Re: Intermittent buildfarm failures on wrasse

Hi,

On 2022-04-15 10:15:32 -0400, Tom Lane wrote:
> The morning's first result is that during a failing run,
> the vacuum in test_setup sees
>
> 2022-04-15 16:01:43.064 CEST [4436:75] pg_regress/test_setup LOG: statement: VACUUM ANALYZE tenk1;
> 2022-04-15 16:01:43.064 CEST [4436:76] pg_regress/test_setup LOG: vacuuming "regression.public.tenk1"
> 2022-04-15 16:01:43.064 CEST [4436:77] pg_regress/test_setup STATEMENT: VACUUM ANALYZE tenk1;
> 2022-04-15 16:01:43.071 CEST [4436:78] pg_regress/test_setup LOG: finished vacuuming "regression.public.tenk1": index scans: 0
> pages: 0 removed, 345 remain, 345 scanned (100.00% of total)
> tuples: 0 removed, 10000 remain, 0 are dead but not yet removable
> removable cutoff: 724, older by 26 xids when operation ended
> index scan not needed: 0 pages from table (0.00% of total) had 0 dead item identifiers removed
> avg read rate: 2.189 MB/s, avg write rate: 2.189 MB/s
> buffer usage: 695 hits, 2 misses, 2 dirtied
> WAL usage: 1 records, 0 full page images, 188 bytes
> system usage: CPU: user: 0.00 s, system: 0.00 s, elapsed: 0.00 s
> 2022-04-15 16:01:43.071 CEST [4436:79] pg_regress/test_setup STATEMENT: VACUUM ANALYZE tenk1;

The horizon advancing by 26 xids during tenk1's vacuum seems like quite
a bit, given there's no normal concurrent activity during test_setup.

> In fact, right after initdb pg_controldata shows
> Latest checkpoint's NextXID: 0:724
> Latest checkpoint's oldestXID: 716

So that's the xmin that e.g. the autovac launcher ends up with during
start...

If I make get_database_list() sleep for 5s within the scan, I can
reproduce on x86-64.

Greetings,

Andres Freund