To reduce recovery time, checkpoints are used for the Rollback Recovery and the Precise Recovery. More specifically, there are two actions done when a checkpoint is reached:
- Tell BaDaSt that all elements before the checkpoint can be discarded.
- Make a processing image. A processing image contains all operator states in a query processing of Odysseus at a given point in time. An operator state consists of all information an operator stores for the next element to process (e.g., sums, counts). A queue state consists of all elements that are in Odysseus waiting to be processed by an operator.
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