Re: optimizing vacuum truncation scans

On Thu, Jul 9, 2015 at 5:36 PM, Haribabu Kommi <kommi(dot)haribabu(at)gmail(dot)com> wrote:
>
> I will do some performance tests and send you the results.

Here are the performance results tested on my machine.

Head vm patch vm+prefetch patch

First vacuum 120sec <1sec <1sec
second vacuum 180 sec 180 sec 30 sec

I did some modifications in the code to skip the vacuum truncation by
the first vacuum command.
This way I collected the second vacuum time taken performance.

I just combined your vm and prefetch patch into a single patch
vm+prefetch patch without a GUC.
I kept the prefetch as 32 and did the performance test. I chosen
prefetch based on the current
buffer access strategy, which is 32 for vacuum presently instead of an
user option.
Here I attached the modified patch with both vm+prefetch logic.

I will do some tests on a machine with SSD and let you know the
results. Based on these results,
we can decide whether we need a GUC or not? based on the impact of
prefetch on ssd machines.

Regards,
Hari Babu
Fujitsu Australia