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# Chapter 35. Sequences

Sequence is an object designed to create a sequence of numbers.

Sequence can be used e.g. for numbering records or generating unique identifier for records being stored to database.

The generated numbers can be unique within the single graph run (non persistent sequence) or across multiple graph runs (persistent sequence).

- Persistent Sequences

- Non Persistent Sequences

The sequence can be created as internal (accessible from single graph) or external (shared among graphs). The conversion between internal and external sequences is possible.

- Internal: See Internal Sequences.

- External (shared): See External (Shared) Sequences.

Editing sequence in Sequence Dialog is described in Editing a Sequence.

Sequences can be accessed from CTL, see Sequence Functions.

| Warning
Remember that you should not use sequences in the `init()`, `preExecute()`, or `postExecute()` functions of CTL template and the same methods of Java interfaces.

If you plan to use sequences on Cluster, see Sequence in Cluster Environment.

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