Re: 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.

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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