@PublicEvolving public interface InputSelectable
IMPORTANT: This interface is a loose contract. The runtime may read multiple records
continuously before calling
nextSelection() again to determine whether to change the
input to be read. That is, it is not guaranteed that
nextSelection() will be called
immediately after the operator has processed a record and the reading input will be changed
InputSelection returned. This means that the operator may receive some data
that it does not currently want to process. Therefore, if an operator needs a strict convention,
it must cache the unexpected data itself and handle them correctly.
This interface also makes the following conventions: 1.The runtime must call
nextSelection() to determine the input to read the first record. 2.When the input being read
reaches the end, the runtime must call
nextSelection() to determine the next input to be
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