Re: Many of psql's describe functions bloat cache / waste mem

Hi Jan,

Thanks for the detailed review and for confirming the memory reduction.

Attached is v2. I followed your suggestions:

- introduced appendSystemSchemaFilter() and reused it in the
describe.c queries that exclude pg_catalog and information_schema,
including \df and \do;
- changed the corresponding object-to-pg_namespace LEFT JOINs to JOIN
where the namespace is mandatory;
- removed the TAP test from v1, since checking the generated SQL text
cannot guarantee planner clause evaluation order.

The filter still uses an uncorrelated pg_namespace subquery, so it
becomes an InitPlan. The ARRAY(...) / <> ALL form also continues to
work when information_schema is absent.

I rebased v2 onto current master (3b120b1e94d). make check-world
passes for all suites enabled in my local build. TAP tests were not
enabled because IPC::Run is not available locally. I also manually
checked the affected psql commands, including \df and \do, and
confirmed the expected plan shape and CacheMemoryContext behavior.

Please let me know what you think.

Best regards,
Xiaoyu