On Fri, 27 Jun 2003 08:07:35 +0200, Andre Schubert
>Traffic data are inserted every 5 minutes with the actual datetime
>of the transaction, thatswhy the table should be physically order by time_stamp.

So I'd expect a correlation of nearly 1.  Why do your statistics show
a value of -0.479749?  A negative correlation is a sign of descending
sort order, and correlation values closer to 0 indicate poor
correspondence between column values and tuple positions.

Could this be the effect of initial data loading?  Are there any
updates or deletions in your traffic table?

>To answer Manfreds questions:
>> Andre, what hardware is this running on?  What are the values of
>> shared_buffers, random_page_cost, effective_cache_size, ... ?  Could
>> you show us the result of
>>      SELECT * FROM pg_stats
>>       WHERE tablename = "tbl_traffic" AND attname = "time_stamp";
                           ^           ^               ^          ^
Oops, these should have been single quotes.  It's too hot here these
days :-)

>sort_mem = 32000
>shared_buffers = 13000

Personally I would set them to lower values, but if you have good
reasons ...

>#effective_cache_size = 1000  # default in 8k pages

This is definitely too low.  With 512MB or more I tend to set this to
ca. 80% of available RAM.  Use top and free to find hints for good


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