Mercurial > hg
comparison mercurial/bundle2.py @ 35787:a84dbc87dae9
exchange: send bundle2 stream clones uncompressed
Stream clones don't compress well. And compression undermines
a point of stream clones which is to trade significant CPU
reductions by increasing size.
Building upon our introduction of metadata to communicate bundle
information back to callers of exchange.getbundlechunks(), we add
an attribute to the bundler that communicates whether the bundle is
best left uncompressed. We return this attribute as part of the bundle
metadata. And the wire protocol honors it when determining whether
to compress the wire protocol response.
The added test demonstrates that the raw result from the wire
protocol is not compressed. It also demonstrates that the server
will serve stream responses when the feature isn't enabled. We'll
address that in another commit.
The effect of this change is that server-side CPU usage for bundle2
stream clones is significantly reduced by removing zstd compression.
For the mozilla-unified repository:
before: 37.69 user 8.01 system
after: 27.38 user 7.34 system
Assuming things are CPU bound, that ~10s reduction would translate to
faster clones on the client. zstd can decompress at >1 GB/s. So the
overhead from decompression on the client is small in the grand scheme
of things. But if zlib compression were being used, the overhead would
be much greater.
Differential Revision: https://phab.mercurial-scm.org/D1926
author | Gregory Szorc <gregory.szorc@gmail.com> |
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date | Mon, 22 Jan 2018 12:12:29 -0800 |
parents | c97639ad6874 |
children | b116a66bcc44 |
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35786:8144f1b07e21 | 35787:a84dbc87dae9 |
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597 self._params = [] | 597 self._params = [] |
598 self._parts = [] | 598 self._parts = [] |
599 self.capabilities = dict(capabilities) | 599 self.capabilities = dict(capabilities) |
600 self._compengine = util.compengines.forbundletype('UN') | 600 self._compengine = util.compengines.forbundletype('UN') |
601 self._compopts = None | 601 self._compopts = None |
602 # If compression is being handled by a consumer of the raw | |
603 # data (e.g. the wire protocol), unsetting this flag tells | |
604 # consumers that the bundle is best left uncompressed. | |
605 self.prefercompressed = True | |
602 | 606 |
603 def setcompression(self, alg, compopts=None): | 607 def setcompression(self, alg, compopts=None): |
604 """setup core part compression to <alg>""" | 608 """setup core part compression to <alg>""" |
605 if alg in (None, 'UN'): | 609 if alg in (None, 'UN'): |
606 return | 610 return |