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
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.