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class AggregateHashMap extends AnyRef

This is an illustrative implementation of an append-only single-key/single value aggregate hash map that can act as a 'cache' for extremely fast key-value lookups while evaluating aggregates (and fall back to the BytesToBytesMap if a given key isn't found). This can be potentially 'codegened' in HashAggregate to speed up aggregates w/ key.

It is backed by a power-of-2-sized array for index lookups and a columnar batch that stores the key-value pairs. The index lookups in the array rely on linear probing (with a small number of maximum tries) and use an inexpensive hash function which makes it really efficient for a majority of lookups. However, using linear probing and an inexpensive hash function also makes it less robust as compared to the BytesToBytesMap (especially for a large number of keys or even for certain distribution of keys) and requires us to fall back on the latter for correctness.

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Instance Constructors

  1. new AggregateHashMap(schema: StructType)
  2. new AggregateHashMap(schema: StructType, capacity: Int, loadFactor: Double, maxSteps: Int)

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  9. def find(key: Long): Int
  10. def findOrInsert(key: Long): MutableColumnarRow
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