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Update _schema and box.once description
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‎doc/reference/reference_lua/box_once.rst‎

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.. _box-once:
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-------------------------------------------------------------------------------
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Function box.once
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-------------------------------------------------------------------------------
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Function box.once
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=================
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.. function:: box.once(key, function[, ...])
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stopping the database. The solution is to delete the ``once`` object from
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the system space :ref:`_schema <box_space-schema>`.
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Say ``box.space._schema:select{}``, find your ``once`` object there and
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delete it. For example, re-executing a block with ``key='hello'`` :
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delete it.
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When ``box.once()`` is used for initialization, it may be useful to
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wait until the database is in an appropriate state (read-only or read-write).
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In that case, see the functions in the :doc:`/reference/reference_lua/box_ctl`.
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.. code-block:: tarantoolsession
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:param string key: a value that will be checked
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:param function function: a function
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:param ...: arguments that must be passed to function
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.. NOTE::
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The parameter ``key`` will be stored in the :ref:`_schema <box_space-schema>`
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system space after ``box.once()`` is called in order to prevent a double
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run. These keys are global per replica set. So a simultaneous call of
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``box.once()`` with the same key on two instances of the same replica set
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may succeed on both of them, but it'll lead to a transaction conflict.
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**Example**
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The example shows how to re-execute the ``box.once()`` block that contains the ``hello`` key.
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First, check the ``_schema`` system space.
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The ``_schema`` space in the example contains two ``box.once`` objects -- ``oncebye`` and ``oncehello``:
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tarantool> box.space._schema:select{}
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.. code-block:: console
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app:instance001> box.space._schema:select{}
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---
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- - ['cluster', 'b4e15788-d962-4442-892e-d6c1dd5d13f2']
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- ['max_id', 512]
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- ['oncebye']
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- - ['oncebye']
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- ['oncehello']
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- ['version', 1, 7, 2]
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...
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- ['replicaset_name', 'replicaset001']
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- ['replicaset_uuid', '72d2d9bf-5d9f-48c4-ba80-9d657e128fee']
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- ['version', 3, 1, 0]
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Delete the ``oncehello`` object:
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.. code-block:: console
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tarantool> box.space._schema:delete('oncehello')
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app:instance001> box.space._schema:delete('oncehello')
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---
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- ['oncehello']
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...
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tarantool> box.once('hello', function() end)
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After that, check the ``_schema`` space again:
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.. code-block:: console
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app:instance001> box.space._schema:select{}
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---
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- - ['oncebye']
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- ['replicaset_name', 'replicaset001']
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- ['replicaset_uuid', '72d2d9bf-5d9f-48c4-ba80-9d657e128fee']
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- ['version', 3, 1, 0]
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...
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:param string key: a value that will be checked
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:param function function: a function
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:param ...: arguments that must be passed to function
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To re-execute the function, call the ``box.once()`` method again:
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.. NOTE::
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.. code-block:: console
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app:instance001> box.once('hello', function() end)
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---
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...
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app:instance001> box.space._schema:select{}
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---
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- - ['oncebye']
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- ['oncehello']
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- ['replicaset_name', 'replicaset001']
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- ['replicaset_uuid', '72d2d9bf-5d9f-48c4-ba80-9d657e128fee']
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- ['version', 3, 1, 0]
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...
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The parameter ``key`` will be stored in the :ref:`_schema <box_space-schema>`
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system space after ``box.once()`` is called in order to prevent a double
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run. These keys are global per replica set. So a simultaneous call of
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``box.once()`` with the same key on two instances of the same replica set
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may succeed on both of them, but it'll lead to a transaction conflict.

‎doc/reference/reference_lua/box_space/_schema.rst‎

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.. _box_space-schema:
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===============================================================================
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box.space._schema
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===============================================================================
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=================
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.. module:: box.space
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This space contains the following tuples:
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* ``version`` tuple with version information for this Tarantool instance,
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* ``cluster`` tuple with the instance's replica set ID,
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* ``max_id`` tuple with the maximal space ID,
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* ``once...`` tuples that correspond to specific
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:doc:`box.once() </reference/reference_lua/box_once>` blocks from the instance's
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* ``version``: version information for this Tarantool instance.
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* ``replicaset_name`` (since :doc:`3.0.0 <release/3.0.0>`): the name of a replica set to which this instance belongs.
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* ``replicaset_uuid`` (since :doc:`3.0.0 <release/3.0.0>`): the instance's replica set UUID. In version :doc:`3.0.0 <release/3.0.0>`,
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the field was renamed from ``cluster`` to ``replicaset_uuid``.
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* ``max_id`` (deprecated since :doc:`2.11.1 <https://github.com/tarantool/tarantool/releases/tag/2.11.1>`__): the maximal space ID.
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Use the :ref:`box.space._space.index[0]:max() <box_index-max>` function instead.
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* ``once...``: tuples that correspond to specific
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:ref:`box.once() <box-once>` blocks from the instance's
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:ref:`initialization file <index-init_label>`.
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The first field in these tuples contains the ``key`` value from the
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corresponding ``box.once()`` block prefixed with 'once' (e.g. `oncehello`),
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corresponding ``box.once()`` block prefixed with 'once' (for example, ``oncehello``),
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so you can easily find a tuple that corresponds to a specific
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``box.once()`` block.
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**Example:**
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Here is what ``_schema`` contains in a typical installation (notice the
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tuples for two ``box.once()`` blocks, ``'oncebye'`` and ``'oncehello'``):
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In the example, the ``_schema`` space contains two ``box.once`` objects -- ``oncebye`` and ``oncehello``.
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.. code-block:: tarantoolsession
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.. code-block:: tarantoolsession
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app:instance001> box.space._schema:select{}
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---
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- - ['oncebye']
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- ['oncehello']
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- ['replicaset_name', 'replicaset001']
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- ['replicaset_uuid', '72d2d9bf-5d9f-48c4-ba80-9d657e128fee']
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- ['version', 3, 1, 0]
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...
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tarantool> box.space._schema:select{}
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---
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- - ['cluster', 'b4e15788-d962-4442-892e-d6c1dd5d13f2']
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- ['max_id', 512]
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- ['oncebye']
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- ['oncehello']
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- ['version', 1, 7, 2]

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