From: | Alexander Kuzmenkov <a(dot)kuzmenkov(at)postgrespro(dot)ru> |
---|---|
To: | Dilip Kumar <dilipbalaut(at)gmail(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com> |
Cc: | pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Proposal: Improve bitmap costing for lossy pages |
Date: | 2017-10-06 12:38:52 |
Message-ID: | 9daaf288-e67f-f349-965f-3a8c6e0819ae@postgrespro.ru |
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Thread: | |
Lists: | pgsql-hackers |
> 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
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