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Since historical data is one of the most valuable items in SCADA and MES systems, the archive process is one of the first to be configured as redundant. On two (or more) computers, a pair of watchdog + D2000 Archiv process processes is configured using the SCS Config utility with the parameter /W<name>,<instance> indicating the name and number of the instance (e.g. /WSELF,1 or /WSELF,2) and with the parameter /S, /RD, or /RF specifying the server or redundancy group to which the archive connects (see Starting user processes).
Each of the instance archive processes instances archives the same historical values (children of SELF.ARC). The D2000 Server process controls which instance is active (to which read requests are directed). Other instances are passive.
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The Arcsynchro utility, which D2000 Archive Archiv can run automatically at startup (see the ArcsynchroAuto archive parameter), is used to synchronize data between archives (patching a hole after a failure of one of the instance archives or migrating archive data between different SQL databases).
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Historical value filled from a script (value storage) serves as a store of values that are not created by direct archiving of values of another object in the system, statistical calculation, or calculation in a calculated historical value. Filling in values is only possible from the ESL script or manually through the D2000 HI process. The value storage can be variable or periodic. The periodic value storage can have value playback enabled - in real time it publishes the values that were previously inserted by the script (e.g. production planning data).
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Each historical value can have its own history depth configured. The D2000 Archive process Archiv process periodically deletes values older than the history depth every few hours in such a way that at least one value older than the history depth history depth always remains.
In addition, it is possible to configure in the D2000 Archiv process the so-called depository databases that provide time-unlimited archiving for those historical values that have the Depository option enabled.
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- By opening a graph - the D2000 HI process automatically generates requests to read all the values displayed in the graph.
- By opening a picture in history mode.
- By actions for reading from the archive: GETARCHVAL, GETARCHARR, GETARCHARR_TO_CNT, GETARCHROW, GETARCHCOL, and GETARCHSTRUCT.
- By requesting historical values from outside the D2000 system:
- Reading via the D2000 Gateway from another D2000 system as a response to the GETOLDVAL command.
- Reading via D2000 Kom process (server protocols, e.g. IEC 870-5-104 Server).
- Reading via D2000 OBJApi function GetArchivData.
- Reading via D2000 VBApi (from Microsoft Visual Basic or Microsoft Excel programs) with functions VBApiGetArchData (simple historical value) or VBApiGetArchDataItem (item of a structured historical value).
- Reading via D2000 Java API.
- Reading via D2000 ODBC driver,
- Reading via D2000 REST API.
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