Multiple worker thread will work together to do sequential scans, joins and aggregation. Some mentions here:
<a href="http:&#x2F;&#x2F;rhaas.blogspot.com&#x2F;2016&#x2F;03&#x2F;parallel-query-is-getting-better-and.html" rel="nofollow">http:&#x2F;&#x2F;rhaas.blogspot.com&#x2F;2016&#x2F;03&#x2F;parallel-query-is-getting-...</a><p>But this is just a start and there are lots more opportunities to improve as mentioned here:
<a href="https:&#x2F;&#x2F;wiki.postgresql.org&#x2F;wiki&#x2F;Parallel_Query_Execution" rel="nofollow">https:&#x2F;&#x2F;wiki.postgresql.org&#x2F;wiki&#x2F;Parallel_Query_Execution</a>