pg.ddx.io pgsql-sql@postgresql.org mailing list archive
help / color / mirror / Atom feedmaterialize
2+ messages / 2 participants
[nested] [flat]
* materialize
@ 2007-11-26 21:17 Ehab Galal <ehabgalal123@hotmail.com>
0 siblings, 1 reply; 2+ messages in thread
From: Ehab Galal @ 2007-11-26 21:17 UTC (permalink / raw)
To: pgsql-sql
Greetings,
I was wondering why do we need the Materialize node in the plan below when i explain a query?
1: QUERY PLAN = "Nested Loop (cost=10.99..24.34 rows=1 width=846)" (typeid = 25, len = -1, typmod = -1, byval = f)
----
1: QUERY PLAN = " Join Filter: (("inner".cover)::text = ("outer".cover)::text)" (typeid = 25, len = -1, typmod = -1, byval = f)
----
1: QUERY PLAN = " -> Index Scan using idx_cover_ftn_ on c_cover_ftn (cost=0.00..9.30 rows=2 width=86)" (typeid = 25, len = -1, typmod = -1, byval = f)
----
1: QUERY PLAN = " Index Cond: (username = 'user1'::name)" (typeid = 25, len = -1, typmod = -1, byval = f)
----
1: QUERY PLAN = " -> Materialize (cost=10.99..11.89 rows=90 width=842)" (typeid = 25, len = -1, typmod = -1, byval = f)
----
1: QUERY PLAN = " -> Seq Scan on books (cost=0.00..10.90 rows=90 width=842)" (typeid = 25, len = -1, typmod = -1, byval = f)
----
Thanks,
Ehab
_________________________________________________________________
Your smile counts. The more smiles you share, the more we donate. Join in.
www.windowslive.com/smile?ocid=TXT_TAGLM_Wave2_oprsmilewlhmtagline=
^ permalink raw reply [nested|flat] 2+ messages in thread
* Re: materialize
@ 2007-11-26 21:53 Tom Lane <tgl@sss.pgh.pa.us>
parent: Ehab Galal <ehabgalal123@hotmail.com>
0 siblings, 0 replies; 2+ messages in thread
From: Tom Lane @ 2007-11-26 21:53 UTC (permalink / raw)
To: Ehab Galal <ehabgalal123@hotmail.com>; +Cc: pgsql-sql
Ehab Galal <ehabgalal123@hotmail.com> writes:
> I was wondering why do we need the Materialize node in the plan below when i explain a query?
It's cheaper to scan a materialized rowset many times than a raw table
--- we don't need to re-access shared memory nor re-check row visibility.
regards, tom lane
^ permalink raw reply [nested|flat] 2+ messages in thread
end of thread, other threads:[~2007-11-26 21:53 UTC | newest]
Thread overview: 2+ messages (download: mbox mbox.gz follow: Atom feed)
-- links below jump to the message on this page --
2007-11-26 21:17 materialize Ehab Galal <ehabgalal123@hotmail.com>
2007-11-26 21:53 ` Tom Lane <tgl@sss.pgh.pa.us>
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox