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The query functionality in particular is powerful and allows for very complex queries.
See Retrieving Persistent State Metadata with the PersistentStateControl Adapter for more details.

Improved Adapters

Persistent State Adapter: Performance Improvements With External Persistent State Attributes

You can mark attributes of a persistent state class as external by applying stereotype <<External>>. This can speed-up persistent state performance if you have huge data objects (like e.g. big blobs, IDocs or PDFs) that are only used in few transitions.

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