revlog: use existing file handle when reading during _addrevision
_addrevision() may need to read from revlogs as part of computing
deltas. Previously, we would flush existing file handles and open
a new, short-lived file handle to perform the reading.
If we have an existing file handle, it seems logical to reuse it
for reading instead of opening a new file handle. This patch
makes that the new behavior.
After this patch, revlog files are only reopened when adding
revisions if the revlog is switched from inline to non-inline.
On Linux when unbundling a bundle of the mozilla-central repo, this
patch has the following impact on system call counts:
Call Before After Delta
write 827,639 673,390 -154,249
open 700,103 684,089 -16,014
read 74,489 74,489 0
fstat 493,924 461,896 -32,028
close 249,131 233,117 -16,014
stat 242,001 242,001 0
lstat 18,676 18,676 0
lseek 20,268 20,268 0
ioctl 14,652 13,173 -1,479
TOTAL 3,180,758 2,930,679 -250,079
It's worth noting that many of the open() calls fail due to missing
files. That's why there are many more open() calls than close().
Despite the significant system call reduction, this change does not
seem to have a significant performance impact on Linux.
On Windows 10 (not a VM, on a SSD), this patch appears to reduce
unbundle time for mozilla-central from ~960s to ~920s. This isn't
as significant as I was hoping. But a decrease it is nonetheless.
Still, Windows unbundle performance is still >2x slower than Linux.
Despite the lack of significant gains, fewer system calls is fewer
system calls. If nothing else, this will narrow the focus of potential
areas to optimize in the future.
# Since it's not easy to write a test that portably deals
# with files from different users/groups, we cheat a bit by
# monkey-patching some functions in the util module
import os
from mercurial import ui, util, error
hgrc = os.environ['HGRCPATH']
f = open(hgrc)
basehgrc = f.read()
f.close()
def testui(user='foo', group='bar', tusers=(), tgroups=(),
cuser='foo', cgroup='bar', debug=False, silent=False,
report=True):
# user, group => owners of the file
# tusers, tgroups => trusted users/groups
# cuser, cgroup => user/group of the current process
# write a global hgrc with the list of trusted users/groups and
# some setting so that we can be sure it was read
f = open(hgrc, 'w')
f.write(basehgrc)
f.write('\n[paths]\n')
f.write('global = /some/path\n\n')
if tusers or tgroups:
f.write('[trusted]\n')
if tusers:
f.write('users = %s\n' % ', '.join(tusers))
if tgroups:
f.write('groups = %s\n' % ', '.join(tgroups))
f.close()
# override the functions that give names to uids and gids
def username(uid=None):
if uid is None:
return cuser
return user
util.username = username
def groupname(gid=None):
if gid is None:
return 'bar'
return group
util.groupname = groupname
def isowner(st):
return user == cuser
util.isowner = isowner
# try to read everything
#print '# File belongs to user %s, group %s' % (user, group)
#print '# trusted users = %s; trusted groups = %s' % (tusers, tgroups)
kind = ('different', 'same')
who = ('', 'user', 'group', 'user and the group')
trusted = who[(user in tusers) + 2*(group in tgroups)]
if trusted:
trusted = ', but we trust the ' + trusted
print '# %s user, %s group%s' % (kind[user == cuser], kind[group == cgroup],
trusted)
u = ui.ui()
u.setconfig('ui', 'debug', str(bool(debug)))
u.setconfig('ui', 'report_untrusted', str(bool(report)))
u.readconfig('.hg/hgrc')
if silent:
return u
print 'trusted'
for name, path in u.configitems('paths'):
print ' ', name, '=', path
print 'untrusted'
for name, path in u.configitems('paths', untrusted=True):
print '.',
u.config('paths', name) # warning with debug=True
print '.',
u.config('paths', name, untrusted=True) # no warnings
print name, '=', path
print
return u
os.mkdir('repo')
os.chdir('repo')
os.mkdir('.hg')
f = open('.hg/hgrc', 'w')
f.write('[paths]\n')
f.write('local = /another/path\n\n')
f.close()
#print '# Everything is run by user foo, group bar\n'
# same user, same group
testui()
# same user, different group
testui(group='def')
# different user, same group
testui(user='abc')
# ... but we trust the group
testui(user='abc', tgroups=['bar'])
# different user, different group
testui(user='abc', group='def')
# ... but we trust the user
testui(user='abc', group='def', tusers=['abc'])
# ... but we trust the group
testui(user='abc', group='def', tgroups=['def'])
# ... but we trust the user and the group
testui(user='abc', group='def', tusers=['abc'], tgroups=['def'])
# ... but we trust all users
print '# we trust all users'
testui(user='abc', group='def', tusers=['*'])
# ... but we trust all groups
print '# we trust all groups'
testui(user='abc', group='def', tgroups=['*'])
# ... but we trust the whole universe
print '# we trust all users and groups'
testui(user='abc', group='def', tusers=['*'], tgroups=['*'])
# ... check that users and groups are in different namespaces
print "# we don't get confused by users and groups with the same name"
testui(user='abc', group='def', tusers=['def'], tgroups=['abc'])
# ... lists of user names work
print "# list of user names"
testui(user='abc', group='def', tusers=['foo', 'xyz', 'abc', 'bleh'],
tgroups=['bar', 'baz', 'qux'])
# ... lists of group names work
print "# list of group names"
testui(user='abc', group='def', tusers=['foo', 'xyz', 'bleh'],
tgroups=['bar', 'def', 'baz', 'qux'])
print "# Can't figure out the name of the user running this process"
testui(user='abc', group='def', cuser=None)
print "# prints debug warnings"
u = testui(user='abc', group='def', cuser='foo', debug=True)
print "# report_untrusted enabled without debug hides warnings"
u = testui(user='abc', group='def', cuser='foo', report=False)
print "# report_untrusted enabled with debug shows warnings"
u = testui(user='abc', group='def', cuser='foo', debug=True, report=False)
print "# ui.readconfig sections"
filename = 'foobar'
f = open(filename, 'w')
f.write('[foobar]\n')
f.write('baz = quux\n')
f.close()
u.readconfig(filename, sections=['foobar'])
print u.config('foobar', 'baz')
print
print "# read trusted, untrusted, new ui, trusted"
u = ui.ui()
u.setconfig('ui', 'debug', 'on')
u.readconfig(filename)
u2 = u.copy()
def username(uid=None):
return 'foo'
util.username = username
u2.readconfig('.hg/hgrc')
print 'trusted:'
print u2.config('foobar', 'baz')
print 'untrusted:'
print u2.config('foobar', 'baz', untrusted=True)
print
print "# error handling"
def assertraises(f, exc=util.Abort):
try:
f()
except exc as inst:
print 'raised', inst.__class__.__name__
else:
print 'no exception?!'
print "# file doesn't exist"
os.unlink('.hg/hgrc')
assert not os.path.exists('.hg/hgrc')
testui(debug=True, silent=True)
testui(user='abc', group='def', debug=True, silent=True)
print
print "# parse error"
f = open('.hg/hgrc', 'w')
f.write('foo')
f.close()
try:
testui(user='abc', group='def', silent=True)
except error.ParseError as inst:
print inst
try:
testui(debug=True, silent=True)
except error.ParseError as inst:
print inst