April 2015
Intermediate to advanced
504 pages
11h 41m
English
A SQL statement can be slow for a lot of reasons. Here, we will give a short list of these, with at least one way of recognizing each reason.
Perform the following steps:
EXPLAIN ANALYZE to see how much data is processed in order to complete the query, as follows:mydb=# EXPLAIN ANALYZE SELECT count(*) FROM t; QUERY PLAN ------------------------------------------------------------------ Aggregate (cost=4427.27..4427.28 rows=1 width=0) \ (actual time=32.953..32.954 rows=1 loops=1) -> Seq Scan on t (cost=0.00..4425.01 rows=901 width=0) \ (actual time=30.350..31.646 rows=901 loops=1) Total runtime: 33.028 ms (3 rows)