Re: Optimize query for listing un-read messages

På torsdag 01. mai 2014 kl. 20:35:07, skrev Jochem Berndsen <jochem(at)functor(dot)nl
<mailto:jochem(at)functor(dot)nl>>:
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(at)visena(dot)com <mailto:andreas(at)visena(dot)com> www.visena.com
<https://www.visena.com> <https://www.visena.com>