Horton

Re: [HACKERS] Execution time.

Shiby Thomas <sthomas@cise.ufl.edu>

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From: Shiby Thomas <sthomas@cise.ufl.edu>
To: The Hermit Hacker <scrappy@hub.org>
Cc: "Vadim B. Mikheev" <vadim@sable.krasnoyarsk.su>, pgsql-hackers@postgreSQL.org
Date: 1998-02-04T18:07:01Z
Lists: pgsql-hackers 
=> > Is the size of the hash bucket dependent on the number of buffers available ?
=> > If so, with -B 30000, it might create huge hash buckets and hence the
=> > hash join could degenerate to a nested loops join. Is that possible -- just
=> > checking. What could be good values for -B and -S. The largest table I am
=> > joining is about 60M
=> 
=> 	My production server runs with a -B 256, and a -S 10240
=> 
=> 
With less buffers, it is giving "hash table out of memory" error.
I ran with -B 512

AGG :c=435416.5312 :s=0 :w=0 
   l: GROUP :c=435416.5312 :s=0 :w=0 
      l: SORT :c=435416.5312 :s=0 :w=0 
         l: HASHJOIN :c=435416.5312 :s=305715 :w=16 
            l: SEQSCAN :c=36107.7500 :s=917144 :w=8  ( t1 )
            r: HASH :c=0.0000 :s=0 :w=0 
               l: SEQSCAN :c=36107.7500 :s=917144 :w=8  ( t1 )
ERROR:  hash table out of memory. Use -B parameter to increase buffers.