upstream/mercurial-mirror Files · mercurial/help/internals/requirements.txt

exchangev2: fetch file revisions...

exchangev2: fetch file revisions Now that the server has an API for fetching file data, we can call into it to fetch file revisions. The implementation is relatively straightforward: we examine the manifests that we fetched and find all new file revisions referenced by them. We build up a mapping from file path to file nodes to manifest node. (The mapping to first manifest node allows us to map back to first changelog node/revision, which is used for the linkrev.) Once that map is built up, we iterate over it in a deterministic manner and fetch and store file data. The code is very similar to manifest fetching. So similar that we could probably extract the common bits into a generic function. With file data retrieval implemented, `hg clone` and `hg pull` are effectively feature complete, at least as far as the completeness of data transfer for essential repository data (changesets, manifests, files, phases, and bookmarks). We're still missing support for obsolescence markers, the hgtags fnodes cache, and the branchmap cache. But these are non-essential for the moment (and will be implemented later). This is a good point to assess the state of exchangev2 in terms of performance. I ran a local `hg clone` for the mozilla-unified repository using both version 1 and version 2 of the wire protocols and exchange methods. This is effectively comparing the performance of the wire protocol overhead and "getbundle" versus domain-specific commands. Wire protocol version 2 doesn't have compression implemented yet. So I tested version 1 with `server.compressionengines=none` to remove compression overhead from the equation. server before: user 220.420+0.000 sys 14.420+0.000 after: user 321.980+0.000 sys 18.990+0.000 client before: real 561.650 secs (user 497.670+0.000 sys 28.160+0.000) after: real 1226.260 secs (user 944.240+0.000 sys 354.150+0.000) We have substantial regressions on both client and server. This is obviously not desirable. I'm aware of some reasons: * Lack of hgtagsfnodes transfer (contributes significant CPU to client). * Lack of branch cache transfer (contributes significant CPU to client). * Little to no profiling / optimization performed on wire protocol version 2 code. * There appears to be a memory leak on the client and that is likely causing swapping on my machine. * Using multiple threads on the client may be counter-productive because Python. * We're not compressing on the server. * We're tracking file nodes on the client via manifest diffing rather than using linkrev shortcuts on the server. I'm pretty confident that most of these issues are addressable. But even if we can't get wire protocol version 2 on performance parity with "getbundle," I still think it is important to have the set of low level data-specific retrieval commands that we have implemented so far. This is because the existence of such commands allows flexibility in how clients access server data. Differential Revision: https://phab.mercurial-scm.org/D4491

Augie Fackler - - Load All Authors

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Gregory Szorc help: document requirements...	r28523	Repositories contain a file (``.hg/requires``) containing a list of
		features/capabilities that are required for clients to interface
		with the repository. This file has been present in Mercurial since
		version 0.9.2 (released December 2006).

		One of the first things clients do when opening a repository is read
		``.hg/requires`` and verify that all listed requirements are supported,
		aborting if not. Requirements are therefore a strong mechanism to
		prevent incompatible clients from reading from unknown repository
		formats or even corrupting them by writing to them.

		Extensions may add requirements. When they do this, clients not running
		an extension will be unable to read from repositories.

		The following sections describe the requirements defined by the
		Mercurial core distribution.

		revlogv1
Gregory Szorc help: don't try to render a section on sub-topics...	r29747	========
Gregory Szorc help: document requirements...	r28523
		When present, revlogs are version 1 (RevlogNG). RevlogNG was introduced
		in 2006. The ``revlogv1`` requirement has been enabled by default
		since the ``requires`` file was introduced in Mercurial 0.9.2.

		If this requirement is not present, version 0 revlogs are assumed.

		store
Gregory Szorc help: don't try to render a section on sub-topics...	r29747	=====
Gregory Szorc help: document requirements...	r28523
		The store repository layout should be used.

		This requirement has been enabled by default since the ``requires`` file
		was introduced in Mercurial 0.9.2.

		fncache
Gregory Szorc help: don't try to render a section on sub-topics...	r29747	=======
Gregory Szorc help: document requirements...	r28523
		The fncache repository layout should be used.

		The fncache layout hash encodes filenames with long paths and
		encodes reserved filenames.

		This requirement is enabled by default when the store requirement is
		enabled (which is the default behavior). It was introduced in Mercurial
		1.1 (released December 2008).

		shared
Gregory Szorc help: don't try to render a section on sub-topics...	r29747	======
Gregory Szorc help: document requirements...	r28523
		Denotes that the store for a repository is shared from another location
		(defined by the ``.hg/sharedpath`` file).

		This requirement is set when a repository is created via :hg:`share`.

		The requirement was added in Mercurial 1.3 (released July 2009).

Dan Villiom Podlaski Christiansen share: add --relative flag to store a relative path to the source...	r31133	relshared
		=========

		Derivative of ``shared``; the location of the store is relative to the
		store of this repository.

		This requirement is set when a repository is created via :hg:`share`
		using the ``--relative`` option.

		The requirement was added in Mercurial 4.2 (released May 2017).

Gregory Szorc help: document requirements...	r28523	dotencode
Gregory Szorc help: don't try to render a section on sub-topics...	r29747	=========
Gregory Szorc help: document requirements...	r28523
		The dotencode repository layout should be used.

		The dotencode layout encodes the first period or space in filenames
		to prevent issues on OS X and Windows.

		This requirement is enabled by default when the store requirement
		is enabled (which is the default behavior). It was introduced in
		Mercurial 1.7 (released November 2010).

		parentdelta
Gregory Szorc help: don't try to render a section on sub-topics...	r29747	===========
Gregory Szorc help: document requirements...	r28523
		Denotes a revlog delta encoding format that was experimental and
		replaced by generaldelta. It should not be seen in the wild because
		it was never enabled by default.

		This requirement was added in Mercurial 1.7 and removed in Mercurial
		1.9.

		generaldelta
Gregory Szorc help: don't try to render a section on sub-topics...	r29747	============
Gregory Szorc help: document requirements...	r28523
		Revlogs should be created with the generaldelta flag enabled. The
		generaldelta flag will cause deltas to be encoded against a parent
		revision instead of the previous revision in the revlog.

		Support for this requirement was added in Mercurial 1.9 (released
		July 2011). The requirement was disabled on new repositories by
		default until Mercurial 3.7 (released February 2016).

		manifestv2
Gregory Szorc help: don't try to render a section on sub-topics...	r29747	==========
Gregory Szorc help: document requirements...	r28523
		Denotes that version 2 of manifests are being used.

		Support for this requirement was added in Mercurial 3.4 (released
Augie Fackler cleanup: say goodbye to manifestv2 format...	r36391	May 2015). The new format failed to meet expectations and support
		for the format and requirement were removed in Mercurial 4.6
		(released May 2018) since the feature never graduated frome experiment
		status.
Gregory Szorc help: document requirements...	r28523
		treemanifest
Gregory Szorc help: don't try to render a section on sub-topics...	r29747	============
Gregory Szorc help: document requirements...	r28523
		Denotes that tree manifests are being used. Tree manifests are
		one manifest per directory (as opposed to a single flat manifest).

		Support for this requirement was added in Mercurial 3.4 (released
		August 2015). The requirement is currently experimental and is
		disabled by default.
Gregory Szorc sparse: add a requirement when a repository uses sparse (BC)...	r33556
		exp-sparse
		==========

		The working directory is sparse (only contains a subset of files).

		Support for this requirement was added in Mercurial 4.3 (released
		August 2017). This requirement and feature are experimental and may
		disappear in a future Mercurial release. The requirement will only
		be present on repositories that have opted in to a sparse working
		directory.

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