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

Hi Jan,

Thanks for testing v2 and for the additional review.

Attached is v3. I split the changes into two patches:

1. Change the applicable object-to-pg_namespace joins from LEFT JOIN to JOIN.
2. Add appendSystemSchemaFilter() and use it in the affected describe queries.

I also wrapped both commit messages at around 75 characters.

I left the pg_toast optimization out of this series, as suggested, so it can
be handled separately without expanding the scope of this patch.

The series is rebased onto current master (792094a5ce8). make check-world
passes for all suites enabled in my local build. TAP tests were not enabled
because IPC::Run is unavailable locally.

Best regards,
Xiaoyu