revlog: change generaldelta delta parent heuristic
The old generaldelta heuristic was "if p1 (or p2) was closer than the last full text,
use it, otherwise use prev". This was problematic when a repo contained multiple
branches that were very different. If commits to branch A were pushed, and the
last full text was branch B, it would generate a fulltext. Then if branch B was
pushed, it would generate another fulltext. The problem is that the last
fulltext (and delta'ing against `prev` in general) has no correlation with the
contents of the incoming revision, and therefore will always have degenerate
cases.
According to the blame, that algorithm was chosen to minimize the chain length.
Since there is already code that protects against that (the delta-vs-fulltext
code), and since it has been improved since the original generaldelta algorithm
went in (2011), I believe the chain length criteria will still be preserved.
The new algorithm always diffs against p1 (or p2 if it's closer), unless the
resulting delta will fail the delta-vs-fulltext check, in which case we delta
against prev.
Some before and after stats on manifest.d size.
internal large repo
old heuristic - 2.0 GB
new heuristic - 1.2 GB
mozilla-central
old heuristic - 242 MB
new heuristic - 261 MB
The regression in mozilla central is due to the new heuristic choosing p2r as
the delta when it's closer to the tip. Switching the algorithm to always prefer
p1r brings the size back down (242 MB). This is result of the way in which
mozilla does merges and pushes, and the result could easily swing the other
direction in other repos (depending on if they merge X into Y or Y into X), but
will never be as degenerate as before.
I future patch will address the regression by introducing an optional, even more
aggressive delta heuristic which will knock the mozilla manifest size down
dramatically.
#!/usr/bin/env python
#
# checkseclevel - checking section title levels in each online help documents
import sys, os
import optparse
# import from the live mercurial repo
sys.path.insert(0, "..")
# fall back to pure modules if required C extensions are not available
sys.path.append(os.path.join('..', 'mercurial', 'pure'))
from mercurial import demandimport; demandimport.enable()
from mercurial.commands import table
from mercurial.help import helptable
from mercurial import extensions
from mercurial import minirst
_verbose = False
def verbose(msg):
if _verbose:
print msg
def error(msg):
sys.stderr.write('%s\n' % msg)
level2mark = ['"', '=', '-', '.', '#']
reservedmarks = ['"']
mark2level = {}
for m, l in zip(level2mark, xrange(len(level2mark))):
if m not in reservedmarks:
mark2level[m] = l
initlevel_topic = 0
initlevel_cmd = 1
initlevel_ext = 1
initlevel_ext_cmd = 3
def showavailables(initlevel):
error(' available marks and order of them in this help: %s' %
(', '.join(['%r' % (m * 4) for m in level2mark[initlevel + 1:]])))
def checkseclevel(doc, name, initlevel):
verbose('checking "%s"' % name)
blocks, pruned = minirst.parse(doc, 0, ['verbose'])
errorcnt = 0
curlevel = initlevel
for block in blocks:
if block['type'] != 'section':
continue
mark = block['underline']
title = block['lines'][0]
if (mark not in mark2level) or (mark2level[mark] <= initlevel):
error('invalid section mark %r for "%s" of %s' %
(mark * 4, title, name))
showavailables(initlevel)
errorcnt += 1
continue
nextlevel = mark2level[mark]
if curlevel < nextlevel and curlevel + 1 != nextlevel:
error('gap of section level at "%s" of %s' %
(title, name))
showavailables(initlevel)
errorcnt += 1
continue
verbose('appropriate section level for "%s %s"' %
(mark * (nextlevel * 2), title))
curlevel = nextlevel
return errorcnt
def checkcmdtable(cmdtable, namefmt, initlevel):
errorcnt = 0
for k, entry in cmdtable.items():
name = k.split("|")[0].lstrip("^")
if not entry[0].__doc__:
verbose('skip checking %s: no help document' %
(namefmt % name))
continue
errorcnt += checkseclevel(entry[0].__doc__,
namefmt % name,
initlevel)
return errorcnt
def checkhghelps():
errorcnt = 0
for names, sec, doc in helptable:
if callable(doc):
doc = doc()
errorcnt += checkseclevel(doc,
'%s help topic' % names[0],
initlevel_topic)
errorcnt += checkcmdtable(table, '%s command', initlevel_cmd)
for name in sorted(extensions.enabled().keys() +
extensions.disabled().keys()):
mod = extensions.load(None, name, None)
if not mod.__doc__:
verbose('skip checking %s extension: no help document' % name)
continue
errorcnt += checkseclevel(mod.__doc__,
'%s extension' % name,
initlevel_ext)
cmdtable = getattr(mod, 'cmdtable', None)
if cmdtable:
errorcnt += checkcmdtable(cmdtable,
'%s command of ' + name + ' extension',
initlevel_ext_cmd)
return errorcnt
def checkfile(filename, initlevel):
if filename == '-':
filename = 'stdin'
doc = sys.stdin.read()
else:
fp = open(filename)
try:
doc = fp.read()
finally:
fp.close()
verbose('checking input from %s with initlevel %d' %
(filename, initlevel))
return checkseclevel(doc, 'input from %s' % filename, initlevel)
if __name__ == "__main__":
optparser = optparse.OptionParser("""%prog [options]
This checks all help documents of Mercurial (topics, commands,
extensions and commands of them), if no file is specified by --file
option.
""")
optparser.add_option("-v", "--verbose",
help="enable additional output",
action="store_true")
optparser.add_option("-f", "--file",
help="filename to read in (or '-' for stdin)",
action="store", default="")
optparser.add_option("-t", "--topic",
help="parse file as help topic",
action="store_const", dest="initlevel", const=0)
optparser.add_option("-c", "--command",
help="parse file as help of core command",
action="store_const", dest="initlevel", const=1)
optparser.add_option("-e", "--extension",
help="parse file as help of extension",
action="store_const", dest="initlevel", const=1)
optparser.add_option("-C", "--extension-command",
help="parse file as help of extension command",
action="store_const", dest="initlevel", const=3)
optparser.add_option("-l", "--initlevel",
help="set initial section level manually",
action="store", type="int", default=0)
(options, args) = optparser.parse_args()
_verbose = options.verbose
if options.file:
if checkfile(options.file, options.initlevel):
sys.exit(1)
else:
if checkhghelps():
sys.exit(1)