Re: [HACKERS] Block level parallel vacuum WIP

On Sat, Jan 7, 2017 at 7:18 AM, Claudio Freire <klaussfreire@gmail.com> wrote:
> On Fri, Jan 6, 2017 at 2:38 PM, Masahiko Sawada <sawada.mshk@gmail.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