mercurial/help/urls.txt

sparse-read: move from a recursive-based approach to a heap-based one

The previous recursive approach was trying to optimise each read slice to have
a good density. It had the tendency to over-optimize smaller slices while
leaving larger hole in others.

The new approach focuses on improving the combined density of all the reads,
instead of the individual slices. It slices at the largest gaps first, as they
reduce the total amount of read data the most efficiently.

Another benefit of this approach is that we iterate over the delta chain only
once, reducing the overhead of slicing long delta chains.

On the repository we use for tests, the new approach shows similar or faster
performance than the current default linear full read.

The repository contains about 450,000 revisions with many concurrent
topological branches. Tests have been run on two versions of the repository:
one built with the current delta constraint, and the other with an unlimited
delta span (using 'experimental.maxdeltachainspan=0')

Below are timings for building 1% of all the revision in the manifest log using
'hg perfrevlogrevisions -m'. Times are given in seconds. They include the new
couple of follow-up changeset in this series.

delta-span  standard    unlimited
linear-read     922s         632s
sparse-read     814s         566s

Valid URLs are of the form::

  local/filesystem/path[#revision]
  file://local/filesystem/path[#revision]
  http://[user[:pass]@]host[:port]/[path][#revision]
  https://[user[:pass]@]host[:port]/[path][#revision]
  ssh://[user@]host[:port]/[path][#revision]

Paths in the local filesystem can either point to Mercurial
repositories or to bundle files (as created by :hg:`bundle` or
:hg:`incoming --bundle`). See also :hg:`help paths`.

An optional identifier after # indicates a particular branch, tag, or
changeset to use from the remote repository. See also :hg:`help
revisions`.

Some features, such as pushing to http:// and https:// URLs are only
possible if the feature is explicitly enabled on the remote Mercurial
server.

Note that the security of HTTPS URLs depends on proper configuration of
web.cacerts.

Some notes about using SSH with Mercurial:

- SSH requires an accessible shell account on the destination machine
  and a copy of hg in the remote path or specified with as remotecmd.
- path is relative to the remote user's home directory by default. Use
  an extra slash at the start of a path to specify an absolute path::

    ssh://example.com//tmp/repository

- Mercurial doesn't use its own compression via SSH; the right thing
  to do is to configure it in your ~/.ssh/config, e.g.::

    Host *.mylocalnetwork.example.com
      Compression no
    Host *
      Compression yes

  Alternatively specify "ssh -C" as your ssh command in your
  configuration file or with the --ssh command line option.

These URLs can all be stored in your configuration file with path
aliases under the [paths] section like so::

  [paths]
  alias1 = URL1
  alias2 = URL2
  ...

You can then use the alias for any command that uses a URL (for
example :hg:`pull alias1` will be treated as :hg:`pull URL1`).

Two path aliases are special because they are used as defaults when
you do not provide the URL to a command:

default:
  When you create a repository with hg clone, the clone command saves
  the location of the source repository as the new repository's
  'default' path. This is then used when you omit path from push- and
  pull-like commands (including incoming and outgoing).

default-push:
  The push command will look for a path named 'default-push', and
  prefer it over 'default' if both are defined.