| From: | Andy Fan <zhihuifan1213(at)163(dot)com> |
|---|---|
| To: | David Rowley <dgrowleyml(at)gmail(dot)com> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Maxim Boguk <maxim(dot)boguk(at)gmail(dot)com>, pgsql-bugs(at)lists(dot)postgresql(dot)org |
| Subject: | Re: BUG #18588: Cannot force/let database use parallel execution in simple case. |
| Date: | 2024-08-23 01:47:45 |
| Message-ID: | 87h6bcrovy.fsf@163.com |
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| Lists: | pgsql-bugs |
> .. I think Maxim might need to try tweaking effective_cache_size. ..
I'm right now doing some troubleshooting for Bitmap Index Scan vs Index
Scan and effective_cache_size caught my attention. I want to take this
chance to confirm my understanding about this parameter.
1. By design, effective_cache_size should not less than shared_buffer
since file-system cache should be considered as well.
2. Mackert and Lohman's algorithm in index_pages_fetched looks doesn't
consider the number of concurrency? so if we have N sessions to access N
different small relations, but sum_of_n_relations is larger than
effective_cache_size, would the index_pages_fetched figure out a much
smaller value than the fact?
--
Best Regards
Andy Fan
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