revlog: support none compression

revlog files had uncompressed revlog entries support since forever, but
it wasn't selectable or exposed explicitly. It is occassionally useful
for performance testing as it avoids the latency of zlib or zstd. It
also has the nice side effect of providing a non-default compression
engine out-of-the-box.

Differential Revision: https://phab.mercurial-scm.org/D9572

mercurial/utils/compression.py

@@ -1,808 +1,810 b''
 # compression.py - Mercurial utility functions for compression
 #
 # 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, print_function
 
 import bz2
 import collections
 import zlib
 
 from ..pycompat import getattr
 from .. import (
     error,
     i18n,
     pycompat,
 )
 from . import stringutil
 
 safehasattr = pycompat.safehasattr
 
 
 _ = i18n._
 
 # compression code
 
 SERVERROLE = b'server'
 CLIENTROLE = b'client'
 
 compewireprotosupport = collections.namedtuple(
     'compenginewireprotosupport',
     ('name', 'serverpriority', 'clientpriority'),
 )
 
 
 class propertycache(object):
     def __init__(self, func):
         self.func = func
         self.name = func.__name__
 
     def __get__(self, obj, type=None):
         result = self.func(obj)
         self.cachevalue(obj, result)
         return result
 
     def cachevalue(self, obj, value):
         # __dict__ assignment required to bypass __setattr__ (eg: repoview)
         obj.__dict__[self.name] = value
 
 
 class compressormanager(object):
     """Holds registrations of various compression engines.
 
     This class essentially abstracts the differences between compression
     engines to allow new compression formats to be added easily, possibly from
     extensions.
 
     Compressors are registered against the global instance by calling its
     ``register()`` method.
     """
 
     def __init__(self):
         self._engines = {}
         # Bundle spec human name to engine name.
         self._bundlenames = {}
         # Internal bundle identifier to engine name.
         self._bundletypes = {}
         # Revlog header to engine name.
         self._revlogheaders = {}
         # Wire proto identifier to engine name.
         self._wiretypes = {}
 
     def __getitem__(self, key):
         return self._engines[key]
 
     def __contains__(self, key):
         return key in self._engines
 
     def __iter__(self):
         return iter(self._engines.keys())
 
     def register(self, engine):
         """Register a compression engine with the manager.
 
         The argument must be a ``compressionengine`` instance.
         """
         if not isinstance(engine, compressionengine):
             raise ValueError(_(b'argument must be a compressionengine'))
 
         name = engine.name()
 
         if name in self._engines:
             raise error.Abort(
                 _(b'compression engine %s already registered') % name
             )
 
         bundleinfo = engine.bundletype()
         if bundleinfo:
             bundlename, bundletype = bundleinfo
 
             if bundlename in self._bundlenames:
                 raise error.Abort(
                     _(b'bundle name %s already registered') % bundlename
                 )
             if bundletype in self._bundletypes:
                 raise error.Abort(
                     _(b'bundle type %s already registered by %s')
                     % (bundletype, self._bundletypes[bundletype])
                 )
 
             # No external facing name declared.
             if bundlename:
                 self._bundlenames[bundlename] = name
 
             self._bundletypes[bundletype] = name
 
         wiresupport = engine.wireprotosupport()
         if wiresupport:
             wiretype = wiresupport.name
             if wiretype in self._wiretypes:
                 raise error.Abort(
                     _(
                         b'wire protocol compression %s already '
                         b'registered by %s'
                     )
                     % (wiretype, self._wiretypes[wiretype])
                 )
 
             self._wiretypes[wiretype] = name
 
         revlogheader = engine.revlogheader()
         if revlogheader and revlogheader in self._revlogheaders:
             raise error.Abort(
                 _(b'revlog header %s already registered by %s')
                 % (revlogheader, self._revlogheaders[revlogheader])
             )
 
         if revlogheader:
             self._revlogheaders[revlogheader] = name
 
         self._engines[name] = engine
 
     @property
     def supportedbundlenames(self):
         return set(self._bundlenames.keys())
 
     @property
     def supportedbundletypes(self):
         return set(self._bundletypes.keys())
 
     def forbundlename(self, bundlename):
         """Obtain a compression engine registered to a bundle name.
 
         Will raise KeyError if the bundle type isn't registered.
 
         Will abort if the engine is known but not available.
         """
         engine = self._engines[self._bundlenames[bundlename]]
         if not engine.available():
             raise error.Abort(
                 _(b'compression engine %s could not be loaded') % engine.name()
             )
         return engine
 
     def forbundletype(self, bundletype):
         """Obtain a compression engine registered to a bundle type.
 
         Will raise KeyError if the bundle type isn't registered.
 
         Will abort if the engine is known but not available.
         """
         engine = self._engines[self._bundletypes[bundletype]]
         if not engine.available():
             raise error.Abort(
                 _(b'compression engine %s could not be loaded') % engine.name()
             )
         return engine
 
     def supportedwireengines(self, role, onlyavailable=True):
         """Obtain compression engines that support the wire protocol.
 
         Returns a list of engines in prioritized order, most desired first.
 
         If ``onlyavailable`` is set, filter out engines that can't be
         loaded.
         """
         assert role in (SERVERROLE, CLIENTROLE)
 
         attr = b'serverpriority' if role == SERVERROLE else b'clientpriority'
 
         engines = [self._engines[e] for e in self._wiretypes.values()]
         if onlyavailable:
             engines = [e for e in engines if e.available()]
 
         def getkey(e):
             # Sort first by priority, highest first. In case of tie, sort
             # alphabetically. This is arbitrary, but ensures output is
             # stable.
             w = e.wireprotosupport()
             return -1 * getattr(w, attr), w.name
 
         return list(sorted(engines, key=getkey))
 
     def forwiretype(self, wiretype):
         engine = self._engines[self._wiretypes[wiretype]]
         if not engine.available():
             raise error.Abort(
                 _(b'compression engine %s could not be loaded') % engine.name()
             )
         return engine
 
     def forrevlogheader(self, header):
         """Obtain a compression engine registered to a revlog header.
 
         Will raise KeyError if the revlog header value isn't registered.
         """
         return self._engines[self._revlogheaders[header]]
 
 
 compengines = compressormanager()
 
 
 class compressionengine(object):
     """Base class for compression engines.
 
     Compression engines must implement the interface defined by this class.
     """
 
     def name(self):
         """Returns the name of the compression engine.
 
         This is the key the engine is registered under.
 
         This method must be implemented.
         """
         raise NotImplementedError()
 
     def available(self):
         """Whether the compression engine is available.
 
         The intent of this method is to allow optional compression engines
         that may not be available in all installations (such as engines relying
         on C extensions that may not be present).
         """
         return True
 
     def bundletype(self):
         """Describes bundle identifiers for this engine.
 
         If this compression engine isn't supported for bundles, returns None.
 
         If this engine can be used for bundles, returns a 2-tuple of strings of
         the user-facing "bundle spec" compression name and an internal
         identifier used to denote the compression format within bundles. To
         exclude the name from external usage, set the first element to ``None``.
 
         If bundle compression is supported, the class must also implement
         ``compressstream`` and `decompressorreader``.
 
         The docstring of this method is used in the help system to tell users
         about this engine.
         """
         return None
 
     def wireprotosupport(self):
         """Declare support for this compression format on the wire protocol.
 
         If this compression engine isn't supported for compressing wire
         protocol payloads, returns None.
 
         Otherwise, returns ``compenginewireprotosupport`` with the following
         fields:
 
         * String format identifier
         * Integer priority for the server
         * Integer priority for the client
 
         The integer priorities are used to order the advertisement of format
         support by server and client. The highest integer is advertised
         first. Integers with non-positive values aren't advertised.
 
         The priority values are somewhat arbitrary and only used for default
         ordering. The relative order can be changed via config options.
 
         If wire protocol compression is supported, the class must also implement
         ``compressstream`` and ``decompressorreader``.
         """
         return None
 
     def revlogheader(self):
         """Header added to revlog chunks that identifies this engine.
 
         If this engine can be used to compress revlogs, this method should
         return the bytes used to identify chunks compressed with this engine.
         Else, the method should return ``None`` to indicate it does not
         participate in revlog compression.
         """
         return None
 
     def compressstream(self, it, opts=None):
         """Compress an iterator of chunks.
 
         The method receives an iterator (ideally a generator) of chunks of
         bytes to be compressed. It returns an iterator (ideally a generator)
         of bytes of chunks representing the compressed output.
 
         Optionally accepts an argument defining how to perform compression.
         Each engine treats this argument differently.
         """
         raise NotImplementedError()
 
     def decompressorreader(self, fh):
         """Perform decompression on a file object.
 
         Argument is an object with a ``read(size)`` method that returns
         compressed data. Return value is an object with a ``read(size)`` that
         returns uncompressed data.
         """
         raise NotImplementedError()
 
     def revlogcompressor(self, opts=None):
         """Obtain an object that can be used to compress revlog entries.
 
         The object has a ``compress(data)`` method that compresses binary
         data. This method returns compressed binary data or ``None`` if
         the data could not be compressed (too small, not compressible, etc).
         The returned data should have a header uniquely identifying this
         compression format so decompression can be routed to this engine.
         This header should be identified by the ``revlogheader()`` return
         value.
 
         The object has a ``decompress(data)`` method that decompresses
         data. The method will only be called if ``data`` begins with
         ``revlogheader()``. The method should return the raw, uncompressed
         data or raise a ``StorageError``.
 
         The object is reusable but is not thread safe.
         """
         raise NotImplementedError()
 
 
 class _CompressedStreamReader(object):
     def __init__(self, fh):
         if safehasattr(fh, 'unbufferedread'):
             self._reader = fh.unbufferedread
         else:
             self._reader = fh.read
         self._pending = []
         self._pos = 0
         self._eof = False
 
     def _decompress(self, chunk):
         raise NotImplementedError()
 
     def read(self, l):
         buf = []
         while True:
             while self._pending:
                 if len(self._pending[0]) > l + self._pos:
                     newbuf = self._pending[0]
                     buf.append(newbuf[self._pos : self._pos + l])
                     self._pos += l
                     return b''.join(buf)
 
                 newbuf = self._pending.pop(0)
                 if self._pos:
                     buf.append(newbuf[self._pos :])
                     l -= len(newbuf) - self._pos
                 else:
                     buf.append(newbuf)
                     l -= len(newbuf)
                 self._pos = 0
 
             if self._eof:
                 return b''.join(buf)
             chunk = self._reader(65536)
             self._decompress(chunk)
             if not chunk and not self._pending and not self._eof:
                 # No progress and no new data, bail out
                 return b''.join(buf)
 
 
 class _GzipCompressedStreamReader(_CompressedStreamReader):
     def __init__(self, fh):
         super(_GzipCompressedStreamReader, self).__init__(fh)
         self._decompobj = zlib.decompressobj()
 
     def _decompress(self, chunk):
         newbuf = self._decompobj.decompress(chunk)
         if newbuf:
             self._pending.append(newbuf)
         d = self._decompobj.copy()
         try:
             d.decompress(b'x')
             d.flush()
             if d.unused_data == b'x':
                 self._eof = True
         except zlib.error:
             pass
 
 
 class _BZ2CompressedStreamReader(_CompressedStreamReader):
     def __init__(self, fh):
         super(_BZ2CompressedStreamReader, self).__init__(fh)
         self._decompobj = bz2.BZ2Decompressor()
 
     def _decompress(self, chunk):
         newbuf = self._decompobj.decompress(chunk)
         if newbuf:
             self._pending.append(newbuf)
         try:
             while True:
                 newbuf = self._decompobj.decompress(b'')
                 if newbuf:
                     self._pending.append(newbuf)
                 else:
                     break
         except EOFError:
             self._eof = True
 
 
 class _TruncatedBZ2CompressedStreamReader(_BZ2CompressedStreamReader):
     def __init__(self, fh):
         super(_TruncatedBZ2CompressedStreamReader, self).__init__(fh)
         newbuf = self._decompobj.decompress(b'BZ')
         if newbuf:
             self._pending.append(newbuf)
 
 
 class _ZstdCompressedStreamReader(_CompressedStreamReader):
     def __init__(self, fh, zstd):
         super(_ZstdCompressedStreamReader, self).__init__(fh)
         self._zstd = zstd
         self._decompobj = zstd.ZstdDecompressor().decompressobj()
 
     def _decompress(self, chunk):
         newbuf = self._decompobj.decompress(chunk)
         if newbuf:
             self._pending.append(newbuf)
         try:
             while True:
                 newbuf = self._decompobj.decompress(b'')
                 if newbuf:
                     self._pending.append(newbuf)
                 else:
                     break
         except self._zstd.ZstdError:
             self._eof = True
 
 
 class _zlibengine(compressionengine):
     def name(self):
         return b'zlib'
 
     def bundletype(self):
         """zlib compression using the DEFLATE algorithm.
 
         All Mercurial clients should support this format. The compression
         algorithm strikes a reasonable balance between compression ratio
         and size.
         """
         return b'gzip', b'GZ'
 
     def wireprotosupport(self):
         return compewireprotosupport(b'zlib', 20, 20)
 
     def revlogheader(self):
         return b'x'
 
     def compressstream(self, it, opts=None):
         opts = opts or {}
 
         z = zlib.compressobj(opts.get(b'level', -1))
         for chunk in it:
             data = z.compress(chunk)
             # Not all calls to compress emit data. It is cheaper to inspect
             # here than to feed empty chunks through generator.
             if data:
                 yield data
 
         yield z.flush()
 
     def decompressorreader(self, fh):
         return _GzipCompressedStreamReader(fh)
 
     class zlibrevlogcompressor(object):
         def __init__(self, level=None):
             self._level = level
 
         def compress(self, data):
             insize = len(data)
             # Caller handles empty input case.
             assert insize > 0
 
             if insize < 44:
                 return None
 
             elif insize <= 1000000:
                 if self._level is None:
                     compressed = zlib.compress(data)
                 else:
                     compressed = zlib.compress(data, self._level)
                 if len(compressed) < insize:
                     return compressed
                 return None
 
             # zlib makes an internal copy of the input buffer, doubling
             # memory usage for large inputs. So do streaming compression
             # on large inputs.
             else:
                 if self._level is None:
                     z = zlib.compressobj()
                 else:
                     z = zlib.compressobj(level=self._level)
                 parts = []
                 pos = 0
                 while pos < insize:
                     pos2 = pos + 2 ** 20
                     parts.append(z.compress(data[pos:pos2]))
                     pos = pos2
                 parts.append(z.flush())
 
                 if sum(map(len, parts)) < insize:
                     return b''.join(parts)
                 return None
 
         def decompress(self, data):
             try:
                 return zlib.decompress(data)
             except zlib.error as e:
                 raise error.StorageError(
                     _(b'revlog decompress error: %s')
                     % stringutil.forcebytestr(e)
                 )
 
     def revlogcompressor(self, opts=None):
         level = None
         if opts is not None:
             level = opts.get(b'zlib.level')
         return self.zlibrevlogcompressor(level)
 
 
 compengines.register(_zlibengine())
 
 
 class _bz2engine(compressionengine):
     def name(self):
         return b'bz2'
 
     def bundletype(self):
         """An algorithm that produces smaller bundles than ``gzip``.
 
         All Mercurial clients should support this format.
 
         This engine will likely produce smaller bundles than ``gzip`` but
         will be significantly slower, both during compression and
         decompression.
 
         If available, the ``zstd`` engine can yield similar or better
         compression at much higher speeds.
         """
         return b'bzip2', b'BZ'
 
     # We declare a protocol name but don't advertise by default because
     # it is slow.
     def wireprotosupport(self):
         return compewireprotosupport(b'bzip2', 0, 0)
 
     def compressstream(self, it, opts=None):
         opts = opts or {}
         z = bz2.BZ2Compressor(opts.get(b'level', 9))
         for chunk in it:
             data = z.compress(chunk)
             if data:
                 yield data
 
         yield z.flush()
 
     def decompressorreader(self, fh):
         return _BZ2CompressedStreamReader(fh)
 
 
 compengines.register(_bz2engine())
 
 
 class _truncatedbz2engine(compressionengine):
     def name(self):
         return b'bz2truncated'
 
     def bundletype(self):
         return None, b'_truncatedBZ'
 
     # We don't implement compressstream because it is hackily handled elsewhere.
 
     def decompressorreader(self, fh):
         return _TruncatedBZ2CompressedStreamReader(fh)
 
 
 compengines.register(_truncatedbz2engine())
 
 
 class _noopengine(compressionengine):
     def name(self):
         return b'none'
 
     def bundletype(self):
         """No compression is performed.
 
         Use this compression engine to explicitly disable compression.
         """
         return b'none', b'UN'
 
     # Clients always support uncompressed payloads. Servers don't because
     # unless you are on a fast network, uncompressed payloads can easily
     # saturate your network pipe.
     def wireprotosupport(self):
         return compewireprotosupport(b'none', 0, 10)
 
-    # We don't implement revlogheader because it is handled specially
-    # in the revlog class.
+    # revlog special cases the uncompressed case, but implementing
+    # revlogheader allows forcing uncompressed storage.
+    def revlogheader(self):
+        return b'\0'
 
     def compressstream(self, it, opts=None):
         return it
 
     def decompressorreader(self, fh):
         return fh
 
     class nooprevlogcompressor(object):
         def compress(self, data):
             return None
 
     def revlogcompressor(self, opts=None):
         return self.nooprevlogcompressor()
 
 
 compengines.register(_noopengine())
 
 
 class _zstdengine(compressionengine):
     def name(self):
         return b'zstd'
 
     @propertycache
     def _module(self):
         # Not all installs have the zstd module available. So defer importing
         # until first access.
         try:
             from .. import zstd  # pytype: disable=import-error
 
             # Force delayed import.
             zstd.__version__
             return zstd
         except ImportError:
             return None
 
     def available(self):
         return bool(self._module)
 
     def bundletype(self):
         """A modern compression algorithm that is fast and highly flexible.
 
         Only supported by Mercurial 4.1 and newer clients.
 
         With the default settings, zstd compression is both faster and yields
         better compression than ``gzip``. It also frequently yields better
         compression than ``bzip2`` while operating at much higher speeds.
 
         If this engine is available and backwards compatibility is not a
         concern, it is likely the best available engine.
         """
         return b'zstd', b'ZS'
 
     def wireprotosupport(self):
         return compewireprotosupport(b'zstd', 50, 50)
 
     def revlogheader(self):
         return b'\x28'
 
     def compressstream(self, it, opts=None):
         opts = opts or {}
         # zstd level 3 is almost always significantly faster than zlib
         # while providing no worse compression. It strikes a good balance
         # between speed and compression.
         level = opts.get(b'level', 3)
 
         zstd = self._module
         z = zstd.ZstdCompressor(level=level).compressobj()
         for chunk in it:
             data = z.compress(chunk)
             if data:
                 yield data
 
         yield z.flush()
 
     def decompressorreader(self, fh):
         return _ZstdCompressedStreamReader(fh, self._module)
 
     class zstdrevlogcompressor(object):
         def __init__(self, zstd, level=3):
             # TODO consider omitting frame magic to save 4 bytes.
             # This writes content sizes into the frame header. That is
             # extra storage. But it allows a correct size memory allocation
             # to hold the result.
             self._cctx = zstd.ZstdCompressor(level=level)
             self._dctx = zstd.ZstdDecompressor()
             self._compinsize = zstd.COMPRESSION_RECOMMENDED_INPUT_SIZE
             self._decompinsize = zstd.DECOMPRESSION_RECOMMENDED_INPUT_SIZE
 
         def compress(self, data):
             insize = len(data)
             # Caller handles empty input case.
             assert insize > 0
 
             if insize < 50:
                 return None
 
             elif insize <= 1000000:
                 compressed = self._cctx.compress(data)
                 if len(compressed) < insize:
                     return compressed
                 return None
             else:
                 z = self._cctx.compressobj()
                 chunks = []
                 pos = 0
                 while pos < insize:
                     pos2 = pos + self._compinsize
                     chunk = z.compress(data[pos:pos2])
                     if chunk:
                         chunks.append(chunk)
                     pos = pos2
                 chunks.append(z.flush())
 
                 if sum(map(len, chunks)) < insize:
                     return b''.join(chunks)
                 return None
 
         def decompress(self, data):
             insize = len(data)
 
             try:
                 # This was measured to be faster than other streaming
                 # decompressors.
                 dobj = self._dctx.decompressobj()
                 chunks = []
                 pos = 0
                 while pos < insize:
                     pos2 = pos + self._decompinsize
                     chunk = dobj.decompress(data[pos:pos2])
                     if chunk:
                         chunks.append(chunk)
                     pos = pos2
                 # Frame should be exhausted, so no finish() API.
 
                 return b''.join(chunks)
             except Exception as e:
                 raise error.StorageError(
                     _(b'revlog decompress error: %s')
                     % stringutil.forcebytestr(e)
                 )
 
     def revlogcompressor(self, opts=None):
         opts = opts or {}
         level = opts.get(b'zstd.level')
         if level is None:
             level = opts.get(b'level')
         if level is None:
             level = 3
         return self.zstdrevlogcompressor(self._module, level=level)
 
 
 compengines.register(_zstdengine())
 
 
 def bundlecompressiontopics():
     """Obtains a list of available bundle compressions for use in help."""
     # help.makeitemsdocs() expects a dict of names to items with a .__doc__.
     items = {}
 
     # We need to format the docstring. So use a dummy object/type to hold it
     # rather than mutating the original.
     class docobject(object):
         pass
 
     for name in compengines:
         engine = compengines[name]
 
         if not engine.available():
             continue
 
         bt = engine.bundletype()
         if not bt or not bt[0]:
             continue
 
         doc = b'``%s``\n    %s' % (bt[0], pycompat.getdoc(engine.bundletype))
 
         value = docobject()
         value.__doc__ = pycompat.sysstr(doc)
         value._origdoc = engine.bundletype.__doc__
         value._origfunc = engine.bundletype
 
         items[bt[0]] = value
 
     return items
 
 
 i18nfunctions = bundlecompressiontopics().values()

tests/test-repo-compengines.t

@@ -1,204 +1,243 b''
 A new repository uses zlib storage, which doesn't need a requirement
 
   $ hg init default
   $ cd default
   $ cat .hg/requires
   dotencode
   fncache
   generaldelta
   revlogv1
   sparserevlog
   store
   testonly-simplestore (reposimplestore !)
 
   $ touch foo
   $ hg -q commit -A -m 'initial commit with a lot of repeated repeated repeated text to trigger compression'
   $ hg debugrevlog -c | grep 0x78
       0x78 (x)  :   1 (100.00%)
       0x78 (x)  : 110 (100.00%)
 
   $ cd ..
 
 Unknown compression engine to format.compression aborts
 
   $ hg --config format.revlog-compression=unknown init unknown
   abort: compression engines "unknown" defined by format.revlog-compression not available
   (run "hg debuginstall" to list available compression engines)
   [255]
 
 unknown compression engine in a list with known one works fine
 
   $ hg --config format.revlog-compression=zlib,unknown init zlib-before-unknow
   $ hg --config format.revlog-compression=unknown,zlib init unknown-before-zlib
 
 A requirement specifying an unknown compression engine results in bail
 
   $ hg init unknownrequirement
   $ cd unknownrequirement
   $ echo exp-compression-unknown >> .hg/requires
   $ hg log
   abort: repository requires features unknown to this Mercurial: exp-compression-unknown
   (see https://mercurial-scm.org/wiki/MissingRequirement for more information)
   [255]
 
   $ cd ..
 
+Specifying a new format.compression on an existing repo won't introduce data
+with that engine or a requirement
+
+  $ cd default
+  $ touch bar
+  $ hg --config format.revlog-compression=none -q commit -A -m 'add bar with a lot of repeated repeated repeated text'
+
+  $ cat .hg/requires
+  dotencode
+  fncache
+  generaldelta
+  revlogv1
+  sparserevlog
+  store
+  testonly-simplestore (reposimplestore !)
+
+  $ hg debugrevlog -c | grep 0x78
+      0x78 (x)  :   2 (100.00%)
+      0x78 (x)  : 199 (100.00%)
+  $ cd ..
+
 #if zstd
 
   $ hg --config format.revlog-compression=zstd init zstd
   $ cd zstd
   $ cat .hg/requires
   dotencode
   fncache
   generaldelta
   revlog-compression-zstd
   revlogv1
   sparserevlog
   store
   testonly-simplestore (reposimplestore !)
 
   $ touch foo
   $ hg -q commit -A -m 'initial commit with a lot of repeated repeated repeated text'
 
   $ hg debugrevlog -c | grep 0x28
       0x28      :  1 (100.00%)
       0x28      : 98 (100.00%)
 
   $ cd ..
 
-Specifying a new format.compression on an existing repo won't introduce data
-with that engine or a requirement
-
-  $ cd default
-  $ touch bar
-  $ hg --config format.revlog-compression=zstd -q commit -A -m 'add bar with a lot of repeated repeated repeated text'
-
-  $ cat .hg/requires
-  dotencode
-  fncache
-  generaldelta
-  revlogv1
-  sparserevlog
-  store
-  testonly-simplestore (reposimplestore !)
-
-  $ hg debugrevlog -c | grep 0x78
-      0x78 (x)  :   2 (100.00%)
-      0x78 (x)  : 199 (100.00%)
 
 #endif
 
 checking zlib options
 =====================
 
   $ hg init zlib-level-default
   $ hg init zlib-level-1
   $ cat << EOF >> zlib-level-1/.hg/hgrc
   > [storage]
   > revlog.zlib.level=1
   > EOF
   $ hg init zlib-level-9
   $ cat << EOF >> zlib-level-9/.hg/hgrc
   > [storage]
   > revlog.zlib.level=9
   > EOF
 
 
   $ commitone() {
   >    repo=$1
   >    cp $RUNTESTDIR/bundles/issue4438-r1.hg $repo/a
   >    hg -R $repo add $repo/a
   >    hg -R $repo commit -m some-commit
   > }
 
   $ for repo in zlib-level-default zlib-level-1 zlib-level-9; do
   >     commitone $repo
   > done
 
   $ $RUNTESTDIR/f -s */.hg/store/data/*
-  default/.hg/store/data/foo.i: size=64 (pure !)
+  default/.hg/store/data/bar.i: size=64
+  default/.hg/store/data/foo.i: size=64
   zlib-level-1/.hg/store/data/a.i: size=4146
   zlib-level-9/.hg/store/data/a.i: size=4138
   zlib-level-default/.hg/store/data/a.i: size=4138
+  zstd/.hg/store/data/foo.i: size=64 (zstd !)
 
 Test error cases
 
   $ hg init zlib-level-invalid
   $ cat << EOF >> zlib-level-invalid/.hg/hgrc
   > [storage]
   > revlog.zlib.level=foobar
   > EOF
   $ commitone zlib-level-invalid
   config error: storage.revlog.zlib.level is not a valid integer ('foobar')
   config error: storage.revlog.zlib.level is not a valid integer ('foobar')
   [30]
 
   $ hg init zlib-level-out-of-range
   $ cat << EOF >> zlib-level-out-of-range/.hg/hgrc
   > [storage]
   > revlog.zlib.level=42
   > EOF
 
   $ commitone zlib-level-out-of-range
   abort: invalid value for `storage.revlog.zlib.level` config: 42
   abort: invalid value for `storage.revlog.zlib.level` config: 42
   [255]
 
+checking details of none compression
+====================================
+
+  $ hg init none-compression --config format.revlog-compression=none
+
+  $ commitone() {
+  >    repo=$1
+  >    cp $RUNTESTDIR/bundles/issue4438-r1.hg $repo/a
+  >    hg -R $repo add $repo/a
+  >    hg -R $repo commit -m some-commit
+  > }
+
+  $ commitone none-compression
+
+  $ hg log -R none-compression
+  changeset:   0:68b53da39cd8
+  tag:         tip
+  user:        test
+  date:        Thu Jan 01 00:00:00 1970 +0000
+  summary:     some-commit
+  
+
+  $ cat none-compression/.hg/requires
+  dotencode
+  exp-compression-none
+  fncache
+  generaldelta
+  revlogv1
+  sparserevlog
+  store
+  testonly-simplestore (reposimplestore !)
+
+  $ $RUNTESTDIR/f -s none-compression/.hg/store/data/*
+  none-compression/.hg/store/data/a.i: size=4216
+
 #if zstd
 
 checking zstd options
 =====================
 
   $ hg init zstd-level-default --config format.revlog-compression=zstd
   $ hg init zstd-level-1 --config format.revlog-compression=zstd
   $ cat << EOF >> zstd-level-1/.hg/hgrc
   > [storage]
   > revlog.zstd.level=1
   > EOF
   $ hg init zstd-level-22 --config format.revlog-compression=zstd
   $ cat << EOF >> zstd-level-22/.hg/hgrc
   > [storage]
   > revlog.zstd.level=22
   > EOF
 
 
   $ commitone() {
   >    repo=$1
   >    cp $RUNTESTDIR/bundles/issue4438-r1.hg $repo/a
   >    hg -R $repo add $repo/a
   >    hg -R $repo commit -m some-commit
   > }
 
   $ for repo in zstd-level-default zstd-level-1 zstd-level-22; do
   >     commitone $repo
   > done
 
   $ $RUNTESTDIR/f -s zstd-*/.hg/store/data/*
   zstd-level-1/.hg/store/data/a.i: size=4114
   zstd-level-22/.hg/store/data/a.i: size=4091
   zstd-level-default/\.hg/store/data/a\.i: size=(4094|4102) (re)
 
 Test error cases
 
   $ hg init zstd-level-invalid --config format.revlog-compression=zstd
   $ cat << EOF >> zstd-level-invalid/.hg/hgrc
   > [storage]
   > revlog.zstd.level=foobar
   > EOF
   $ commitone zstd-level-invalid
   config error: storage.revlog.zstd.level is not a valid integer ('foobar')
   config error: storage.revlog.zstd.level is not a valid integer ('foobar')
   [30]
 
   $ hg init zstd-level-out-of-range --config format.revlog-compression=zstd
   $ cat << EOF >> zstd-level-out-of-range/.hg/hgrc
   > [storage]
   > revlog.zstd.level=42
   > EOF
 
   $ commitone zstd-level-out-of-range
   abort: invalid value for `storage.revlog.zstd.level` config: 42
   abort: invalid value for `storage.revlog.zstd.level` config: 42
   [255]
 
 #endif