==============
System ops
==============

.. module:: SysOp
    :noindex:

System ops start with a double-colon ``::`` and must appear alone in a script. 
In the following we explain what each system op does, and the arguments they expect.

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Explain
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.. function:: ::explain { <query> }

    A single query is enclosed in curly braces. Query options are allowed but ignored. 
    The query is not executed, but its query plan is returned instead. 
    Currently there is no specification for the return format, 
    but if you are familiar with semi-naive evaluation of stratified Datalog programs
    subject to magic-set rewrites, the returned data is pretty self-explanatory.

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Ops on stored relations
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.. function:: ::relations

    List all stored relations currently in the database

.. function:: ::relation columns <REL_NAME>

    List all columns for the stored relation ``<REL_NAME>``.

.. function:: ::relation remove <REL_NAME> (, <REL_NAME>)*

    Remove stored relations. Several can be specified, joined by commas.

.. function:: ::relation rename <OLD_NAME> -> <NEW_NAME> (, <OLD_NAME> -> <NEW_NAME>)*

    Rename stored relation ``<OLD_NAME>`` into ``<NEW_NAME>``. Several may be specified, joined by commas.

.. function:: ::relation show_triggers <REL_NAME>

    Display triggers associated with the stored relation ``<REL_NAME>``.

.. function:: ::relation set_triggers <REL_NAME> <TRIGGERS>

    Set triggers for the stored relation ``<REL_NAME>``. This is explained in more details in the transactions chapter.

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Monitor and kill
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.. function:: ::running

    Display currently running queries and their IDs.

.. function:: ::kill <ID>

    Kill a running query specified by ``<ID>``. The ID may be obtained by ``::running``.

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Maintenance
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.. function:: ::compact

    Run compaction on the database. Running this may make the database smaller on disk and faster for queries, 
    but running the op itself may take some time in the background.