[PATCH] psql: \dn+ to show size of each schema..

\db+ and \l+ show sizes of tablespaces and databases, so I was surprised in the
past that \dn+ didn't show sizes of schemas. I would find that somewhat
convenient, and I assume other people would use it even more useful.

\db+ and \l+ seem to walk the filesystem, and this is distinguished from those
cases. (Also, schemas are per-DB, not global).

Maybe it's an issue if \dn+ is slow and expensive, since that's how to display
ACL. But \db+ has the same issue. Maybe there should be a \db++ and \dn++ to
allow \dn+ to showing the ACL but not the size.

pg_relation_size() only includes one fork, and the other functions include
toast, which should be in its separate schema, so it has to be summed across
forks.

postgres=# \dnS+
child | postgres | | | 946 MB
information_schema | postgres | postgres=UC/postgres+| | 88 kB
| | =U/postgres | |
pg_catalog | postgres | postgres=UC/postgres+| system catalog schema | 42 MB
| | =U/postgres | |
pg_toast | postgres | | reserved schema for TOAST tables | 3908 MB
public | postgres | postgres=UC/postgres+| standard public schema | 5627 MB
| | =UC/postgres | |

From c2d68eb54f785c759253d4100460aa1af9cbc676 Mon Sep 17 00:00:00 2001
From: Justin Pryzby <pryzbyj(at)telsasoft(dot)com>
Date: Tue, 13 Jul 2021 21:25:48 -0500
Subject: [PATCH] psql: \dn+ to show size of each schema..

See also: 358a897fa, 528ac10c7
---
src/bin/psql/describe.c | 5 +++++
1 file changed, 5 insertions(+)

diff --git a/src/bin/psql/describe.c b/src/bin/psql/describe.c
index 2abf255798..6b9b6ea34a 100644
--- a/src/bin/psql/describe.c
+++ b/src/bin/psql/describe.c
@@ -5036,6 +5036,11 @@ listSchemas(const char *pattern, bool verbose, bool showSystem)
appendPQExpBuffer(&buf,
",\n pg_catalog.obj_description(n.oid, 'pg_namespace') AS \"%s\"",
gettext_noop("Description"));
+
+ appendPQExpBuffer(&buf,
+ ",\n (SELECT pg_catalog.pg_size_pretty(sum(pg_relation_size(oid,fork))) FROM pg_catalog.pg_class c,\n"
+ " (VALUES('main'),('fsm'),('vm'),('init')) AS fork(fork) WHERE c.relnamespace = n.oid) AS \"%s\"",
+ gettext_noop("Size"));
}

appendPQExpBufferStr(&buf,
--
2.17.0