Jon Nelson <jnelson+pgsql@xxxxxxxxxxx> writes: > I ran a query recently where the result was very large. The outer-most > part of the query looked like this: > HashAggregate (cost=56886512.96..56886514.96 rows=200 width=30) > -> Result (cost=0.00..50842760.97 rows=2417500797 width=30) > The row count for 'Result' is in the right ballpark, but why does > HashAggregate think that it can turn 2 *billion* rows of strings (an > average of 30 bytes long) into only 200? 200 is the default assumption about number of groups when it's unable to make any statistics-based estimate. You haven't shown us any details so it's hard to say more than that. regards, tom lane -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
