protocol: send application/mercurial-0.2 responses to capable clients
With this commit, the HTTP transport now parses the X-HgProto-<N>
header to determine what media type and compression engine to use for
responses. So far, we only compress responses that are already being
compressed with zlib today (stream response types to specific
commands). We can expand things to cover additional response types
later.
The practical side-effect of this commit is that non-zlib compression
engines will be used if both ends support them. This means if both
ends have zstd support, zstd - not zlib - will be used to compress
data!
When cloning the mozilla-unified repository between a local HTTP
server and client, the benefits of non-zlib compression are quite
noticeable:
engine server CPU (s) client CPU (s) bundle size
zlib (l=6) 174.1 283.2 1,148,547,026
zstd (l=1) 99.2 267.3 1,127,513,841
zstd (l=3) 103.1 266.9 1,018,861,363
zstd (l=7) 128.3 269.7 919,190,278
zstd (l=10) 162.0 - 894,547,179
none 95.3 277.2 4,097,566,064
The default zstd compression level is 3. So if you deploy zstd
capable Mercurial to your clients and servers and CPU time on
your server is dominated by "getbundle" requests (clients cloning
and pulling) - and my experience at Mozilla tells me this is often
the case - this commit could drastically reduce your server-side
CPU usage *and* save on bandwidth costs!
Another benefit of this change is that server operators can install
*any* compression engine. While it isn't enabled by default, the
"none" compression engine can now be used to disable wire protocol
compression completely. Previously, commands like "getbundle" always
zlib compressed output, adding considerable overhead to generating
responses. If you are on a high speed network and your server is under
high load, it might be advantageous to trade bandwidth for CPU.
Although, zstd at level 1 doesn't use that much CPU, so I'm not
convinced that disabling compression wholesale is worthwhile. And, my
data seems to indicate a slow down on the client without compression.
I suspect this is due to a lack of buffering resulting in an increase
in socket read() calls and/or the fact we're transferring an extra 3 GB
of data (parsing HTTP chunked transfer and processing extra TCP packets
can add up). This is definitely worth investigating and optimizing. But
since the "none" compressor isn't enabled by default, I'm inclined to
punt on this issue.
This commit introduces tons of tests. Some of these should arguably
have been implemented on previous commits. But it was difficult to
test without the server functionality in place.
# ancestor.py - generic DAG ancestor algorithm for mercurial
#
# Copyright 2006 Matt Mackall <mpm@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.
from __future__ import absolute_import
import collections
import heapq
from .node import nullrev
def commonancestorsheads(pfunc, *nodes):
"""Returns a set with the heads of all common ancestors of all nodes,
heads(::nodes[0] and ::nodes[1] and ...) .
pfunc must return a list of parent vertices for a given vertex.
"""
if not isinstance(nodes, set):
nodes = set(nodes)
if nullrev in nodes:
return set()
if len(nodes) <= 1:
return nodes
allseen = (1 << len(nodes)) - 1
seen = [0] * (max(nodes) + 1)
for i, n in enumerate(nodes):
seen[n] = 1 << i
poison = 1 << (i + 1)
gca = set()
interesting = len(nodes)
nv = len(seen) - 1
while nv >= 0 and interesting:
v = nv
nv -= 1
if not seen[v]:
continue
sv = seen[v]
if sv < poison:
interesting -= 1
if sv == allseen:
gca.add(v)
sv |= poison
if v in nodes:
# history is linear
return set([v])
if sv < poison:
for p in pfunc(v):
sp = seen[p]
if p == nullrev:
continue
if sp == 0:
seen[p] = sv
interesting += 1
elif sp != sv:
seen[p] |= sv
else:
for p in pfunc(v):
if p == nullrev:
continue
sp = seen[p]
if sp and sp < poison:
interesting -= 1
seen[p] = sv
return gca
def ancestors(pfunc, *orignodes):
"""
Returns the common ancestors of a and b that are furthest from a
root (as measured by longest path).
pfunc must return a list of parent vertices for a given vertex.
"""
def deepest(nodes):
interesting = {}
count = max(nodes) + 1
depth = [0] * count
seen = [0] * count
mapping = []
for (i, n) in enumerate(sorted(nodes)):
depth[n] = 1
b = 1 << i
seen[n] = b
interesting[b] = 1
mapping.append((b, n))
nv = count - 1
while nv >= 0 and len(interesting) > 1:
v = nv
nv -= 1
dv = depth[v]
if dv == 0:
continue
sv = seen[v]
for p in pfunc(v):
if p == nullrev:
continue
dp = depth[p]
nsp = sp = seen[p]
if dp <= dv:
depth[p] = dv + 1
if sp != sv:
interesting[sv] += 1
nsp = seen[p] = sv
if sp:
interesting[sp] -= 1
if interesting[sp] == 0:
del interesting[sp]
elif dv == dp - 1:
nsp = sp | sv
if nsp == sp:
continue
seen[p] = nsp
interesting.setdefault(nsp, 0)
interesting[nsp] += 1
interesting[sp] -= 1
if interesting[sp] == 0:
del interesting[sp]
interesting[sv] -= 1
if interesting[sv] == 0:
del interesting[sv]
if len(interesting) != 1:
return []
k = 0
for i in interesting:
k |= i
return set(n for (i, n) in mapping if k & i)
gca = commonancestorsheads(pfunc, *orignodes)
if len(gca) <= 1:
return gca
return deepest(gca)
class incrementalmissingancestors(object):
'''persistent state used to calculate missing ancestors incrementally
Although similar in spirit to lazyancestors below, this is a separate class
because trying to support contains and missingancestors operations with the
same internal data structures adds needless complexity.'''
def __init__(self, pfunc, bases):
self.bases = set(bases)
if not self.bases:
self.bases.add(nullrev)
self.pfunc = pfunc
def hasbases(self):
'''whether the common set has any non-trivial bases'''
return self.bases and self.bases != set([nullrev])
def addbases(self, newbases):
'''grow the ancestor set by adding new bases'''
self.bases.update(newbases)
def removeancestorsfrom(self, revs):
'''remove all ancestors of bases from the set revs (in place)'''
bases = self.bases
pfunc = self.pfunc
revs.difference_update(bases)
# nullrev is always an ancestor
revs.discard(nullrev)
if not revs:
return
# anything in revs > start is definitely not an ancestor of bases
# revs <= start needs to be investigated
start = max(bases)
keepcount = sum(1 for r in revs if r > start)
if len(revs) == keepcount:
# no revs to consider
return
for curr in xrange(start, min(revs) - 1, -1):
if curr not in bases:
continue
revs.discard(curr)
bases.update(pfunc(curr))
if len(revs) == keepcount:
# no more potential revs to discard
break
def missingancestors(self, revs):
'''return all the ancestors of revs that are not ancestors of self.bases
This may include elements from revs.
Equivalent to the revset (::revs - ::self.bases). Revs are returned in
revision number order, which is a topological order.'''
revsvisit = set(revs)
basesvisit = self.bases
pfunc = self.pfunc
bothvisit = revsvisit.intersection(basesvisit)
revsvisit.difference_update(bothvisit)
if not revsvisit:
return []
start = max(max(revsvisit), max(basesvisit))
# At this point, we hold the invariants that:
# - revsvisit is the set of nodes we know are an ancestor of at least
# one of the nodes in revs
# - basesvisit is the same for bases
# - bothvisit is the set of nodes we know are ancestors of at least one
# of the nodes in revs and one of the nodes in bases. bothvisit and
# revsvisit are mutually exclusive, but bothvisit is a subset of
# basesvisit.
# Now we walk down in reverse topo order, adding parents of nodes
# already visited to the sets while maintaining the invariants. When a
# node is found in both revsvisit and basesvisit, it is removed from
# revsvisit and added to bothvisit. When revsvisit becomes empty, there
# are no more ancestors of revs that aren't also ancestors of bases, so
# exit.
missing = []
for curr in xrange(start, nullrev, -1):
if not revsvisit:
break
if curr in bothvisit:
bothvisit.remove(curr)
# curr's parents might have made it into revsvisit through
# another path
for p in pfunc(curr):
revsvisit.discard(p)
basesvisit.add(p)
bothvisit.add(p)
continue
if curr in revsvisit:
missing.append(curr)
revsvisit.remove(curr)
thisvisit = revsvisit
othervisit = basesvisit
elif curr in basesvisit:
thisvisit = basesvisit
othervisit = revsvisit
else:
# not an ancestor of revs or bases: ignore
continue
for p in pfunc(curr):
if p == nullrev:
pass
elif p in othervisit or p in bothvisit:
# p is implicitly in thisvisit. This means p is or should be
# in bothvisit
revsvisit.discard(p)
basesvisit.add(p)
bothvisit.add(p)
else:
# visit later
thisvisit.add(p)
missing.reverse()
return missing
class lazyancestors(object):
def __init__(self, pfunc, revs, stoprev=0, inclusive=False):
"""Create a new object generating ancestors for the given revs. Does
not generate revs lower than stoprev.
This is computed lazily starting from revs. The object supports
iteration and membership.
cl should be a changelog and revs should be an iterable. inclusive is
a boolean that indicates whether revs should be included. Revs lower
than stoprev will not be generated.
Result does not include the null revision."""
self._parentrevs = pfunc
self._initrevs = revs
self._stoprev = stoprev
self._inclusive = inclusive
# Initialize data structures for __contains__.
# For __contains__, we use a heap rather than a deque because
# (a) it minimizes the number of parentrevs calls made
# (b) it makes the loop termination condition obvious
# Python's heap is a min-heap. Multiply all values by -1 to convert it
# into a max-heap.
self._containsvisit = [-rev for rev in revs]
heapq.heapify(self._containsvisit)
if inclusive:
self._containsseen = set(revs)
else:
self._containsseen = set()
def __nonzero__(self):
"""False if the set is empty, True otherwise."""
try:
next(iter(self))
return True
except StopIteration:
return False
def __iter__(self):
"""Generate the ancestors of _initrevs in reverse topological order.
If inclusive is False, yield a sequence of revision numbers starting
with the parents of each revision in revs, i.e., each revision is *not*
considered an ancestor of itself. Results are in breadth-first order:
parents of each rev in revs, then parents of those, etc.
If inclusive is True, yield all the revs first (ignoring stoprev),
then yield all the ancestors of revs as when inclusive is False.
If an element in revs is an ancestor of a different rev it is not
yielded again."""
seen = set()
revs = self._initrevs
if self._inclusive:
for rev in revs:
yield rev
seen.update(revs)
parentrevs = self._parentrevs
stoprev = self._stoprev
visit = collections.deque(revs)
see = seen.add
schedule = visit.append
while visit:
for parent in parentrevs(visit.popleft()):
if parent >= stoprev and parent not in seen:
schedule(parent)
see(parent)
yield parent
def __contains__(self, target):
"""Test whether target is an ancestor of self._initrevs."""
# Trying to do both __iter__ and __contains__ using the same visit
# heap and seen set is complex enough that it slows down both. Keep
# them separate.
seen = self._containsseen
if target in seen:
return True
parentrevs = self._parentrevs
visit = self._containsvisit
stoprev = self._stoprev
heappop = heapq.heappop
heappush = heapq.heappush
see = seen.add
targetseen = False
while visit and -visit[0] > target and not targetseen:
for parent in parentrevs(-heappop(visit)):
if parent < stoprev or parent in seen:
continue
# We need to make sure we push all parents into the heap so
# that we leave it in a consistent state for future calls.
heappush(visit, -parent)
see(parent)
if parent == target:
targetseen = True
return targetseen