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
