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.

3 files changed, 12 insertions, 10 deletions

diff --git a/contrib/pageinspect/README.pageinspect b/contrib/pageinspect/README.pageinspect
index 88cc0209549..fc4991db641 100644
--- a/contrib/pageinspect/README.pageinspect
+++ b/contrib/pageinspect/README.pageinspect
@@ -23,14 +23,14 @@ only by superusers.
 
     A page image obtained with get_raw_page should be passed as argument:
 
-        test=# SELECT * FROM page_header(get_raw_page('pg_class',0));
-           lsn    | tli | flags | lower | upper | special | pagesize | version
-        ----------+-----+-------+-------+-------+---------+----------+---------
-         0/3C5614 |   1 |     1 |   216 |   256 |    8192 |     8192 |       4
+        regression=# SELECT * FROM page_header(get_raw_page('pg_class',0));
+            lsn    | tli | flags | lower | upper | special | pagesize | version | prune_xid 
+        -----------+-----+-------+-------+-------+---------+----------+---------+-----------
+         0/24A1B50 |   1 |     1 |   232 |   368 |    8192 |     8192 |       4 |         0
         (1 row)
 
-    The returned columns correspond to the fields in the PageHeaderData-struct,
-    see src/include/storage/bufpage.h for more details.
+    The returned columns correspond to the fields in the PageHeaderData struct.
+    See src/include/storage/bufpage.h for details.
 
     heap_page_items
     ---------------
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;
 
diff --git a/contrib/pageinspect/rawpage.c b/contrib/pageinspect/rawpage.c
index 4aba08e7800..80632be9fb5 100644
--- a/contrib/pageinspect/rawpage.c
+++ b/contrib/pageinspect/rawpage.c
@@ -8,7 +8,7 @@
  * Copyright (c) 2007, PostgreSQL Global Development Group
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/contrib/pageinspect/rawpage.c,v 1.1 2007/05/17 19:11:24 momjian Exp $
+ *	  $PostgreSQL: pgsql/contrib/pageinspect/rawpage.c,v 1.2 2007/09/21 21:25:42 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -110,8 +110,8 @@ page_header(PG_FUNCTION_ARGS)
 
 	Datum		result;
 	HeapTuple	tuple;
-	Datum		values[8];
-	bool		nulls[8];
+	Datum		values[9];
+	bool		nulls[9];
 
 	PageHeader	page;
 	XLogRecPtr	lsn;
@@ -152,6 +152,7 @@ page_header(PG_FUNCTION_ARGS)
 	values[5] = UInt16GetDatum(page->pd_special);
 	values[6] = UInt16GetDatum(PageGetPageSize(page));
 	values[7] = UInt16GetDatum(PageGetPageLayoutVersion(page));
+	values[8] = TransactionIdGetDatum(page->pd_prune_xid);
 
     /* Build and return the tuple. */