================
Memory Connector
================

The Memory connector stores all data and metadata in RAM on workers
and both are discarded when Presto restarts.

.. warning::

    This connector is in early experimental stage it is not recommended
    to use it in a production environment. The intended use of this
    connector at this point is purely for testing.

.. warning::

    After ``DROP TABLE`` memory is not released immediately. It is released
    after next write access to memory connector.

.. warning::

    When one worker fails/restarts all data that were stored in it's
    memory will be lost forever. To prevent silent data loss this
    connector will throw an error on any read access to such corrupted
    table.

.. warning::

    When query fails for any reason during writing to memory table,
    table will be in undefined state. Such table should be dropped and
    recreated manually. Reading attempt from such table may fail or may
    return partial data.

.. warning::

    When coordinator fails/restarts all metadata about tables will
    be lost, but tables' data will be still present on the workers
    however they will be inaccessible.

.. warning::

    This connector will not work properly with multiple coordinators,
    since each coordinator will have a different metadata.

Configuration
-------------

To configure the Memory connector, create a catalog properties file
``~/.prestoadmin/catalog/memory.properties`` with the following contents:

.. code-block:: none

    connector.name=memory
    memory.max-data-per-node=128MB

``memory.max-data-per-node`` defines memory limit for pages stored in this
connector per each node (default value is 128MB).

Examples
--------

Create a table using the Memory connector::

    CREATE TABLE memory.default.nation AS
    SELECT * from tpch.tiny.nation;

Insert data into a table in the Memory connector::

    INSERT INTO memory.default.nation
    SELECT * FROM tpch.tiny.nation;

Select from the Memory connector::

    SELECT * FROM memory.default.nation;

Drop table::

    DROP TABLE memory.default.nation;