Re: stats.sql might fail due to shared buffers also used by parallel tests

Hello Kuroda-san and Takatsuka-san,

24.07.2025 03:49, TAKATSUKA Haruka wrote:
> {snip}
>> Maybe you could try tools.syncTime = "0" by any chance?
> It has been already tools.syncTime = "0" so far.
> I confirmed the following GUI setting.
> ...

23.07.2025 09:15, Hayato Kuroda (Fujitsu) wrote:
> It looks like for me that we measured the execution time of the function in
> millisecond but it was "zero", right?

Yes, my understanding is the same.

>> So I think we could observe such anomalies if, say, the OS kernel can't
>> read system clock in time (stalls for a millisecond when accessing it)...
> I also feel like that. But if so, how should we fix tests? We must remove all
> stuff which assumes the time is monotonic?

From what Takatsuka-san shared on hamerkop's configuration, I still
suspect there could be some platform specifics there. I've found another
interesting reading on the subject, which describes effects of CPU
pressure and mentions other low-level parameters, e. g.
monitor_control.virtual_rdtsc: [1].

Probably there could be some experiments performed there to measure the
maximum timer resolution (e. g. with a simple program attached).

I also observed a failure of pg_stat_statements on ARMv7 device in the past:
--- .../contrib/pg_stat_statements/expected/entry_timestamp.out 2024-04-11 07:20:32.563588101 +0300
+++ .../contrib/pg_stat_statements/results/entry_timestamp.out 2024-04-15 11:16:00.217396694 +0300
@@ -45,7 +45,7 @@
 WHERE query LIKE '%STMTTS%';
  total | minmax_plan_zero | minmax_exec_zero | minmax_stats_since_after_ref | stats_since_after_ref
 -------+------------------+------------------+------------------------------+-----------------------
-     2 |                0 |                0 |                            0 |                     0
+     2 |                0 |                1 |                            0 |                     0
 (1 row)

with clocksource =  32k_counter, which gave me the maximum resolution
0.030517 sec.

So if to choose fixing tests, then it's not clear to me, what lowest timer
resolution to consider acceptable.

[1] https://www.vmware.com/docs/vmware_timekeeping

Best regards,
Alexander