Question

When we should not use hash joins in sql-server ? What are the various scenarios where using hash join will result in slower performance of query ?

Kindly share.

Answer 1

Hash Joins work amazingly well for larger datasets, especially if there are no indexes or table sizes vary a lot.

The two main considerations for not using hash joins on smaller datasets are:

1. Memory constraints

   • Hash joins are memory intensive and try to load at least one of the tables completely into memory. If you run out of memory, it needs to write records to disk or tempdb in a recursive fashion

2. Concurrency

   • Hash joins are not preferred for high amounts of concurrent users as it will simply eat up your resources if it needs to build a couple of in memory tables for each join requested.