comparison hgext/clonebundles.py @ 37498:aacfca6f9767

wireproto: support for pullbundles

Pullbundles are similar to clonebundles, but served as normal inline
bundle streams. They are almost transparent to the client -- the only
visible effect is that the client might get less changes than what it
asked for, i.e. not all requested head revisions are provided.

The client announces support for the necessary retries with the
partial-pull capability. After receiving a partial bundle, it updates
the set of revisions shared with the server and drops all now-known
heads from the request list. It will then rerun getbundle until
no changes are received or all remote heads are present.

Extend badserverext to support per-socket limit, i.e. don't assume that
the same limits should be applied to all sockets.

Differential Revision: https://phab.mercurial-scm.org/D1856

37497:1541e1a8e87d

"""advertise pre-generated bundles to seed clones

"clonebundles" is a server-side extension used to advertise the existence
of pre-generated, externally hosted bundle files to clients that are
cloning so that cloning can be faster, more reliable, and require less
resources on the server.

Cloning can be a CPU and I/O intensive operation on servers. Traditionally,
the server, in response to a client's request to clone, dynamically generates
a bundle containing the entire repository content and sends it to the client.
There is no caching on the server and the server will have to redundantly
generate the same outgoing bundle in response to each clone request. For
servers with large repositories or with high clone volume, the load from
clones can make scaling the server challenging and costly.

This extension provides server operators the ability to offload potentially
expensive clone load to an external service. Here's how it works.

1. A server operator establishes a mechanism for making bundle files available
   on a hosting service where Mercurial clients can fetch them.
2. A manifest file listing available bundle URLs and some optional metadata
   is added to the Mercurial repository on the server.

6. The client downloads and applies an available bundle from the
   server-specified URL.
7. The client reconnects to the original server and performs the equivalent
   of :hg:`pull` to retrieve all repository data not in the bundle. (The
   repository could have been updated between when the bundle was created
   and when the client started the clone.)

Instead of the server generating full repository bundles for every clone
request, it generates full bundles once and they are subsequently reused to
bootstrap new clones. The server may still transfer data at clone time.
However, this is only data that has been added/changed since the bundle was
created. For large, established repositories, this can reduce server load for
clones to less than 1% of original.

To work, this extension requires the following of server operators:

* Generating bundle files of repository content (typically periodically,
  such as once per day).
* A file server that clients have network access to and that Python knows
  how to talk to through its normal URL handling facility (typically an
  HTTP server).
* A process for keeping the bundles manifest in sync with available bundle
  files.

Strictly speaking, using a static file hosting server isn't required: a server
operator could use a dynamic service for retrieving bundle data. However,

Bundle files can be generated with the :hg:`bundle` command. Typically
:hg:`bundle --all` is used to produce a bundle of the entire repository.

:hg:`debugcreatestreamclonebundle` can be used to produce a special
*streaming clone bundle*. These are bundle files that are extremely efficient
to produce and consume (read: fast). However, they are larger than
traditional bundle formats and require that clients support the exact set
of repository data store formats in use by the repository that created them.
Typically, a newer server can serve data that is compatible with older clients.
However, *streaming clone bundles* don't have this guarantee. **Server

streaming clone bundles incompatible with older Mercurial versions.**

A server operator is responsible for creating a ``.hg/clonebundles.manifest``
file containing the list of available bundle files suitable for seeding
clones. If this file does not exist, the repository will not advertise the
existence of clone bundles when clients connect.

The manifest file contains a newline (\\n) delimited list of entries.

Each line in this file defines an available bundle. Lines have the format:

    <URL> [<key>=<value>[ <key>=<value>]]

That is, a URL followed by an optional, space-delimited list of key=value
pairs describing additional properties of this bundle. Both keys and values
are URI encoded.

Keys in UPPERCASE are reserved for use by Mercurial and are defined below.
All non-uppercase keys can be used by site installations. An example use
for custom properties is to use the *datacenter* attribute to define which
data center a file is hosted in. Clients could then prefer a server in the

   If this is defined, it is important to advertise a non-SNI fallback
   URL or clients running old Python releases may not be able to clone
   with the clonebundles facility.

   Value should be "true".

Manifests can contain multiple entries. Assuming metadata is defined, clients
will filter entries from the manifest that they don't support. The remaining
entries are optionally sorted by client preferences
(``ui.clonebundleprefers`` config option). The client then attempts

37498:aacfca6f9767

"""advertise pre-generated bundles to seed clones

"clonebundles" is a server-side extension used to advertise the existence
of pre-generated, externally hosted bundle files to clients that are
cloning so that cloning can be faster, more reliable, and require less
resources on the server. "pullbundles" is a related feature for sending
pre-generated bundle files to clients as part of pull operations.

Cloning can be a CPU and I/O intensive operation on servers. Traditionally,
the server, in response to a client's request to clone, dynamically generates
a bundle containing the entire repository content and sends it to the client.
There is no caching on the server and the server will have to redundantly
generate the same outgoing bundle in response to each clone request. For
servers with large repositories or with high clone volume, the load from
clones can make scaling the server challenging and costly.

This extension provides server operators the ability to offload
potentially expensive clone load to an external service. Pre-generated
bundles also allow using more CPU intensive compression, reducing the
effective bandwidth requirements.

Here's how clone bundles work:

1. A server operator establishes a mechanism for making bundle files available
   on a hosting service where Mercurial clients can fetch them.
2. A manifest file listing available bundle URLs and some optional metadata
   is added to the Mercurial repository on the server.

6. The client downloads and applies an available bundle from the
   server-specified URL.
7. The client reconnects to the original server and performs the equivalent
   of :hg:`pull` to retrieve all repository data not in the bundle. (The
   repository could have been updated between when the bundle was created
   and when the client started the clone.) This may use "pullbundles".

Instead of the server generating full repository bundles for every clone
request, it generates full bundles once and they are subsequently reused to
bootstrap new clones. The server may still transfer data at clone time.
However, this is only data that has been added/changed since the bundle was
created. For large, established repositories, this can reduce server load for
clones to less than 1% of original.

Here's how pullbundles work:

1. A manifest file listing available bundles and describing the revisions
   is added to the Mercurial repository on the server.
2. A new-enough client informs the server that it supports partial pulls
   and initiates a pull.
3. If the server has pull bundles enabled and sees the client advertising
   partial pulls, it checks for a matching pull bundle in the manifest.
   A bundle matches if the format is supported by the client, the client
   has the required revisions already and needs something from the bundle.
4. If there is at least one matching bundle, the server sends it to the client.
5. The client applies the bundle and notices that the server reply was
   incomplete. It initiates another pull.

To work, this extension requires the following of server operators:

* Generating bundle files of repository content (typically periodically,
  such as once per day).
* Clone bundles: A file server that clients have network access to and that
  Python knows how to talk to through its normal URL handling facility
  (typically an HTTP/HTTPS server).
* A process for keeping the bundles manifest in sync with available bundle
  files.

Strictly speaking, using a static file hosting server isn't required: a server
operator could use a dynamic service for retrieving bundle data. However,

Bundle files can be generated with the :hg:`bundle` command. Typically
:hg:`bundle --all` is used to produce a bundle of the entire repository.

:hg:`debugcreatestreamclonebundle` can be used to produce a special
*streaming clonebundle*. These are bundle files that are extremely efficient
to produce and consume (read: fast). However, they are larger than
traditional bundle formats and require that clients support the exact set
of repository data store formats in use by the repository that created them.
Typically, a newer server can serve data that is compatible with older clients.
However, *streaming clone bundles* don't have this guarantee. **Server

streaming clone bundles incompatible with older Mercurial versions.**

A server operator is responsible for creating a ``.hg/clonebundles.manifest``
file containing the list of available bundle files suitable for seeding
clones. If this file does not exist, the repository will not advertise the
existence of clone bundles when clients connect. For pull bundles,
``.hg/pullbundles.manifest`` is used.

The manifest file contains a newline (\\n) delimited list of entries.

Each line in this file defines an available bundle. Lines have the format:

    <URL> [<key>=<value>[ <key>=<value>]]

That is, a URL followed by an optional, space-delimited list of key=value
pairs describing additional properties of this bundle. Both keys and values
are URI encoded.

For pull bundles, the URL is a path under the ``.hg`` directory of the
repository.

Keys in UPPERCASE are reserved for use by Mercurial and are defined below.
All non-uppercase keys can be used by site installations. An example use
for custom properties is to use the *datacenter* attribute to define which
data center a file is hosted in. Clients could then prefer a server in the

   If this is defined, it is important to advertise a non-SNI fallback
   URL or clients running old Python releases may not be able to clone
   with the clonebundles facility.

   Value should be "true".

heads
   Used for pull bundles. This contains the ``;`` separated changeset
   hashes of the heads of the bundle content.

bases
   Used for pull bundles. This contains the ``;`` separated changeset
   hashes of the roots of the bundle content. This can be skipped if
   the bundle was created without ``--base``.

Manifests can contain multiple entries. Assuming metadata is defined, clients
will filter entries from the manifest that they don't support. The remaining
entries are optionally sorted by client preferences
(``ui.clonebundleprefers`` config option). The client then attempts