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HSJOIN

Short Description

The HSJOIN operator indicates the use of a hash join

Detailed Description​

The HSJOIN operator indicates the use of a hash join. Filtered rows from the table are hashed. A hash join is efficient because the join can be performed without pre-sorting the join data. Hash joins can also be seen when subqueries are rewritten as can be the case with the NLJOIN.

The hash table is created from the inner table rows and then values are hashed from the outer table to see if there is a match.

Performance can be optimized by restricting predicates to just one table and restricting the number of rows selected, ensuring the sort heap size is large enough to hold the has table in memory and making sure statistics are up to date by running RUNSTATS.

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