Improve handling of prune/no-prune decisions by storing a page's oldest

unpruned XMAX in its header.  At the cost of 4 bytes per page, this keeps us
from performing heap_page_prune when there's no chance of pruning anything.
Seems to be necessary per Heikki's preliminary performance testing.

1 files changed, 2 insertions, 1 deletions

diff --git a/contrib/pageinspect/pageinspect.sql.in b/contrib/pageinspect/pageinspect.sql.in
index 40b75dcbc02..4821f8c3a3e 100644
--- a/contrib/pageinspect/pageinspect.sql.in
+++ b/contrib/pageinspect/pageinspect.sql.in
@@ -20,7 +20,8 @@ CREATE OR REPLACE FUNCTION page_header(IN page bytea,
     OUT upper smallint,
     OUT special smallint,
     OUT pagesize smallint,
-    OUT version smallint)
+    OUT version smallint,
+    OUT prune_xid xid)
 AS 'MODULE_PATHNAME', 'page_header'
 LANGUAGE C STRICT;