Re: Proposal: Improve bitmap costing for lossy pages

> Analysis: The estimated value of the lossy_pages is way higher than
> its actual value and reason is that the total_pages calculated by the
> "Mackert and Lohman formula" is not correct.

I think the problem might be that the total_pages includes cache effects
and rescans. For bitmap entries we should use something like relation
pages * selectivity.

Meanwhile, I ran TPC-H briefly with the v3 patch: scale factor 25, 2
workers, SSD storage.
It shows significant improvement on 4MB work_mem and no change on 2GB.

Here are the results (execution time in seconds, average of 5 runs):
work_mem 4MB 2GB
Query master patch master patch
4 179 174 168 167
5 190 168 155 156
6 280 87 227 229
8 197 114 179 172
10 269 227 190 192
14 110 108 106 105

--
Alexander Kuzmenkov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company