Re: Postgres 9 : - How to interpret the EXPLAIN query results

*From:* Raghavendra [mailto:raghavendra(dot)rao(at)enterprisedb(dot)com]
*Sent:* 25 March 2015 12:04 PM
*To:* Khangelani Gama
*Cc:* pgsql-admin
*Subject:* Re: [ADMIN] Postgres 9 : - How to interpret the EXPLAIN query
results

On Wed, Mar 25, 2015 at 1:30 PM, Khangelani Gama <kgama(at)argility(dot)com> 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)

​Its like ..

​NodeType (cost=startup-cost..total-cost rows=plan rows width=bytes per-row)

Documentation has briefed well on the explain output. Here's example.

Thanks to all, but if this total cost is the total time it will take to
retrieve the output then is it in minutes or milliseconds? If it’s in
milliseconds does it mean that it take about 213 hrs for a total of
768375132.77

postgres=# explain select * from foo;

QUERY PLAN

-----------------------------------------------------------

Seq Scan on foo (cost=0.00..5770.01 rows=400001 width=4)

(1 row)

postgres=# EXPLAIN (FORMAT JSON) SELECT * FROM foo;

QUERY PLAN

--------------------------------

[ +

{ +

"Plan": { +

"Node Type": "Seq Scan",+

"Relation Name": "foo", +

"Alias": "foo", +

"Startup Cost": 0.00, +

"Total Cost": 5770.01, +

"Plan Rows": 400001, +

"Plan Width": 4 +

} +

} +

]

(1 row)

http://www.postgresql.org/docs/9.3/static/sql-explain.html

---

Regards,

Raghavendra

EnterpriseDB Corporation

Blog: http://raghavt.blogspot.com/​

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