Re: Sample rate added to pg_stat_statements

> All the changes mentioned above are included in the v13 patch. Since the
> patch status is 'Ready for Committer,' I believe it is now better for
> upstream inclusion, with improved details in tests and documentation. Do
> you have any further suggestions?

I am not quite clear on the sample_1.out. I do like the idea of separating
the sample tests, but I was thinking of something a bit more simple.
What do you think of my attached, sampling.sql, test? It tests sample
rate in both
simple and extended query protocols and for both top level and
nested levels?

> If anyone has the capability to run this benchmark on machines with more
> CPUs or with different queries, it would be nice. I’d appreciate any
> suggestions or feedback.

I wanted to share some additional benchmarks I ran as well
on a r8g.48xlarge ( 192 vCPUs, 1,536 GiB of memory) configured
with 16GB of shared_buffers. I also attached the benchmark.sh
script used to generate the output.
The benchmark is running the select-only pgbench workload,
so we have a single heavily contentious entry, which is the
worst case.

The test shows that the spinlock (SpinDelay waits)
becomes an issue at high connection counts and will
become worse on larger machines. A sample_rate going from
1 to .75 shows a 60% improvement; but this is on a single
contentious entry. Most workloads will likely not see this type
of improvement. I also could not really observe
this type of difference on smaller machines ( i.e. 32 vCPUs),
as expected.

## init
pgbench -i -s500

### 192 connections
pgbench -c192 -j20 -S -Mprepared -T120 --progress 10

sample_rate = 1
tps = 484338.769799 (without initial connection time)
waits
-----
11107 SpinDelay
9568 CPU
929 ClientRead
13 DataFileRead
3 BufferMapping

sample_rate = .75
tps = 909547.562124 (without initial connection time)
waits
-----
12079 CPU
4781 SpinDelay
2100 ClientRead

sample_rate = .5
tps = 1028594.555273 (without initial connection time)
waits
-----
13253 CPU
3378 ClientRead
174 SpinDelay

sample_rate = .25
tps = 1019507.126313 (without initial connection time)
waits
-----
13397 CPU
3423 ClientRead

sample_rate = 0
tps = 1015425.288538 (without initial connection time)
waits
-----
13106 CPU
3502 ClientRead

### 32 connections
pgbench -c32 -j20 -S -Mprepared -T120 --progress 10

sample_rate = 1
tps = 620667.049565 (without initial connection time)
waits
-----
1782 CPU
560 ClientRead

sample_rate = .75
tps = 620663.131347 (without initial connection time)
waits
-----
1736 CPU
554 ClientRead

sample_rate = .5
tps = 624094.688239 (without initial connection time)
waits
-----
1741 CPU
648 ClientRead

sample_rate = .25
tps = 628638.538204 (without initial connection time)
waits
-----
1702 CPU
576 ClientRead

sample_rate = 0
tps = 630483.464912 (without initial connection time)
waits
-----
1638 CPU
574 ClientRead

Regards,

Sami