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docs for experimental --reuse argument to spack install

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Add docs for `--reuse`, along with a warning that it will likely be
removed and refactored.
This commit is contained in:
Todd Gamblin 2021-11-04 22:47:20 -07:00
parent 5efa76a033
commit 8e76244266
1 changed files with 28 additions and 0 deletions
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lib/spack/docs/basic_usage.rst
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@ -188,6 +188,34 @@ configuration a **spec**. In the commands above, ``mpileaks`` and
``mpileaks@3.0.4`` are both valid *specs*. We'll talk more about how
you can use them to customize an installation in :ref:`sec-specs`.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Reusing installed dependencies
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
.. warning::
The ``--reuse`` option described here is experimental, and it will
likely be replaced with a different option and configuration settings
in the next Spack release.
By default, when you run ``spack install``, Spack tries to build a new
version of the package you asked for, along with updated versions of
its dependencies. This gets you the latest versions and configurations,
but it can result in unwanted rebuilds if you update Spack frequently.
If you want Spack to try hard to reuse existing installations as dependencies,
you can add the ``--reuse`` option:
.. code-block:: console
$ spack install --reuse mpich
This will not do anything if ``mpich`` is already installed. If ``mpich``
is not installed, but dependencies like ``hwloc`` and ``libfabric`` are,
the ``mpich`` will be build with the installed versions, if possible.
You can use the :ref:`spack spec -I <cmd-spack-spec>` command to see what
will be reused and what will be built before you install.
.. _cmd-spack-uninstall:
^^^^^^^^^^^^^^^^^^^