.. _conf.seq.sched.replay:

===================
Replay Instructions
===================

Replay instructions allow you to rerun scheduling tasks from a specific point in time - effectively “rewinding the clock” to reprocess historical data.

You can configure a replay by selecting a replay instruction when setting up either a single instruction or an instruction sequence.

The following are available replay instructions:


.. list-table:: 
   :widths: 1 1 5
   :header-rows: 1
   :class: tight-table

   * - Service
     - Instruction
     - Description
   * - **AlarmEventService**
     - ``ScanAlarmByRange`` (Event Replay - Run Once)
     - Scans a specific Alarm/Event over a defined date range. *(Available for Single Instruction or Non-Recurring Instruction Sequence)*
   * - **AlarmEventService**
     - ``ScanEventGroupByRange`` (Event Group Replay - Run Once)
     - Scans a specific Event Group over a defined date range. *(Available for Single Instruction or Non-Recurring Instruction Sequence)*
   * - **CalcEngineService**
     - ``Calculation Group Replay``
     - Scans a specific Calculation Group over a defined date range. *(Available for Single Instruction or Non-Recurring Instruction Sequence)*
   * - **DataService**
     - ``ScanAggregateGroupByRange`` (Aggregate Group Replay)
     - Scans a specific Aggregate Group over a defined date range. *(Available for Single Instruction or Non-Recurring Instruction Sequence)*
   * - **DataService**
     - ``Simple Historize Group by Range``
     - Performs simple historization of the last value of all input tags into output tags at a specified frequency. If frequency is not set or is 0, a default of 1 minute is used.
   * - **ExternalDataService**
     - ``InstructDataConnectorReadHistorical``
     - Instructs a data connector to read historical values
   * - **ExternalDataService**
     - ``InstructDataConnectorWriteHistorical``
     - Instructs a data connector to write historical values




When configuring a replay instruction, you must define a time range using one of the following options:

- **Absolute** - Specify both a start and end time.
- **Relative** - The start time is optional. If omitted, the system time at execution will be used.  
  You can also use a negative value in **Seconds From Start Time** to go backwards in time.

.. note::

   When choosing the **Absolute** option, the value in the **End Time** field is ignored for the ``AlarmEventService``, ``CalcEngineService`` and ``DataService-AggregateGroup`` instructions.  
   Replays always process data up to the current system time, regardless of the end time specified.