##// END OF EJS Templates
localrepo: experimental support for non-zlib revlog compression...
localrepo: experimental support for non-zlib revlog compression The final part of integrating the compression manager APIs into revlog storage is the plumbing for repositories to advertise they are using non-zlib storage and for revlogs to instantiate a non-zlib compression engine. The main intent of the compression manager work was to zstd all of the things. Adding zstd to revlogs has proved to be more involved than other places because revlogs are... special. Very small inputs and the use of delta chains (which are themselves a form of compression) are a completely different use case from streaming compression, which bundles and the wire protocol employ. I've conducted numerous experiments with zstd in revlogs and have yet to formalize compression settings and a storage architecture that I'm confident I won't regret later. In other words, I'm not yet ready to commit to a new mechanism for using zstd - or any other compression format - in revlogs. That being said, having some support for zstd (and other compression formats) in revlogs in core is beneficial. It can allow others to conduct experiments. This patch introduces *highly experimental* support for non-zlib compression formats in revlogs. Introduced is a config option to control which compression engine to use. Also introduced is a namespace of "exp-compression-*" requirements to denote support for non-zlib compression in revlogs. I've prefixed the namespace with "exp-" (short for "experimental") because I'm not confident of the requirements "schema" and in no way want to give the illusion of supporting these requirements in the future. I fully intend to drop support for these requirements once we figure out what we're doing with zstd in revlogs. A good portion of the patch is teaching the requirements system about registered compression engines and passing the requested compression engine as an opener option so revlogs can instantiate the proper compression engine for new operations. That's a verbose way of saying "we can now use zstd in revlogs!" On an `hg pull` conversion of the mozilla-unified repo with no extra redelta settings (like aggressivemergedeltas), we can see the impact of zstd vs zlib in revlogs: $ hg perfrevlogchunks -c ! chunk ! wall 2.032052 comb 2.040000 user 1.990000 sys 0.050000 (best of 5) ! wall 1.866360 comb 1.860000 user 1.820000 sys 0.040000 (best of 6) ! chunk batch ! wall 1.877261 comb 1.870000 user 1.860000 sys 0.010000 (best of 6) ! wall 1.705410 comb 1.710000 user 1.690000 sys 0.020000 (best of 6) $ hg perfrevlogchunks -m ! chunk ! wall 2.721427 comb 2.720000 user 2.640000 sys 0.080000 (best of 4) ! wall 2.035076 comb 2.030000 user 1.950000 sys 0.080000 (best of 5) ! chunk batch ! wall 2.614561 comb 2.620000 user 2.580000 sys 0.040000 (best of 4) ! wall 1.910252 comb 1.910000 user 1.880000 sys 0.030000 (best of 6) $ hg perfrevlog -c -d 1 ! wall 4.812885 comb 4.820000 user 4.800000 sys 0.020000 (best of 3) ! wall 4.699621 comb 4.710000 user 4.700000 sys 0.010000 (best of 3) $ hg perfrevlog -m -d 1000 ! wall 34.252800 comb 34.250000 user 33.730000 sys 0.520000 (best of 3) ! wall 24.094999 comb 24.090000 user 23.320000 sys 0.770000 (best of 3) Only modest wins for the changelog. But manifest reading is significantly faster. What's going on? One reason might be data volume. zstd decompresses faster. So given more bytes, it will put more distance between it and zlib. Another reason is size. In the current design, zstd revlogs are *larger*: debugcreatestreamclonebundle (size in bytes) zlib: 1,638,852,492 zstd: 1,680,601,332 I haven't investigated this fully, but I reckon a significant cause of larger revlogs is that the zstd frame/header has more bytes than zlib's. For very small inputs or data that doesn't compress well, we'll tend to store more uncompressed chunks than with zlib (because the compressed size isn't smaller than original). This will make revlog reading faster because it is doing less decompression. Moving on to bundle performance: $ hg bundle -a -t none-v2 (total CPU time) zlib: 102.79s zstd: 97.75s So, marginal CPU decrease for reading all chunks in all revlogs (this is somewhat disappointing). $ hg bundle -a -t <engine>-v2 (total CPU time) zlib: 191.59s zstd: 115.36s This last test effectively measures the difference between zlib->zlib and zstd->zstd for revlogs to bundle. This is a rough approximation of what a server does during `hg clone`. There are some promising results for zstd. But not enough for me to feel comfortable advertising it to users. We'll get there...

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hgweb.txt
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Mercurial's internal web server, hgweb, can serve either a single
repository, or a tree of repositories. In the second case, repository
paths and global options can be defined using a dedicated
configuration file common to :hg:`serve`, ``hgweb.wsgi``,
``hgweb.cgi`` and ``hgweb.fcgi``.
This file uses the same syntax as other Mercurial configuration files
but recognizes only the following sections:
- web
- paths
- collections
The ``web`` options are thoroughly described in :hg:`help config`.
The ``paths`` section maps URL paths to paths of repositories in the
filesystem. hgweb will not expose the filesystem directly - only
Mercurial repositories can be published and only according to the
configuration.
The left hand side is the path in the URL. Note that hgweb reserves
subpaths like ``rev`` or ``file``, try using different names for
nested repositories to avoid confusing effects.
The right hand side is the path in the filesystem. If the specified
path ends with ``*`` or ``**`` the filesystem will be searched
recursively for repositories below that point.
With ``*`` it will not recurse into the repositories it finds (except for
``.hg/patches``).
With ``**`` it will also search inside repository working directories
and possibly find subrepositories.
In this example::
[paths]
/projects/a = /srv/tmprepos/a
/projects/b = c:/repos/b
/ = /srv/repos/*
/user/bob = /home/bob/repos/**
- The first two entries make two repositories in different directories
appear under the same directory in the web interface
- The third entry will publish every Mercurial repository found in
``/srv/repos/``, for instance the repository ``/srv/repos/quux/``
will appear as ``http://server/quux/``
- The fourth entry will publish both ``http://server/user/bob/quux/``
and ``http://server/user/bob/quux/testsubrepo/``
The ``collections`` section is deprecated and has been superseded by
``paths``.
URLs and Common Arguments
=========================
URLs under each repository have the form ``/{command}[/{arguments}]``
where ``{command}`` represents the name of a command or handler and
``{arguments}`` represents any number of additional URL parameters
to that command.
The web server has a default style associated with it. Styles map to
a collection of named templates. Each template is used to render a
specific piece of data, such as a changeset or diff.
The style for the current request can be overwritten two ways. First,
if ``{command}`` contains a hyphen (``-``), the text before the hyphen
defines the style. For example, ``/atom-log`` will render the ``log``
command handler with the ``atom`` style. The second way to set the
style is with the ``style`` query string argument. For example,
``/log?style=atom``. The hyphenated URL parameter is preferred.
Not all templates are available for all styles. Attempting to use
a style that doesn't have all templates defined may result in an error
rendering the page.
Many commands take a ``{revision}`` URL parameter. This defines the
changeset to operate on. This is commonly specified as the short,
12 digit hexadecimal abbreviation for the full 40 character unique
revision identifier. However, any value described by
:hg:`help revisions` typically works.
Commands and URLs
=================
The following web commands and their URLs are available:
.. webcommandsmarker