.. _Crate-Historian:

===============
Crate Historian
===============

Crate is an open source SQL database designed on top of a No-SQL design.  It allows automatic data replication and
self-healing clusters for high availability, automatic sharding, and fast joins, aggregations and sub-selects.

.. note::
   The Crate Historian is located within the **core** directory. ::

      services/core/CrateHistorian/

Find out more about crate from `<https://crate.io/>`_.


Prerequisites
=============

1. Crate Database
-----------------

For Arch Linux, Debian, RedHat Enterprise Linux and Ubuntu distributions there is a simple installer to get Crate up and
running on your system.

.. code-block:: bash

    sudo bash -c "$(curl -L https://try.crate.io)"

This command will download and install all of the requirements for running Crate, create a Crate user and install a
Crate service.  After the installation the service will be available for viewing at ``http://localhost:4200`` by
default.

.. note::

    There is no authentication support within crate.


2. Crate Driver
---------------

There is a Python library for crate that must be installed in the VOLTTRON Python virtual environment in order to access
Crate.  From an activated environment, in the root of the volttron folder, execute the following command:

.. code-block:: bash

    python bootstrap.py --crate

or

.. code-block:: bash

    python bootstrap.py --databases


or

.. code-block:: bash

    pip install crate


Configuration
=============

Because there is no authorization to access a crate database the configuration for the Crate Historian is very easy.

.. code-block:: python

    {
        "connection": {
            "type": "crate",
            # Optional table prefix defaults to historian
            "schema": "testing",
            "params": {
                "host": "localhost:4200"
            }
        }
    }

Finally package, install and start the Crate Historian agent.

.. seealso::  :ref:`Agent Development Walk-through <Agent-Packaging-and-Install>`