define pg_structiszero(addr, s, r)

Hi hackers,

There is some places where we check that a struct is full of zeroes:

pgstat_report_bgwriter()
pgstat_report_checkpointer()
pgstat_relation_flush_cb()

Indeed that's the way we check if there is pending statistics to flush/report.

The current code is like (taking pgstat_relation_flush_cb() as an example):

"
static const PgStat_TableCounts all_zeroes;
.
.
if (memcmp(&lstats->counts, &all_zeroes,
          sizeof(PgStat_TableCounts)) == 0)
.
.
"

The static declaration is not "really" related to the purpose of the function
it is declared in. It's there "only" to initialize a memory area with zeroes 
and to use it in the memcmp.

I think it would make sense to "hide" all of this in a new macro, so please find
attached a patch proposal doing so (Andres suggested something along those lines
in [1] IIUC).

The macro is created in pgstat_internal.h as it looks like that "only" the 
statistics related code would benefit of it currently (could be moved to other
header file later on if needed).

[1]: https://www.postgresql.org/message-id/20230105002733.ealhzubjaiqis6ua%40awork3.anarazel.de

Looking forward to your feedback,

Regards,

-- 
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com