Add pg_buffercache_usage_counts() to contrib/pg_buffercache.

It was pointed out that pg_buffercache_summary()'s report of
the overall average usage count isn't that useful, and what
would be more helpful in many cases is to report totals for
each possible usage count.  Add a new function to do it like
that.  Since pg_buffercache 1.4 is already new for v16,
we don't need to create a new extension version; we'll just
define this as part of 1.4.

Nathan Bossart

Discussion: https://postgr.es/m/20230130233040.GA2800702@nathanxps13

1 files changed, 4 insertions, 0 deletions

diff --git a/contrib/pg_buffercache/sql/pg_buffercache.sql b/contrib/pg_buffercache/sql/pg_buffercache.sql
index 2e2e0a74517..944fbb1beae 100644
--- a/contrib/pg_buffercache/sql/pg_buffercache.sql
+++ b/contrib/pg_buffercache/sql/pg_buffercache.sql
@@ -10,15 +10,19 @@ select buffers_used + buffers_unused > 0,
         buffers_pinned <= buffers_used
 from pg_buffercache_summary();
 
+SELECT count(*) > 0 FROM pg_buffercache_usage_counts() WHERE buffers >= 0;
+
 -- Check that the functions / views can't be accessed by default. To avoid
 -- having to create a dedicated user, use the pg_database_owner pseudo-role.
 SET ROLE pg_database_owner;
 SELECT * FROM pg_buffercache;
 SELECT * FROM pg_buffercache_pages() AS p (wrong int);
 SELECT * FROM pg_buffercache_summary();
+SELECT * FROM pg_buffercache_usage_counts();
 RESET role;
 
 -- Check that pg_monitor is allowed to query view / function
 SET ROLE pg_monitor;
 SELECT count(*) > 0 FROM pg_buffercache;
 SELECT buffers_used + buffers_unused > 0 FROM pg_buffercache_summary();
+SELECT count(*) > 0 FROM pg_buffercache_usage_counts();