mercurial-scm/hg: mercurial/branchmap.py comparison

comparison mercurial/branchmap.py @ 23785:cb99bacb9b4e

branchcache: introduce revbranchcache for caching of revision branch names It is expensive to retrieve the branch name of a revision. Very expensive when creating a changectx and calling .branch() every time - slightly less when using changelog.branchinfo(). Now, to speed things up, provide a way to cache the results on disk in an efficient format. Each branchname is assigned a number, and for each revision we store the number of the corresponding branch name. The branch names are stored in a dedicated file which is strictly append only. Branch names are usually reused across several revisions, and the total list of branch names will thus be so small that it is feasible to read the whole set of names before using the cache. It will however do that it might be more efficient to use the changelog for retrieving the branch info for a single revision. The revision entries are stored in another file. This file is usually append only, but if the repository has been modified, the file will be truncated and the relevant parts rewritten on demand. The entries for each revision are 8 bytes each, and the whole revision file will thus be 1/8 of 00changelog.i. Each revision entry contains the first 4 bytes of the corresponding node hash. This is used as a check sum that always is verified before the entry is used. That check is relatively expensive but it makes sure history modification is detected and handled correctly. It will also detect and handle most revision file corruptions. This is just a cache. A new format can always be introduced if other requirements or ideas make that seem like a good idea. Rebuilding the cache is not really more expensive than it was to run for example 'hg log -b branchname' before this cache was introduced. This new method is still unused but promise to make some operations several times faster once it actually is used. Abandoning Python 2.4 would make it possible to implement this more efficiently by using struct classes and pack_into. The Python code could probably also be micro optimized or it could be implemented very efficiently in C where it would be easy to control the data access.

author	Mads Kiilerich <madski@unity3d.com>
date	Thu, 08 Jan 2015 00:01:03 +0100
parents	9c3c3dc14a65
children	7d63398fbfd1

comparison

equal deleted inserted replaced

-:8f7e839aaa70
+:cb99bacb9b4e
 from node import bin, hex, nullid, nullrev
 import encoding
 import util
 import time
+from array import array
+from struct import calcsize, pack, unpack
 def _filename(repo):
 """name of a branchcache file for a given repo or repoview"""
 filename = "cache/branch2"
 if repo.filtername:
 self.filteredhash = self._hashfiltered(repo)
 duration = time.time() - starttime
 repo.ui.log('branchcache', 'updated %s branch cache in %.4f seconds\n',
 repo.filtername, duration)
+# Revision branch info cache
+_rbcversion = '-v1'
+_rbcnames = 'cache/rbc-names' + _rbcversion
+_rbcrevs = 'cache/rbc-revs' + _rbcversion
+# [4 byte hash prefix][4 byte branch name number with sign bit indicating open]
+_rbcrecfmt = '>4sI'
+_rbcrecsize = calcsize(_rbcrecfmt)
+_rbcnodelen = 4
+_rbcbranchidxmask = 0x7fffffff
+_rbccloseflag = 0x80000000
+class revbranchcache(object):
+"""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):
+assert repo.filtername is None
+self._names = [] # branch names in local encoding with static index
+self._rbcrevs = array('c') # structs of type _rbcrecfmt
+self._rbcsnameslen = 0
+try:
+bndata = repo.vfs.read(_rbcnames)
+self._rbcsnameslen = len(bndata) # for verification before writing
+self._names = [encoding.tolocal(bn) for bn in bndata.split('\0')]
+except (IOError, OSError), inst:
+repo.ui.debug("couldn't read revision branch cache names: %s\n" %
+inst)
+if self._names:
+try:
+data = repo.vfs.read(_rbcrevs)
+self._rbcrevs.fromstring(data)
+except (IOError, OSError), inst:
+repo.ui.debug("couldn't read revision branch cache: %s\n" %
+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 good names on disk
+self._namesreverse = dict((b, r) for r, b in enumerate(self._names))
+def branchinfo(self, changelog, rev):
+"""Return branch name and close flag for rev, using and updating
+persistent cache."""
+rbcrevidx = rev * _rbcrecsize
+# if requested rev is missing, add and populate all missing revs
+if len(self._rbcrevs) < rbcrevidx + _rbcrecsize:
+first = len(self._rbcrevs) // _rbcrecsize
+self._rbcrevs.extend('\0' * (len(changelog) * _rbcrecsize -
+len(self._rbcrevs)))
+for r in xrange(first, len(changelog)):
+self._branchinfo(r)
+# fast path: extract data from cache, use it if node is matching
+reponode = changelog.node(rev)[:_rbcnodelen]
+cachenode, branchidx = unpack(
+_rbcrecfmt, buffer(self._rbcrevs, rbcrevidx, _rbcrecsize))
+close = bool(branchidx & _rbccloseflag)
+if close:
+branchidx &= _rbcbranchidxmask
+if cachenode == reponode:
+return self._names[branchidx], close
+# fall back to slow path and make sure it will be written to disk
+self._rbcrevslen = min(self._rbcrevslen, rev)
+return self._branchinfo(rev)
+def _branchinfo(self, changelog, rev):
+"""Retrieve branch info from changelog and update _rbcrevs"""
+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
+rbcrevidx = rev * _rbcrecsize
+rec = array('c')
+rec.fromstring(pack(_rbcrecfmt, reponode, branchidx))
+self._rbcrevs[rbcrevidx:rbcrevidx + _rbcrecsize] = rec
+return b, close
+def write(self, repo):
+"""Save branch cache if it is dirty."""
+if self._rbcnamescount < len(self._names):
+try:
+if self._rbcnamescount != 0:
+f = repo.vfs.open(_rbcnames, 'ab')
+if f.tell() == self._rbcsnameslen:
+f.write('\0')
+else:
+f.close()
+self._rbcnamescount = 0
+self._rbcrevslen = 0
+if self._rbcnamescount == 0:
+f = repo.vfs.open(_rbcnames, 'wb')
+f.write('\0'.join(encoding.fromlocal(b)
+for b in self._names[self._rbcnamescount:]))
+self._rbcsnameslen = f.tell()
+f.close()
+except (IOError, OSError, util.Abort), inst:
+repo.ui.debug("couldn't write revision branch cache names: "
+"%s\n" % inst)
+return
+self._rbcnamescount = len(self._names)
+start = self._rbcrevslen * _rbcrecsize
+if start != len(self._rbcrevs):
+self._rbcrevslen = min(len(repo.changelog),
+len(self._rbcrevs) // _rbcrecsize)
+try:
+f = repo.vfs.open(_rbcrevs, 'ab')
+if f.tell() != start:
+f.seek(start)
+f.truncate()
+end = self._rbcrevslen * _rbcrecsize
+f.write(self._rbcrevs[start:end])
+f.close()
+except (IOError, OSError, util.Abort), inst:
+repo.ui.debug("couldn't write revision branch cache: %s\n" %
+inst)
+return

Mercurial > public > mercurial-scm > hg

comparison mercurial/branchmap.py @ 23785:cb99bacb9b4e