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

-----Original Message-----
From: pgsql-admin-owner(at)postgresql(dot)org
[mailto:pgsql-admin-owner(at)postgresql(dot)org] On Behalf Of Thomas Kellerer
Sent: 25 March 2015 01:05 PM
To: pgsql-admin(at)postgresql(dot)org
Subject: Re: [ADMIN] Postgres 9 : - How to interpret the EXPLAIN query
results

Khangelani Gama schrieb am 25.03.2015 um 11:28:
> 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

No. The cost is not the total time.

Quote from the manual

measured in cost units that are arbitrary, but conventionally mean disk
page fetches

In general you can _assume_ that a query with a higher cost is likely to run
longer than an equivalent query with lower costs.

If you want the runtime of each step you need to use "explain (analyze)" -
again this is documented in the manual.

Thomas

Many Thanks Thomas

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