sql - Amazon Redshift doing Hash Join even when joined on column that is both Dist Key and Sort Key -


i have fact table in redshift having 1.3 billion rows distribution key c1 , sort key c1, c2.

i need join table join clause on c1 (i.e. c1 1st instance of table = c1 2nd instance of table).

as see query plan of query, redshift appears doing hash join ds_dist_none. though ds_dist_none expected have both dist key , sort key on column c1, expected redshift merge join instead of hash join (again because of same reason).

i believe slowing down query.

can please explain why redshift may doing hash join instead of merge join (even though have both dist key , sort key on joining column) , redshift doing ds_dist_none query?

it turned out since not inserting data in our table in sorted order (as defined sort key of table) , redshift not automatically keep table's rows sorted sort key, there no way redshift perform merge join on our table. after running full vacuum on table, redshift started performing merge join


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