wireprotov2: support response caching
One of the things I've learned from managing VCS servers over the
years is that they are hard to scale. It is well known that some
companies have very beefy (read: very expensive) servers to power
their VCS needs. It is also known that specialized servers for
various VCS exist in order to facilitate scaling servers. (Mercurial
is in this boat.)
One of the aspects that make a VCS server hard to scale is the
high CPU load incurred by constant client clone/pull operations.
To alleviate the scaling pain associated with data retrieval
operations, I want to integrate caching into the Mercurial wire
protocol server as robustly as possible such that servers can
aggressively cache responses and defer as much server load as
possible.
This commit represents the initial implementation of a general
caching layer in wire protocol version 2.
We define a new interface and behavior for a wire protocol cacher
in repository.py. (This is probably where a reviewer should look
first to understand what is going on.)
The bulk of the added code is in wireprotov2server.py, where we
define how a command can opt in to being cached and integrate
caching into command dispatching.
From a very high-level:
* A command can declare itself as cacheable by providing a callable
that can be used to derive a cache key.
* At dispatch time, if a command is cacheable, we attempt to
construct a cacher and use it for serving the request and/or
caching the request.
* The dispatch layer handles the bulk of the business logic for
caching, making cachers mostly "dumb content stores."
* The mechanism for invalidating cached entries (one of the harder
parts about caching in general) is by varying the cache key when
state changes. As such, cachers don't need to be concerned with
cache invalidation.
Initially, we've hooked up support for caching "manifestdata" and
"filedata" commands. These are the simplest to cache, as they should
be immutable over time. Caching of commands related to changeset
data is a bit harder (because cache validation is impacted by
changes to bookmarks, phases, etc). This will be implemented later.
(Strictly speaking, censoring a file should invalidate caches. I've
added an inline TODO to track this edge case.)
To prove it works, this commit implements a test-only extension
providing in-memory caching backed by an lrucachedict. A new test
showing this extension behaving properly is added. FWIW, the
cacher is ~50 lines of code, demonstrating the relative ease with
which a cache can be added to a server.
While the test cacher is not suitable for production workloads, just
for kicks I performed a clone of just the changeset and manifest data
for the mozilla-unified repository. With a fully warmed cache (of just
the manifest data since changeset data is not cached), server-side
CPU usage dropped from ~73s to ~28s. That's pretty significant and
demonstrates the potential that response caching has on server
scalability!
Differential Revision: https://phab.mercurial-scm.org/D4773
# formatter.py - generic output formatting for mercurial
#
# Copyright 2012 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.
"""Generic output formatting for Mercurial
The formatter provides API to show data in various ways. The following
functions should be used in place of ui.write():
- fm.write() for unconditional output
- fm.condwrite() to show some extra data conditionally in plain output
- fm.context() to provide changectx to template output
- fm.data() to provide extra data to JSON or template output
- fm.plain() to show raw text that isn't provided to JSON or template output
To show structured data (e.g. date tuples, dicts, lists), apply fm.format*()
beforehand so the data is converted to the appropriate data type. Use
fm.isplain() if you need to convert or format data conditionally which isn't
supported by the formatter API.
To build nested structure (i.e. a list of dicts), use fm.nested().
See also https://www.mercurial-scm.org/wiki/GenericTemplatingPlan
fm.condwrite() vs 'if cond:':
In most cases, use fm.condwrite() so users can selectively show the data
in template output. If it's costly to build data, use plain 'if cond:' with
fm.write().
fm.nested() vs fm.formatdict() (or fm.formatlist()):
fm.nested() should be used to form a tree structure (a list of dicts of
lists of dicts...) which can be accessed through template keywords, e.g.
"{foo % "{bar % {...}} {baz % {...}}"}". On the other hand, fm.formatdict()
exports a dict-type object to template, which can be accessed by e.g.
"{get(foo, key)}" function.
Doctest helper:
>>> def show(fn, verbose=False, **opts):
... import sys
... from . import ui as uimod
... ui = uimod.ui()
... ui.verbose = verbose
... ui.pushbuffer()
... try:
... return fn(ui, ui.formatter(pycompat.sysbytes(fn.__name__),
... pycompat.byteskwargs(opts)))
... finally:
... print(pycompat.sysstr(ui.popbuffer()), end='')
Basic example:
>>> def files(ui, fm):
... files = [(b'foo', 123, (0, 0)), (b'bar', 456, (1, 0))]
... for f in files:
... fm.startitem()
... fm.write(b'path', b'%s', f[0])
... fm.condwrite(ui.verbose, b'date', b' %s',
... fm.formatdate(f[2], b'%Y-%m-%d %H:%M:%S'))
... fm.data(size=f[1])
... fm.plain(b'\\n')
... fm.end()
>>> show(files)
foo
bar
>>> show(files, verbose=True)
foo 1970-01-01 00:00:00
bar 1970-01-01 00:00:01
>>> show(files, template=b'json')
[
{
"date": [0, 0],
"path": "foo",
"size": 123
},
{
"date": [1, 0],
"path": "bar",
"size": 456
}
]
>>> show(files, template=b'path: {path}\\ndate: {date|rfc3339date}\\n')
path: foo
date: 1970-01-01T00:00:00+00:00
path: bar
date: 1970-01-01T00:00:01+00:00
Nested example:
>>> def subrepos(ui, fm):
... fm.startitem()
... fm.write(b'reponame', b'[%s]\\n', b'baz')
... files(ui, fm.nested(b'files', tmpl=b'{reponame}'))
... fm.end()
>>> show(subrepos)
[baz]
foo
bar
>>> show(subrepos, template=b'{reponame}: {join(files % "{path}", ", ")}\\n')
baz: foo, bar
"""
from __future__ import absolute_import, print_function
import contextlib
import itertools
import os
from .i18n import _
from .node import (
hex,
short,
)
from .thirdparty import (
attr,
)
from . import (
error,
pycompat,
templatefilters,
templatekw,
templater,
templateutil,
util,
)
from .utils import dateutil
pickle = util.pickle
class _nullconverter(object):
'''convert non-primitive data types to be processed by formatter'''
# set to True if context object should be stored as item
storecontext = False
@staticmethod
def wrapnested(data, tmpl, sep):
'''wrap nested data by appropriate type'''
return data
@staticmethod
def formatdate(date, fmt):
'''convert date tuple to appropriate format'''
# timestamp can be float, but the canonical form should be int
ts, tz = date
return (int(ts), tz)
@staticmethod
def formatdict(data, key, value, fmt, sep):
'''convert dict or key-value pairs to appropriate dict format'''
# use plain dict instead of util.sortdict so that data can be
# serialized as a builtin dict in pickle output
return dict(data)
@staticmethod
def formatlist(data, name, fmt, sep):
'''convert iterable to appropriate list format'''
return list(data)
class baseformatter(object):
def __init__(self, ui, topic, opts, converter):
self._ui = ui
self._topic = topic
self._opts = opts
self._converter = converter
self._item = None
# function to convert node to string suitable for this output
self.hexfunc = hex
def __enter__(self):
return self
def __exit__(self, exctype, excvalue, traceback):
if exctype is None:
self.end()
def _showitem(self):
'''show a formatted item once all data is collected'''
def startitem(self):
'''begin an item in the format list'''
if self._item is not None:
self._showitem()
self._item = {}
def formatdate(self, date, fmt='%a %b %d %H:%M:%S %Y %1%2'):
'''convert date tuple to appropriate format'''
return self._converter.formatdate(date, fmt)
def formatdict(self, data, key='key', value='value', fmt=None, sep=' '):
'''convert dict or key-value pairs to appropriate dict format'''
return self._converter.formatdict(data, key, value, fmt, sep)
def formatlist(self, data, name, fmt=None, sep=' '):
'''convert iterable to appropriate list format'''
# name is mandatory argument for now, but it could be optional if
# we have default template keyword, e.g. {item}
return self._converter.formatlist(data, name, fmt, sep)
def context(self, **ctxs):
'''insert context objects to be used to render template keywords'''
ctxs = pycompat.byteskwargs(ctxs)
assert all(k in {'repo', 'ctx', 'fctx'} for k in ctxs)
if self._converter.storecontext:
# populate missing resources in fctx -> ctx -> repo order
if 'fctx' in ctxs and 'ctx' not in ctxs:
ctxs['ctx'] = ctxs['fctx'].changectx()
if 'ctx' in ctxs and 'repo' not in ctxs:
ctxs['repo'] = ctxs['ctx'].repo()
self._item.update(ctxs)
def datahint(self):
'''set of field names to be referenced'''
return set()
def data(self, **data):
'''insert data into item that's not shown in default output'''
data = pycompat.byteskwargs(data)
self._item.update(data)
def write(self, fields, deftext, *fielddata, **opts):
'''do default text output while assigning data to item'''
fieldkeys = fields.split()
assert len(fieldkeys) == len(fielddata)
self._item.update(zip(fieldkeys, fielddata))
def condwrite(self, cond, fields, deftext, *fielddata, **opts):
'''do conditional write (primarily for plain formatter)'''
fieldkeys = fields.split()
assert len(fieldkeys) == len(fielddata)
self._item.update(zip(fieldkeys, fielddata))
def plain(self, text, **opts):
'''show raw text for non-templated mode'''
def isplain(self):
'''check for plain formatter usage'''
return False
def nested(self, field, tmpl=None, sep=''):
'''sub formatter to store nested data in the specified field'''
data = []
self._item[field] = self._converter.wrapnested(data, tmpl, sep)
return _nestedformatter(self._ui, self._converter, data)
def end(self):
'''end output for the formatter'''
if self._item is not None:
self._showitem()
def nullformatter(ui, topic, opts):
'''formatter that prints nothing'''
return baseformatter(ui, topic, opts, converter=_nullconverter)
class _nestedformatter(baseformatter):
'''build sub items and store them in the parent formatter'''
def __init__(self, ui, converter, data):
baseformatter.__init__(self, ui, topic='', opts={}, converter=converter)
self._data = data
def _showitem(self):
self._data.append(self._item)
def _iteritems(data):
'''iterate key-value pairs in stable order'''
if isinstance(data, dict):
return sorted(data.iteritems())
return data
class _plainconverter(object):
'''convert non-primitive data types to text'''
storecontext = False
@staticmethod
def wrapnested(data, tmpl, sep):
raise error.ProgrammingError('plainformatter should never be nested')
@staticmethod
def formatdate(date, fmt):
'''stringify date tuple in the given format'''
return dateutil.datestr(date, fmt)
@staticmethod
def formatdict(data, key, value, fmt, sep):
'''stringify key-value pairs separated by sep'''
prefmt = pycompat.identity
if fmt is None:
fmt = '%s=%s'
prefmt = pycompat.bytestr
return sep.join(fmt % (prefmt(k), prefmt(v))
for k, v in _iteritems(data))
@staticmethod
def formatlist(data, name, fmt, sep):
'''stringify iterable separated by sep'''
prefmt = pycompat.identity
if fmt is None:
fmt = '%s'
prefmt = pycompat.bytestr
return sep.join(fmt % prefmt(e) for e in data)
class plainformatter(baseformatter):
'''the default text output scheme'''
def __init__(self, ui, out, topic, opts):
baseformatter.__init__(self, ui, topic, opts, _plainconverter)
if ui.debugflag:
self.hexfunc = hex
else:
self.hexfunc = short
if ui is out:
self._write = ui.write
else:
self._write = lambda s, **opts: out.write(s)
def startitem(self):
pass
def data(self, **data):
pass
def write(self, fields, deftext, *fielddata, **opts):
self._write(deftext % fielddata, **opts)
def condwrite(self, cond, fields, deftext, *fielddata, **opts):
'''do conditional write'''
if cond:
self._write(deftext % fielddata, **opts)
def plain(self, text, **opts):
self._write(text, **opts)
def isplain(self):
return True
def nested(self, field, tmpl=None, sep=''):
# nested data will be directly written to ui
return self
def end(self):
pass
class debugformatter(baseformatter):
def __init__(self, ui, out, topic, opts):
baseformatter.__init__(self, ui, topic, opts, _nullconverter)
self._out = out
self._out.write("%s = [\n" % self._topic)
def _showitem(self):
self._out.write(' %s,\n' % pycompat.byterepr(self._item))
def end(self):
baseformatter.end(self)
self._out.write("]\n")
class pickleformatter(baseformatter):
def __init__(self, ui, out, topic, opts):
baseformatter.__init__(self, ui, topic, opts, _nullconverter)
self._out = out
self._data = []
def _showitem(self):
self._data.append(self._item)
def end(self):
baseformatter.end(self)
self._out.write(pickle.dumps(self._data))
class jsonformatter(baseformatter):
def __init__(self, ui, out, topic, opts):
baseformatter.__init__(self, ui, topic, opts, _nullconverter)
self._out = out
self._out.write("[")
self._first = True
def _showitem(self):
if self._first:
self._first = False
else:
self._out.write(",")
self._out.write("\n {\n")
first = True
for k, v in sorted(self._item.items()):
if first:
first = False
else:
self._out.write(",\n")
u = templatefilters.json(v, paranoid=False)
self._out.write(' "%s": %s' % (k, u))
self._out.write("\n }")
def end(self):
baseformatter.end(self)
self._out.write("\n]\n")
class _templateconverter(object):
'''convert non-primitive data types to be processed by templater'''
storecontext = True
@staticmethod
def wrapnested(data, tmpl, sep):
'''wrap nested data by templatable type'''
return templateutil.mappinglist(data, tmpl=tmpl, sep=sep)
@staticmethod
def formatdate(date, fmt):
'''return date tuple'''
return templateutil.date(date)
@staticmethod
def formatdict(data, key, value, fmt, sep):
'''build object that can be evaluated as either plain string or dict'''
data = util.sortdict(_iteritems(data))
def f():
yield _plainconverter.formatdict(data, key, value, fmt, sep)
return templateutil.hybriddict(data, key=key, value=value, fmt=fmt,
gen=f)
@staticmethod
def formatlist(data, name, fmt, sep):
'''build object that can be evaluated as either plain string or list'''
data = list(data)
def f():
yield _plainconverter.formatlist(data, name, fmt, sep)
return templateutil.hybridlist(data, name=name, fmt=fmt, gen=f)
class templateformatter(baseformatter):
def __init__(self, ui, out, topic, opts):
baseformatter.__init__(self, ui, topic, opts, _templateconverter)
self._out = out
spec = lookuptemplate(ui, topic, opts.get('template', ''))
self._tref = spec.ref
self._t = loadtemplater(ui, spec, defaults=templatekw.keywords,
resources=templateresources(ui),
cache=templatekw.defaulttempl)
self._parts = templatepartsmap(spec, self._t,
['docheader', 'docfooter', 'separator'])
self._counter = itertools.count()
self._renderitem('docheader', {})
def _showitem(self):
item = self._item.copy()
item['index'] = index = next(self._counter)
if index > 0:
self._renderitem('separator', {})
self._renderitem(self._tref, item)
def _renderitem(self, part, item):
if part not in self._parts:
return
ref = self._parts[part]
self._out.write(self._t.render(ref, item))
@util.propertycache
def _symbolsused(self):
return self._t.symbolsused(self._tref)
def datahint(self):
'''set of field names to be referenced from the template'''
return self._symbolsused[0]
def end(self):
baseformatter.end(self)
self._renderitem('docfooter', {})
@attr.s(frozen=True)
class templatespec(object):
ref = attr.ib()
tmpl = attr.ib()
mapfile = attr.ib()
def lookuptemplate(ui, topic, tmpl):
"""Find the template matching the given -T/--template spec 'tmpl'
'tmpl' can be any of the following:
- a literal template (e.g. '{rev}')
- a map-file name or path (e.g. 'changelog')
- a reference to [templates] in config file
- a path to raw template file
A map file defines a stand-alone template environment. If a map file
selected, all templates defined in the file will be loaded, and the
template matching the given topic will be rendered. Aliases won't be
loaded from user config, but from the map file.
If no map file selected, all templates in [templates] section will be
available as well as aliases in [templatealias].
"""
# looks like a literal template?
if '{' in tmpl:
return templatespec('', tmpl, None)
# perhaps a stock style?
if not os.path.split(tmpl)[0]:
mapname = (templater.templatepath('map-cmdline.' + tmpl)
or templater.templatepath(tmpl))
if mapname and os.path.isfile(mapname):
return templatespec(topic, None, mapname)
# perhaps it's a reference to [templates]
if ui.config('templates', tmpl):
return templatespec(tmpl, None, None)
if tmpl == 'list':
ui.write(_("available styles: %s\n") % templater.stylelist())
raise error.Abort(_("specify a template"))
# perhaps it's a path to a map or a template
if ('/' in tmpl or '\\' in tmpl) and os.path.isfile(tmpl):
# is it a mapfile for a style?
if os.path.basename(tmpl).startswith("map-"):
return templatespec(topic, None, os.path.realpath(tmpl))
with util.posixfile(tmpl, 'rb') as f:
tmpl = f.read()
return templatespec('', tmpl, None)
# constant string?
return templatespec('', tmpl, None)
def templatepartsmap(spec, t, partnames):
"""Create a mapping of {part: ref}"""
partsmap = {spec.ref: spec.ref} # initial ref must exist in t
if spec.mapfile:
partsmap.update((p, p) for p in partnames if p in t)
elif spec.ref:
for part in partnames:
ref = '%s:%s' % (spec.ref, part) # select config sub-section
if ref in t:
partsmap[part] = ref
return partsmap
def loadtemplater(ui, spec, defaults=None, resources=None, cache=None):
"""Create a templater from either a literal template or loading from
a map file"""
assert not (spec.tmpl and spec.mapfile)
if spec.mapfile:
frommapfile = templater.templater.frommapfile
return frommapfile(spec.mapfile, defaults=defaults, resources=resources,
cache=cache)
return maketemplater(ui, spec.tmpl, defaults=defaults, resources=resources,
cache=cache)
def maketemplater(ui, tmpl, defaults=None, resources=None, cache=None):
"""Create a templater from a string template 'tmpl'"""
aliases = ui.configitems('templatealias')
t = templater.templater(defaults=defaults, resources=resources,
cache=cache, aliases=aliases)
t.cache.update((k, templater.unquotestring(v))
for k, v in ui.configitems('templates'))
if tmpl:
t.cache[''] = tmpl
return t
# marker to denote a resource to be loaded on demand based on mapping values
# (e.g. (ctx, path) -> fctx)
_placeholder = object()
class templateresources(templater.resourcemapper):
"""Resource mapper designed for the default templatekw and function"""
def __init__(self, ui, repo=None):
self._resmap = {
'cache': {}, # for templatekw/funcs to store reusable data
'repo': repo,
'ui': ui,
}
def availablekeys(self, mapping):
return {k for k in self.knownkeys()
if self._getsome(mapping, k) is not None}
def knownkeys(self):
return {'cache', 'ctx', 'fctx', 'repo', 'revcache', 'ui'}
def lookup(self, mapping, key):
if key not in self.knownkeys():
return None
v = self._getsome(mapping, key)
if v is _placeholder:
v = mapping[key] = self._loadermap[key](self, mapping)
return v
def populatemap(self, context, origmapping, newmapping):
mapping = {}
if self._hasnodespec(newmapping):
mapping['revcache'] = {} # per-ctx cache
if self._hasnodespec(origmapping) and self._hasnodespec(newmapping):
orignode = templateutil.runsymbol(context, origmapping, 'node')
mapping['originalnode'] = orignode
# put marker to override 'ctx'/'fctx' in mapping if any, and flag
# its existence to be reported by availablekeys()
if 'ctx' not in newmapping and self._hasliteral(newmapping, 'node'):
mapping['ctx'] = _placeholder
if 'fctx' not in newmapping and self._hasliteral(newmapping, 'path'):
mapping['fctx'] = _placeholder
return mapping
def _getsome(self, mapping, key):
v = mapping.get(key)
if v is not None:
return v
return self._resmap.get(key)
def _hasliteral(self, mapping, key):
"""Test if a literal value is set or unset in the given mapping"""
return key in mapping and not callable(mapping[key])
def _getliteral(self, mapping, key):
"""Return value of the given name if it is a literal"""
v = mapping.get(key)
if callable(v):
return None
return v
def _hasnodespec(self, mapping):
"""Test if context revision is set or unset in the given mapping"""
return 'node' in mapping or 'ctx' in mapping
def _loadctx(self, mapping):
repo = self._getsome(mapping, 'repo')
node = self._getliteral(mapping, 'node')
if repo is None or node is None:
return
try:
return repo[node]
except error.RepoLookupError:
return None # maybe hidden/non-existent node
def _loadfctx(self, mapping):
ctx = self._getsome(mapping, 'ctx')
path = self._getliteral(mapping, 'path')
if ctx is None or path is None:
return None
try:
return ctx[path]
except error.LookupError:
return None # maybe removed file?
_loadermap = {
'ctx': _loadctx,
'fctx': _loadfctx,
}
def formatter(ui, out, topic, opts):
template = opts.get("template", "")
if template == "json":
return jsonformatter(ui, out, topic, opts)
elif template == "pickle":
return pickleformatter(ui, out, topic, opts)
elif template == "debug":
return debugformatter(ui, out, topic, opts)
elif template != "":
return templateformatter(ui, out, topic, opts)
# developer config: ui.formatdebug
elif ui.configbool('ui', 'formatdebug'):
return debugformatter(ui, out, topic, opts)
# deprecated config: ui.formatjson
elif ui.configbool('ui', 'formatjson'):
return jsonformatter(ui, out, topic, opts)
return plainformatter(ui, out, topic, opts)
@contextlib.contextmanager
def openformatter(ui, filename, topic, opts):
"""Create a formatter that writes outputs to the specified file
Must be invoked using the 'with' statement.
"""
with util.posixfile(filename, 'wb') as out:
with formatter(ui, out, topic, opts) as fm:
yield fm
@contextlib.contextmanager
def _neverending(fm):
yield fm
def maybereopen(fm, filename):
"""Create a formatter backed by file if filename specified, else return
the given formatter
Must be invoked using the 'with' statement. This will never call fm.end()
of the given formatter.
"""
if filename:
return openformatter(fm._ui, filename, fm._topic, fm._opts)
else:
return _neverending(fm)