Re: Block level parallel vacuum WIP

On Sat, Jan 7, 2017 at 7:18 AM, Claudio Freire <klaussfreire(at)gmail(dot)com> wrote:
> On Fri, Jan 6, 2017 at 2:38 PM, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
>> table_size | indexes | parallel_degree | time
>> ------------+---------+-----------------+----------
>> 6.5GB | 0 | 1 | 00:00:14
>> 6.5GB | 0 | 2 | 00:00:02
>> 6.5GB | 0 | 4 | 00:00:02
>
> Those numbers look highly suspect.
>
> Are you sure you're not experiencing caching effects? (ie: maybe you
> ran the second and third vacuums after the first, and didn't flush the
> page cache, so the table was cached)
>
>> 6.5GB | 2 | 1 | 00:02:18
>> 6.5GB | 2 | 2 | 00:00:38
>> 6.5GB | 2 | 4 | 00:00:46
> ...
>> 13GB | 0 | 1 | 00:03:52
>> 13GB | 0 | 2 | 00:00:49
>> 13GB | 0 | 4 | 00:00:50
> ..
>> 13GB | 2 | 1 | 00:12:42
>> 13GB | 2 | 2 | 00:01:17
>> 13GB | 2 | 4 | 00:02:12
>
> These would also be consistent with caching effects

Since I ran vacuum after updated all pages on table, I thought that
all data are in either shared buffer or OS cache. But anyway, I
measured it at only one time so this result is not accurate. I'll test
again and measure it at some times.

Regards,

--
Masahiko Sawada
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center