> I mean, that the issue is indeed affected by the order of rows in the
> table. Random heap access patterns result in sparse bitmap heap scans,
> whereas less random heap access patterns result in denser bitmap heap
> scans. Dense scans have large portions of contiguous fetches, a
> pattern that is quite adversely affected by the current prefetch
> mechanism in linux.
>
Thanks for your input.
How can I test a sparse bitmap scan? Can you think of any SQL commands
which would generate data and run such scans?
Would a bitmap scan over expression index ((aid%1000)=0) do a sparse
bitmap scan?
Regards,
Vitaliy