On Mar 17, 2007, at 10:33 PM, Luke Lonergan wrote:

Wow, nice!

Can you tell us:
- how big is the table
- cardinality of the column
- how big is the index in each case
- how much memory on the machine
- query and explain analyze

All I changed, was the 400k to 150k
512MB of ram, as I said earlier. And it is running 64bit kernel, 32bit user-land on linux 2.6.20

query and explain is going to run for a while, so I'll leave it - as it is going to be the same on other machines (much faster ones). postgres=# select pg_size_pretty( pg_relation_size ( 'narrowtable_index' ) );
321 MB
(1 row)

postgres=# select pg_size_pretty( pg_relation_size ( 'narrowtable2_clustered_index' ) );
3960 kB
(1 row)

(so there's quite a difference).

Judging from noises coming out of machine, there was pretty loads of I/O activity. and funny enough, one CPU was stucked on 'wait' up to 80% most of the time.

the 'cardinality', as I guess, uniqueness is the same as intended in original test. Like I said, only table size was changed.

select count(distinct key) from narrowtable; and select count(*) from narrowtable; are the same - 15000000


Grzegorz Jaskiewicz

C/C++ freelance for hire

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