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phases: large rewrite on retract boundary...
phases: large rewrite on retract boundary The new code is still pure Python, so we still have room to going significantly faster. However its complexity of the complex part is `O(|[min_new_draft, tip]|)` instead of `O(|[min_draft, tip]|` which should help tremendously one repository with old draft (like mercurial-devel or mozilla-try). This is especially useful as the most common "retract boundary" operation happens when we commit/rewrite new drafts or when we push new draft to a non-publishing server. In this case, the smallest new_revs is very close to the tip and there is very few work to do. A few smaller optimisation could be done for these cases and will be introduced in later changesets. We still have iterate over large sets of roots, but this is already a great improvement for a very small amount of work. We gather information on the affected changeset as we go as we can put it to use in the next changesets. This extra data collection might slowdown the `register_new` case a bit, however for register_new, it should not really matters. The set of new nodes is either small, so the impact is negligible, or the set of new nodes is large, and the amount of work to do to had them will dominate the overhead the collecting information in `changed_revs`. As this new code compute the changes on the fly, it unlock other interesting improvement to be done in later changeset.
Matt Harbison - - Load All Authors

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bundles.txt
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/ mercurial / helptext / internals / bundles.txt
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A bundle is a container for repository data.
Bundles are used as standalone files as well as the interchange format
over the wire protocol used when two Mercurial peers communicate with
each other.
Headers
=======
Bundles produced since Mercurial 0.7 (September 2005) have a 4 byte
header identifying the major bundle type. The header always begins with
``HG`` and the follow 2 bytes indicate the bundle type/version. Some
bundle types have additional data after this 4 byte header.
The following sections describe each bundle header/type.
HG10
----
``HG10`` headers indicate a *changegroup bundle*. This is the original
bundle format, so it is sometimes referred to as *bundle1*. It has been
present since version 0.7 (released September 2005).
This header is followed by 2 bytes indicating the compression algorithm
used for data that follows. All subsequent data following this
compression identifier is compressed according to the algorithm/method
specified.
Supported algorithms include the following.
``BZ``
*bzip2* compression.
Bzip2 compressors emit a leading ``BZ`` header. Mercurial uses this
leading ``BZ`` as part of the bundle header. Therefore consumers
of bzip2 bundles need to *seed* the bzip2 decompressor with ``BZ`` or
seek the input stream back to the beginning of the algorithm component
of the bundle header so that decompressor input is valid. This behavior
is unique among supported compression algorithms.
Supported since version 0.7 (released December 2006).
``GZ``
*zlib* compression.
Supported since version 0.9.2 (released December 2006).
``UN``
*Uncompressed* or no compression. Unmodified changegroup data follows.
Supported since version 0.9.2 (released December 2006).
3rd party extensions may implement their own compression. However, no
authority reserves values for their compression algorithm identifiers.
HG2X
----
``HG2X`` headers (where ``X`` is any value) denote a *bundle2* bundle.
Bundle2 bundles are a container format for various kinds of repository
data and capabilities, beyond changegroup data (which was the only data
supported by ``HG10`` bundles.
``HG20`` is currently the only defined bundle2 version.
The ``HG20`` format is documented at :hg:`help internals.bundle2`.
Initial ``HG20`` support was added in Mercurial 3.0 (released May
2014). However, bundle2 bundles were hidden behind an experimental flag
until version 3.5 (released August 2015), when they were enabled in the
wire protocol. Various commands (including ``hg bundle``) did not
support generating bundle2 files until Mercurial 3.6 (released November
2015).
HGS1
----
*Experimental*
A ``HGS1`` header indicates a *streaming clone bundle*. This is a bundle
that contains raw revlog data from a repository store. (Typically revlog
data is exchanged in the form of changegroups.)
The purpose of *streaming clone bundles* are to *clone* repository data
very efficiently.
The ``HGS1`` header is always followed by 2 bytes indicating a
compression algorithm of the data that follows. Only ``UN``
(uncompressed data) is currently allowed.
``HGS1UN`` support was added as an experimental feature in version 3.6
(released November 2015) as part of the initial offering of the *clone
bundles* feature.