stored in rbc-names in internal encoding separated by 0.
rbc-names is append-only, and each branch name is only stored once and will
thus have a unique index.
The branch info for each revision is stored in rbc-revs as constant size
records. The whole file is read into memory, but it is only 'parsed' on
demand. The file is usually append-only but will be truncated if repo
modification is detected.
The record for each revision contains the first 4 bytes of the
corresponding node hash, and the record is only used if it still matches.
Even a completely trashed rbc-revs fill thus still give the right result
while converging towards full recovery ... assuming no incorrectly matching
node hashes.
The record also contains 4 bytes where 31 bits contains the index of the
branch and the last bit indicate that it is a branch close commit.
The usage pattern for rbc-revs is thus somewhat similar to 00changelog.i
and will grow with it but be 1/8th of its size.
"""
def __init__(self, repo, readonly=True):
assert repo.filtername is None
self._repo = repo
self._names = [] # branch names in local encoding with static index
self._rbcrevs = bytearray()
self._rbcsnameslen = 0 # length of names read at _rbcsnameslen
try:
bndata = repo.cachevfs.read(_rbcnames)
self._rbcsnameslen = len(bndata) # for verification before writing
if bndata:
self._names = [
encoding.tolocal(bn) for bn in bndata.split(b'\0')
]
except (IOError, OSError):
if readonly:
# don't try to use cache - fall back to the slow path
self.branchinfo = self._branchinfo
if self._names:
try:
data = repo.cachevfs.read(_rbcrevs)
self._rbcrevs[:] = data
except (IOError, OSError) as inst:
repo.ui.debug(
b"couldn't read revision branch cache: %s\n"
% stringutil.forcebytestr(inst)
)
# remember number of good records on disk
self._rbcrevslen = min(
len(self._rbcrevs) // _rbcrecsize, len(repo.changelog)
)
if self._rbcrevslen == 0:
self._names = []
self._rbcnamescount = len(self._names) # number of names read at
# _rbcsnameslen
def _clear(self):
self._rbcsnameslen = 0
del self._names[:]
self._rbcnamescount = 0
self._rbcrevslen = len(self._repo.changelog)
self._rbcrevs = bytearray(self._rbcrevslen * _rbcrecsize)
util.clearcachedproperty(self, b'_namesreverse')
@util.propertycache
def _namesreverse(self):
return {b: r for r, b in enumerate(self._names)}
def branchinfo(self, rev):
"""Return branch name and close flag for rev, using and updating
persistent cache."""
changelog = self._repo.changelog
rbcrevidx = rev * _rbcrecsize
# avoid negative index, changelog.read(nullrev) is fast without cache
if rev == nullrev:
return changelog.branchinfo(rev)
# if requested rev isn't allocated, grow and cache the rev info
if len(self._rbcrevs) < rbcrevidx + _rbcrecsize:
return self._branchinfo(rev)
# fast path: extract data from cache, use it if node is matching
reponode = changelog.node(rev)[:_rbcnodelen]
cachenode, branchidx = unpack_from(
_rbcrecfmt, util.buffer(self._rbcrevs), rbcrevidx
)
close = bool(branchidx & _rbccloseflag)
if close:
branchidx &= _rbcbranchidxmask
if cachenode == b'\0\0\0\0':
pass
elif cachenode == reponode:
try:
return self._names[branchidx], close
except IndexError:
# recover from invalid reference to unknown branch
self._repo.ui.debug(
b"referenced branch names not found"
b" - rebuilding revision branch cache from scratch\n"
)
self._clear()
else:
# rev/node map has changed, invalidate the cache from here up
self._repo.ui.debug(
b"history modification detected - truncating "
b"revision branch cache to revision %d\n" % rev
)
truncate = rbcrevidx + _rbcrecsize
del self._rbcrevs[truncate:]
self._rbcrevslen = min(self._rbcrevslen, truncate)
# fall back to slow path and make sure it will be written to disk
return self._branchinfo(rev)
def _branchinfo(self, rev):
"""Retrieve branch info from changelog and update _rbcrevs"""
changelog = self._repo.changelog
b, close = changelog.branchinfo(rev)
if b in self._namesreverse:
branchidx = self._namesreverse[b]
else:
branchidx = len(self._names)
self._names.append(b)
self._namesreverse[b] = branchidx
reponode = changelog.node(rev)
if close:
branchidx |= _rbccloseflag
self._setcachedata(rev, reponode, branchidx)
return b, close
def setdata(self, rev, changelogrevision):
"""add new data information to the cache"""
branch, close = changelogrevision.branchinfo
if branch in self._namesreverse:
branchidx = self._namesreverse[branch]
else:
branchidx = len(self._names)
self._names.append(branch)
self._namesreverse[branch] = branchidx
if close:
branchidx |= _rbccloseflag
self._setcachedata(rev, self._repo.changelog.node(rev), branchidx)
# If no cache data were readable (non exists, bad permission, etc)
# the cache was bypassing itself by setting:
#
# self.branchinfo = self._branchinfo
#
# Since we now have data in the cache, we need to drop this bypassing.
if 'branchinfo' in vars(self):
del self.branchinfo
def _setcachedata(self, rev, node, branchidx):
"""Writes the node's branch data to the in-memory cache data."""
if rev == nullrev:
return
rbcrevidx = rev * _rbcrecsize
requiredsize = rbcrevidx + _rbcrecsize
rbccur = len(self._rbcrevs)
if rbccur < requiredsize:
# bytearray doesn't allocate extra space at least in Python 3.7.
# When multiple changesets are added in a row, precise resize would
# result in quadratic complexity. Overallocate to compensate by
# use the classic doubling technique for dynamic arrays instead.
# If there was a gap in the map before, less space will be reserved.
self._rbcrevs.extend(b'\0' * max(_rbcmininc, requiredsize))
pack_into(_rbcrecfmt, self._rbcrevs, rbcrevidx, node, branchidx)
self._rbcrevslen = min(self._rbcrevslen, rev)
tr = self._repo.currenttransaction()
if tr:
tr.addfinalize(b'write-revbranchcache', self.write)
def write(self, tr=None):
"""Save branch cache if it is dirty."""
repo = self._repo
wlock = None
step = b''
try:
# write the new names
if self._rbcnamescount < len(self._names):
wlock = repo.wlock(wait=False)
step = b' names'
self._writenames(repo)
# write the new revs
start = self._rbcrevslen * _rbcrecsize
if start != len(self._rbcrevs):
step = b''
if wlock is None:
wlock = repo.wlock(wait=False)
self._writerevs(repo, start)
except (IOError, OSError, error.Abort, error.LockError) as inst:
repo.ui.debug(
b"couldn't write revision branch cache%s: %s\n"
% (step, stringutil.forcebytestr(inst))
)
finally:
if wlock is not None:
wlock.release()
def _writenames(self, repo):
"""write the new branch names to revbranchcache"""
if self._rbcnamescount != 0:
f = repo.cachevfs.open(_rbcnames, b'ab')
if f.tell() == self._rbcsnameslen:
f.write(b'\0')
else:
f.close()
repo.ui.debug(b"%s changed - rewriting it\n" % _rbcnames)
self._rbcnamescount = 0
self._rbcrevslen = 0
if self._rbcnamescount == 0:
# before rewriting names, make sure references are removed
repo.cachevfs.unlinkpath(_rbcrevs, ignoremissing=True)
f = repo.cachevfs.open(_rbcnames, b'wb')
f.write(
b'\0'.join(
encoding.fromlocal(b)
for b in self._names[self._rbcnamescount :]
)
)
self._rbcsnameslen = f.tell()
f.close()
self._rbcnamescount = len(self._names)
def _writerevs(self, repo, start):
"""write the new revs to revbranchcache"""
revs = min(len(repo.changelog), len(self._rbcrevs) // _rbcrecsize)
with repo.cachevfs.open(_rbcrevs, b'ab') as f:
if f.tell() != start:
repo.ui.debug(
b"truncating cache/%s to %d\n" % (_rbcrevs, start)
)
f.seek(start)
if f.tell() != start:
start = 0
f.seek(start)
f.truncate()
end = revs * _rbcrecsize
f.write(self._rbcrevs[start:end])
self._rbcrevslen = revs