annotate mercurial/help/pager.txt @ 42237:9f45d3d526f9

hgtagsfnodescache: inherit fnode from parent when possible

If a changeset does not update the content of `.hgtags`, it means it will use
the same file-node (for `.hgtags`) as its parents. In this case we can
directly reuse the parent's file-node.

We use this property when updating the `hgtagsfnodescache` taking a faster path
if we already have a cached value for the parents of the node we are looking
at.

Doing so provides a large performance boost when looking at a lot of fnodes,
especially on repository with very large manifest:

timing for `tagsmod.fnoderevs(ui, repo, repo.changelog.revs())`

mercurial: (41907 revisions, 1923 files)

    before: 6.9 seconds
    after:  2.7 seconds (-54%)

pypy: (96266 revisions, 5198 files)

    before: 80 seconds
    after:  20 seconds (-75%)

mozilla-central: (463411 revisions, 272080 files)

    before: 7166.4 seconds
    after:    47.8 seconds (-99%, x150 speedup)

On a copy of mozilla-try with about 35K heads ans 1.7M changesets, this moves
the computation from many hours to a couple of minutes, making it more
interesting to do a full warm up of this cache before computing tags (from a
cold cache).

There seems to be other performance low hanging fruits, like avoiding the use of
changectx or a more revision centric logic. However, the new code is fast enough
for my needs right now.

Some Mercurial commands can produce a lot of output, and Mercurial will
attempt to use a pager to make those commands more pleasant.

To set the pager that should be used, set the application variable::

  [pager]
  pager = less -FRX

If no pager is set in the user or repository configuration, Mercurial uses the
environment variable $PAGER. If $PAGER is not set, pager.pager from the default
or system configuration is used. If none of these are set, a default pager will
be used, typically `less` on Unix and `more` on Windows.

.. container:: windows

  On Windows, `more` is not color aware, so using it effectively disables color.
  MSYS and Cygwin shells provide `less` as a pager, which can be configured to
  support ANSI color codes.  See :hg:`help config.color.pagermode` to configure
  the color mode when invoking a pager.

You can disable the pager for certain commands by adding them to the
pager.ignore list::

  [pager]
  ignore = version, help, update

To ignore global commands like :hg:`version` or :hg:`help`, you have
to specify them in your user configuration file.

To control whether the pager is used at all for an individual command,
you can use --pager=<value>:

  - use as needed: `auto`.
  - require the pager: `yes` or `on`.
  - suppress the pager: `no` or `off` (any unrecognized value
    will also work).

To globally turn off all attempts to use a pager, set::

  [ui]
  paginate = never

which will prevent the pager from running.