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==============
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System ops
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==============
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.. module:: SysOp
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:noindex:
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System ops start with a double-colon ``::`` and must appear alone in a script.
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In the following, we explain what each system op does, and the arguments they expect.
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--------------
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Explain
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--------------
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.. function:: ::explain { <query> }
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A single query is enclosed in curly braces. Query options are allowed but ignored.
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The query is not executed, but its query plan is returned instead.
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Currently, there is no specification for the return format,
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but if you are familiar with the semi-naïve evaluation of stratified Datalog programs
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subject to magic-set rewrites, the returned data is pretty self-explanatory.
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----------------------------------
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Ops on stored relations
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----------------------------------
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.. function:: ::relations
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List all stored relations currently in the database
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.. function:: ::columns <REL_NAME>
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List all columns for the stored relation ``<REL_NAME>``.
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.. function:: ::remove <REL_NAME> (, <REL_NAME>)*
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Remove stored relations. Several can be specified, joined by commas.
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.. function:: ::rename <OLD_NAME> -> <NEW_NAME> (, <OLD_NAME> -> <NEW_NAME>)*
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Rename stored relation ``<OLD_NAME>`` into ``<NEW_NAME>``. Several may be specified, joined by commas.
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.. function:: ::show_triggers <REL_NAME>
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Display triggers associated with the stored relation ``<REL_NAME>``.
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.. function:: ::set_triggers <REL_NAME> <TRIGGERS>
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Set triggers for the stored relation ``<REL_NAME>``. This is explained in more detail in the transactions chapter.
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.. function:: ::access_level <REL_NAME> <ACCESS_LEVEL>
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Sets the access level of ``<REL_NAME>`` to the given level. The levels are:
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* ``normal`` allows everything,
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* ``protected`` disallows ``::remove`` and ``:replace``,
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* ``read_only`` additionally disallows any mutations and setting triggers,
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* ``hidden`` additionally disallows any data access (metadata access via ``::relations``, etc., are still allowed).
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It is recommended to give the appropriate access levels to tables to prevent data loss from programming mistakes.
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------------------------------------
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Monitor and kill
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------------------------------------
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.. function:: ::running
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Display currently running queries and their IDs.
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.. function:: ::kill <ID>
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Kill a running query specified by ``<ID>``. The ID may be obtained by ``::running``.
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------------------------------------
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Maintenance
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------------------------------------
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.. function:: ::compact
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Run compaction on the database. Running this may make the database smaller on disk and faster for queries,
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but running the op itself may take some time in the background.
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