May 2018
Intermediate to advanced
576 pages
30h 25m
English
Force index usage and compare plan costs with an index and without, as follows:
postgres=# EXPLAIN ANALYZE SELECT count(*) FROM itable WHERE id > 500; QUERY PLAN--------------------------------------------------------------------- Aggregate (cost=188.75..188.76 rows=1 width=0) (actual time=37.958..37.959 rows=1 loops=1) -> Seq Scan on itable (cost=0.00..165.00 rows=9500 width=0) (actual time=0.290..18.792 rows=9500 loops=1) Filter: (id > 500) Total runtime: 38.027 ms(4 rows)postgres=# SET enable_seqscan TO false;SETpostgres=# EXPLAIN ANALYZE SELECT count(*) FROM itable WHERE id > 500; QUERY PLAN--------------------------------------------------------------------- Aggregate (cost=323.25..323.26 rows=1 width=0) (actual time=44.467..44.469 ...