From: | Kovacs Zoltan <kovacsz(at)pc10(dot)radnoti-szeged(dot)sulinet(dot)hu> |
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To: | pgsql-hackers(at)postgresql(dot)org |
Subject: | slow UNIONing |
Date: | 2001-09-18 13:52:28 |
Message-ID: | Pine.LNX.4.21.0109181548210.3295-100000@pc10.radnoti-szeged.sulinet.hu |
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Lists: | pgsql-hackers |
I experienced that UNIONs in 7.1.1 are rather slow:
tir=# explain (select nev from cikk) union (select tevekenyseg from log);
NOTICE: QUERY PLAN:
Unique (cost=667.63..687.18 rows=782 width=12)
-> Sort (cost=667.63..667.63 rows=7817 width=12)
-> Append (cost=0.00..162.17 rows=7817 width=12)
-> Subquery Scan *SELECT* 1 (cost=0.00..28.16 rows=1316 width=12)
-> Seq Scan on cikk (cost=0.00..28.16 rows=1316 width=12)
-> Subquery Scan *SELECT* 2 (cost=0.00..134.01 rows=6501 width=12)
-> Seq Scan on log (cost=0.00..134.01 rows=6501 width=12)
Of course a simple SELECT is fast:
tir=# explain select nev from cikk;
NOTICE: QUERY PLAN:
Seq Scan on cikk (cost=0.00..28.16 rows=1316 width=12)
For me it seems to be slow due to the sorting. Is this right?
Is this normal at all? Is it possible to make it faster?
TIA, Zoltan
--
Kov\'acs, Zolt\'an
kovacsz(at)pc10(dot)radnoti-szeged(dot)sulinet(dot)hu
http://www.math.u-szeged.hu/~kovzol
ftp://pc10.radnoti-szeged.sulinet.hu/home/kovacsz
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