From: | Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> |
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To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | PostgreSQL-development <pgsql-hackers(at)postgreSQL(dot)org> |
Subject: | subquery performance and EXISTS |
Date: | 1999-12-29 14:11:51 |
Message-ID: | 199912291411.JAA02236@candle.pha.pa.us |
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Lists: | pgsql-hackers |
I am writing the subquery chapter of the book. Tom, you once mentioned
you could get subqueries to use HASH joins, but you didn't because
someone said it may a run out of memory.
I would suggest that if it is that large a subquery, our nested loop
handling will take forever, so would never finish anyway, unless the
outer query has only a few rows.
Tom, does it still look easy to change, and if so, can you change it to
hash? I know the real fix is for multiple target lists.
I would rather not have to go mention a serious performance workaround
in the book, because the limitation would be published perhaps for many
years.
--
Bruce Momjian | http://www.op.net/~candle
maillist(at)candle(dot)pha(dot)pa(dot)us | (610) 853-3000
+ If your life is a hard drive, | 830 Blythe Avenue
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026
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