Date: Fri, 19 Mar 2010 16:16:38 -0500
From: Kenneth Marshall <ktm@rice.edu>
To: Yeb Havinga <yebhavinga@gmail.com>
Cc: Matthew Wakeling <matthew@flymine.org>,
	Bruce Momjian <bruce@momjian.us>, pgsql-performance@postgresql.org
Subject: Re: GiST index performance
Message-ID: <20100319211638.GI1218@it.is.rice.edu>
References: <201002252342.o1PNgtG07127@momjian.us>
	<alpine.DEB.2.00.1003151548180.1887@aragorn.flymine.org>
	<4B9FAF4B.20907@gmail.com> <4BA0A036.1070508@gmail.com>
	<4BA3A6C6.80406@gmail.com> <4BA3DCA1.2010808@gmail.com>
	<4BA3E35A.1000905@gmail.com>
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Hi Yeb,

I have not looked at the gist code, but would it be possible to
make virtual pages that have a size that is 1/power-of-2 * blocksize.
Then the leaf node could be 1/8 or even 1/16 the size of the full
pagesize.

Regards,
Ken

On Fri, Mar 19, 2010 at 09:49:30PM +0100, Yeb Havinga wrote:
> Yeb Havinga wrote:
>>
>> Since the gistpagesize is derived from the database blocksize, it might be 
>> wise to set the blocksize low for this case, I'm going to play with this a 
>> bit more.
> Ok, one last mail before it turns into spam: with a 1KB database blocksize, 
> the query now runs in 30 seconds (original 70 on my machine, shared buffers 
> 240MB).
> The per inner loop access time now 24 microsecs compared to on my machine 
> original 74 microsecs with 8KB size and 8 for the btree scan. Not a bad 
> speedup with such a simple parameter :-)
>
> postgres=# EXPLAIN ANALYSE SELECT * FROM a, b WHERE a.a BETWEEN b.b AND b.b 
> + 2;
>                                                        QUERY PLAN           
>                                              
> ---------------------------------------------------------------------------------------------------------------------------
> Nested Loop  (cost=0.00..4169159462.20 rows=111109777668 width=8) (actual 
> time=0.184..29540.355 rows=2999997 loops=1)
>   ->  Seq Scan on b  (cost=0.00..47037.62 rows=999962 width=4) (actual 
> time=0.024..1783.484 rows=1000000 loops=1)
>   ->  Index Scan using a_a on a  (cost=0.00..2224.78 rows=111114 width=4) 
> (actual time=0.021..0.024 rows=3 loops=1000000)
>         Index Cond: ((a.a >= b.b) AND (a.a <= (b.b + 2)))
> Total runtime: 30483.303 ms
> (5 rows)
>
>
> postgres=# select gist_stat('a_a');
>                 gist_stat                 
> -------------------------------------------
> Number of levels:          5             +
> Number of pages:           47618         +
> Number of leaf pages:      45454         +
> Number of tuples:          1047617       +
> Number of invalid tuples:  0             +
> Number of leaf tuples:     1000000       +
> Total size of tuples:      21523756 bytes+
> Total size of leaf tuples: 20545448 bytes+
> Total size of index:       48760832 bytes+
> (1 row)
>
>
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