From: Kevin Grittner <kgrittn@mail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Pavan Deolasee <pavan.deolasee@gmail.com>
Cc: Amitabh Kant <amitabhkant@gmail.com>
Cc: pgsql-performance <pgsql-performance@postgresql.org>
Subject: Re: Limit & offset effect on query plans
Date: Thu, 13 Dec 2012 12:07:00 -0500
Message-ID: <20121213170700.80080@gmx.com> (raw)
List-Unsubscribe: <mailto:majordomo@postgresql.org?body=unsub%20pgsql-performance>
Tom Lane wrote:
> "Kevin Grittner" <kgrittn@mail.com> writes:
>> I ran some quick tests on my i7 under Linux. Plan time was
>> increased by about 40 microseconds (based on EXPLAIN runtime)
>> and added a limit node to the plan. Execution time on a SELECT *
>> FROM tenk1 in the regression database went up by 1.35 ms on
>> fully cached runs.
>
> 1.35ms out of what?
Without the limit node the runtimes (after "priming" the cache)
were:
1.805, 2.533
1.805, 2.495
1.800, 2.446
1.818, 2.470
1.804, 2.502
The first time for each run is "Total runtime" reported by EXPLAIN,
the second is what psql reported from having \timing on.
With the limit node:
3.237, 3.914
3.243, 3.918
3.263, 4.010
3.265, 3.943
3.272, 3.953
I eyeballed that in the console window and said 1.35 based on rough
in-my-head calculations, although with it laid out in a nicer
format, I think I was a little low.
-Kevin
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Cc: kgrittn@mail.com, tgl@sss.pgh.pa.us, pavan.deolasee@gmail.com, amitabhkant@gmail.com
Subject: Re: Limit & offset effect on query plans
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