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Diffstat (limited to 'lib/spack/docs/environments.rst')
| -rw-r--r-- | lib/spack/docs/environments.rst | 73 |
1 files changed, 51 insertions, 22 deletions
diff --git a/lib/spack/docs/environments.rst b/lib/spack/docs/environments.rst index fca70d8af9..72882c6c71 100644 --- a/lib/spack/docs/environments.rst +++ b/lib/spack/docs/environments.rst @@ -273,19 +273,9 @@ or Concretizing ^^^^^^^^^^^^ -Once some user specs have been added to an environment, they can be -concretized. *By default specs are concretized separately*, one after -the other. This mode of operation permits to deploy a full -software stack where multiple configurations of the same package -need to be installed alongside each other. Central installations done -at HPC centers by system administrators or user support groups -are a common case that fits in this behavior. -Environments *can also be configured to concretize all -the root specs in a unified way* to ensure that -each package in the environment corresponds to a single concrete spec. This -mode of operation is usually what is required by software developers that -want to deploy their development environment. - +Once some user specs have been added to an environment, they can be concretized. +There are at the moment three different modes of operation to concretize an environment, +which are explained in details in :ref:`environments_concretization_config`. Regardless of which mode of operation has been chosen, the following command will ensure all the root specs are concretized according to the constraints that are prescribed in the configuration: @@ -493,25 +483,64 @@ Appending to this list in the yaml is identical to using the ``spack add`` command from the command line. However, there is more power available from the yaml file. +.. _environments_concretization_config: + ^^^^^^^^^^^^^^^^^^^ Spec concretization ^^^^^^^^^^^^^^^^^^^ +An environment can be concretized in three different modes and the behavior active under any environment +is determined by the ``concretizer:unify`` property. By default specs are concretized *separately*, one after the other: -Specs can be concretized separately or together, as already -explained in :ref:`environments_concretization`. The behavior active -under any environment is determined by the ``concretizer:unify`` property: +.. code-block:: yaml + + spack: + specs: + - hdf5~mpi + - hdf5+mpi + - zlib@1.2.8 + concretizer: + unify: false + +This mode of operation permits to deploy a full software stack where multiple configurations of the same package +need to be installed alongside each other using the best possible selection of transitive dependencies. The downside +is that redundancy of installations is disregarded completely, and thus environments might be more bloated than +strictly needed. In the example above, for instance, if a version of ``zlib`` newer than ``1.2.8`` is known to Spack, +then it will be used for both ``hdf5`` installations. + +If redundancy of the environment is a concern, Spack provides a way to install it *together where possible*, +i.e. trying to maximize reuse of dependencies across different specs: .. code-block:: yaml spack: specs: - - ncview - - netcdf - - nco - - py-sphinx + - hdf5~mpi + - hdf5+mpi + - zlib@1.2.8 + concretizer: + unify: when_possible + +Also in this case Spack allows having multiple configurations of the same package, but privileges the reuse of +specs over other factors. Going back to our example, this means that both ``hdf5`` installations will use +``zlib@1.2.8`` as a dependency even if newer versions of that library are available. +Central installations done at HPC centers by system administrators or user support groups are a common case +that fits either of these two modes. + +Environments can also be configured to concretize all the root specs *together*, in a self-consistent way, to +ensure that each package in the environment comes with a single configuration: + +.. code-block:: yaml + + spack: + specs: + - hdf5+mpi + - zlib@1.2.8 concretizer: unify: true +This mode of operation is usually what is required by software developers that want to deploy their development +environment and have a single view of it in the filesystem. + .. note:: The ``concretizer:unify`` config option was introduced in Spack 0.18 to @@ -521,9 +550,9 @@ under any environment is determined by the ``concretizer:unify`` property: .. admonition:: Re-concretization of user specs - When concretizing specs together the entire set of specs will be + When concretizing specs *together* or *together where possible* the entire set of specs will be re-concretized after any addition of new user specs, to ensure that - the environment remains consistent. When instead the specs are concretized + the environment remains consistent / minimal. When instead the specs are concretized separately only the new specs will be re-concretized after any addition. ^^^^^^^^^^^^^ |