Re: Optimize query for listing un-read messages

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På torsdag 01. mai 2014 kl. 20:35:07, skrev Jochem Berndsen <jochem@xxxxxxxxxx>:

Hi Andreas,

[New to this list, forgive my ignorance.]
[snip]
I'm getting better performance with:

SELECT
m.id AS message_id,
1 AS person_id,
FALSE AS is_read,
m.subject
FROM message m
WHERE 1 = 1
AND NOT EXISTS(SELECT
     *
     FROM message_property pr
     WHERE pr.message_id = m.id AND pr.person_id = 1 AND pr.is_read);

You then lose the distinction between message_property with is_read =
FALSE, and nonexistent message_property for the message row.

If that is essential, I'm getting a roughly 2x speedup on my non-tuned
PostgreSQL with:
  SELECT
     m.id                          AS message_id,
     prop.person_id,
     coalesce(prop.is_read, FALSE) AS is_read,
     m.subject
FROM message m
     LEFT OUTER JOIN message_property prop ON prop.message_id = m.id AND
prop.person_id = 1
WHERE not coalesce(prop.is_read, false);
 
 
Hi Jochem,
 
Thansk for looking at it. I'm still seing ~500ms being spent and I was hoping for a way to do this using index so one could achieve 1-10ms, but maybe that's impossible given the schema?
 
Is there a way to design an equivalent  schema to achieve <10ms execution-time?
 
--
Andreas Jospeh Krogh
CTO / Partner - Visena AS
Mobile: +47 909 56 963
andreas@xxxxxxxxxx
www.visena.com
 

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