From: Venkata Balaji N [mailto:nag1010@xxxxxxxxx]
On Wed, Mar 25, 2015 at 7:00 PM, Khangelani Gama <kgama@xxxxxxxxxxxx> wrote: Hi
Please help, how can I interpret the following results of my EXPLAIN query ?, I can see that the query will through 18586018 rows, but what’s the meaning of cost and width?
GroupAggregate (cost=762381141.96..768375132.77 rows=18586018 width=32)
cost=762381141.96..768375132.77 means, cost of retrieving the first row is 762381141.96 and the cost of retrieving all the rows is 768375132.77. rows=18586018 means, expected number of rows as an output. width=32 means, width of each row scanned/retrieved is 32 bytes. Cost calculation formula for PostgreSQL is as follows : cost = (disk pages read * seq_page_cost) + (rows scanned * cpu_tuple_cost) The above formula may help you analyze/reduce the cost of the query.
If you do an EXPLAIN ANALYZE (sample output is below), that will further help you get more information like query completion time in milli-seconds (actual time), number of rows returned (rows) and how many iterations the query went through to get the output (loop)
Thanks, Venkata Balaji N
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