Oracle Corporation
VECTORIZED HASH TABLES

Abstract:

Techniques are described herein for a vectorized hash table that uses very efficient grow and insert techniques. A single-probe hash table is grown via vectorized instructions that split each bucket, of the hash table, into a respective upper and lower bucket of the expanded hash table. Further, vacant slots are indicated using a vacant-slot-indicator value, e.g., `0`, and all vacant slots follow to the right of all occupied slots in a bucket. A vectorized compare instruction determines whether a value is already in the bucket. If not, the vectorized compare instruction is also used to determine whether the bucket has a vacant slot based on whether the bucket contains the vacant-slot-indicator value. To insert the value into the bucket, vectorized instructions are used to shift the values in the bucket to the right by one slot and to insert the new value into the left-most slot.