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
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http://www.math.u-szeged.hu/~kovzol
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