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Class ResultVectorCacheImpl

These rules create interesting constraints for the scan operator. Conceptually, each batch is distinct. But, it must share vectors. The ResultSetLoader class handles this by managing the set of vectors used by a single reader.

Readers are independent: each may read a distinct schema (as in JSON.) Yet, the Drill protocol requires minimizing spurious OK_NEW_SCHEMA events. As a result, two readers run by the same scan operator must share the same set of vectors, despite the fact that they may have different schemas and thus different ResultSetLoaders.

The purpose of this inventory is to persist vectors across readers, even when, say, reader B does not use a vector that reader A created.

The semantics supported by this class include:

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