Improve vacuum code to track minimum Xids per table instead of per database.

To this end, add a couple of columns to pg_class, relminxid and relvacuumxid,
based on which we calculate the pg_database columns after each vacuum.

We now force all databases to be vacuumed, even template ones.  A backend
noticing too old a database (meaning pg_database.datminxid is in danger of
falling behind Xid wraparound) will signal the postmaster, which in turn will
start an autovacuum iteration to process the offending database.  In principle
this is only there to cope with frozen (non-connectable) databases without
forcing users to set them to connectable, but it could force regular user
database to go through a database-wide vacuum at any time.  Maybe we should
warn users about this somehow.  Of course the real solution will be to use
autovacuum all the time ;-)

There are some additional improvements we could have in this area: for example
the vacuum code could be smarter about not updating pg_database for each table
when called by autovacuum, and do it only once the whole autovacuum iteration
is done.

I updated the system catalogs documentation, but I didn't modify the
maintenance section.  Also having some regression tests for this would be nice
but it's not really a very straightforward thing to do.

Catalog version bumped due to system catalog changes.

1 files changed, 14 insertions, 9 deletions

diff --git a/src/include/catalog/pg_class.h b/src/include/catalog/pg_class.h
index 6d303b1cd6..931875a4c5 100644
--- a/src/include/catalog/pg_class.h
+++ b/src/include/catalog/pg_class.h
@@ -8,7 +8,7 @@
  * Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/catalog/pg_class.h,v 1.94 2006/07/03 22:45:40 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/catalog/pg_class.h,v 1.95 2006/07/10 16:20:51 alvherre Exp $
  *
  * NOTES
  *	  the genbki.sh script reads this file and generates .bki
@@ -65,6 +65,8 @@ CATALOG(pg_class,1259) BKI_BOOTSTRAP
 	bool		relhaspkey;		/* has PRIMARY KEY index */
 	bool		relhasrules;	/* has associated rules */
 	bool		relhassubclass; /* has derived classes */
+	TransactionId relminxid;	/* minimum Xid present in table */
+	TransactionId relvacuumxid;	/* Xid used as last vacuum OldestXmin */
 
 	/*
 	 * VARIABLE LENGTH FIELDS start here.  These fields may be NULL, too.
@@ -78,7 +80,7 @@ CATALOG(pg_class,1259) BKI_BOOTSTRAP
 
 /* Size of fixed part of pg_class tuples, not counting var-length fields */
 #define CLASS_TUPLE_SIZE \
-	 (offsetof(FormData_pg_class,relhassubclass) + sizeof(bool))
+	 (offsetof(FormData_pg_class,relvacuumxid) + sizeof(TransactionId))
 
 /* ----------------
  *		Form_pg_class corresponds to a pointer to a tuple with
@@ -92,7 +94,7 @@ typedef FormData_pg_class *Form_pg_class;
  * ----------------
  */
 
-#define Natts_pg_class					26
+#define Natts_pg_class					28
 #define Anum_pg_class_relname			1
 #define Anum_pg_class_relnamespace		2
 #define Anum_pg_class_reltype			3
@@ -117,8 +119,10 @@ typedef FormData_pg_class *Form_pg_class;
 #define Anum_pg_class_relhaspkey		22
 #define Anum_pg_class_relhasrules		23
 #define Anum_pg_class_relhassubclass	24
-#define Anum_pg_class_relacl			25
-#define Anum_pg_class_reloptions		26
+#define Anum_pg_class_relminxid			25
+#define Anum_pg_class_relvacuumxid		26
+#define Anum_pg_class_relacl			27
+#define Anum_pg_class_reloptions		28
 
 /* ----------------
  *		initial contents of pg_class
@@ -128,13 +132,14 @@ typedef FormData_pg_class *Form_pg_class;
  * ----------------
  */
 
-DATA(insert OID = 1247 (  pg_type		PGNSP 71 PGUID 0 1247 0 0 0 0 0 f f r 23 0 0 0 0 0 t f f f _null_ _null_ ));
+/* Note: the "3" here stands for FirstNormalTransactionId */
+DATA(insert OID = 1247 (  pg_type		PGNSP 71 PGUID 0 1247 0 0 0 0 0 f f r 23 0 0 0 0 0 t f f f 3 3 _null_ _null_ ));
 DESCR("");
-DATA(insert OID = 1249 (  pg_attribute	PGNSP 75 PGUID 0 1249 0 0 0 0 0 f f r 17 0 0 0 0 0 f f f f _null_ _null_ ));
+DATA(insert OID = 1249 (  pg_attribute	PGNSP 75 PGUID 0 1249 0 0 0 0 0 f f r 17 0 0 0 0 0 f f f f 3 3 _null_ _null_ ));
 DESCR("");
-DATA(insert OID = 1255 (  pg_proc		PGNSP 81 PGUID 0 1255 0 0 0 0 0 f f r 18 0 0 0 0 0 t f f f _null_ _null_ ));
+DATA(insert OID = 1255 (  pg_proc		PGNSP 81 PGUID 0 1255 0 0 0 0 0 f f r 18 0 0 0 0 0 t f f f 3 3 _null_ _null_ ));
 DESCR("");
-DATA(insert OID = 1259 (  pg_class		PGNSP 83 PGUID 0 1259 0 0 0 0 0 f f r 26 0 0 0 0 0 t f f f _null_ _null_ ));
+DATA(insert OID = 1259 (  pg_class		PGNSP 83 PGUID 0 1259 0 0 0 0 0 f f r 28 0 0 0 0 0 t f f f 3 3 _null_ _null_ ));
 DESCR("");
 
 #define		  RELKIND_INDEX			  'i'		/* secondary index */