RE: reloption to prevent VACUUM from truncating empty pages at the end of relation

From: Fujii Masao [mailto:masao(dot)fujii(at)gmail(dot)com]
> a very long time before accessing to the relation. Which would cause the
> response-time spikes, for example, I observed such spikes several times
> on
> the server with shared_buffers = 300GB while running the benchmark.

FYI, a long transaction took about 900 ms, while the average transaction response time was 150 ms or so. (I'm working with Fujii-san in this performance benchmark.)

> Therefore, I'm thinking to propose $SUBJECT and enable it to avoid such
> spikes
> for that relation.

How about an integer variable to replace the following?

#define REL_TRUNCATE_FRACTION 16

> Also, first of all, if other transactions need to extend the relation
> (i.e., need new pages) as soon as VACUUM truncates the empty pages at the
> end,
> that truncation would not be so helpful for performance. In this case,
> the truncation and extension of the relation are unnecessarily repeated,
> which would decrease the performance. So, to alleviate this situation,
> $SUBJECT is useful, I think.

I wonder if fillfactor=50 would alleviate this situation.

Regards
Takayuki Tsunakawa