Re: Optimization for lazy_scan_heap

On Tue, Sep 6, 2016 at 11:13 PM, Masahiko Sawada <sawada.mshk@gmail.com> wrote:
> I understood, thank you.
>
> I've measured the performance benefit of this patch by following steps.
> 1. Create very large table and set all-visible flag to all blocks.
> 2. Measure the execution time of vacuum that skips to scan all heap pages.
>
> * 1TB Table(visibility map size is 32MB)
> HEAD : 11012.274 ms (00:11.012)
> Patched : 6742.481 ms (00:06.742)
>
> * 8TB Table(visibility map size is 64MB)
> HEAD : 69886.605 ms (01:09.887)
> Patched : 35562.131 ms (00:35.562)
>
> * 32TB Table(visibility map size is 258MB)
> HEAD: 265901.096 ms (04:25.901)
> Patched: 131779.082 ms (02:11.779)
>
> Since current HEAD could scan visibility map twice, the execution time
> of Patched is approximately half of HEAD.
> But when table is several hundreds gigabyte, performance benefit would
> not be large.

Wow, those are surprisingly good results.  Interesting.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company