Rewrite of planner statistics-gathering code. ANALYZE is now available as

a separate statement (though it can still be invoked as part of VACUUM, too).
pg_statistic redesigned to be more flexible about what statistics are
stored.  ANALYZE now collects a list of several of the most common values,
not just one, plus a histogram (not just the min and max values).  Random
sampling is used to make the process reasonably fast even on very large
tables.  The number of values and histogram bins collected is now
user-settable via an ALTER TABLE command.

There is more still to do; the new stats are not being used everywhere
they could be in the planner.  But the remaining changes for this project
should be localized, and the behavior is already better than before.

A not-very-related change is that sorting now makes use of btree comparison
routines if it can find one, rather than invoking '<' twice.

src/include/nodes/parsenodes.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2001, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $Id: parsenodes.h,v 1.126 2001/03/23 04:49:56 momjian Exp $
+ * $Id: parsenodes.h,v 1.127 2001/05/07 00:43:25 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -118,11 +118,12 @@ typedef struct AlterTableStmt
 	NodeTag		type;
 	char		subtype;		/*------------
 								 * 	A = add column
-								 *	T = alter column
+								 *	T = alter column default
+								 *	S = alter column statistics
 								 *	D = drop column
 								 *	C = add constraint
 								 *	X = drop constraint
-								 *	E = add toast table,
+								 *	E = create toast table
 								 *	U = change owner
 								 *------------
 								 */
@@ -690,16 +691,20 @@ typedef struct ClusterStmt
 } ClusterStmt;
 
 /* ----------------------
- *		Vacuum Statement
+ *		Vacuum and Analyze Statements
+ *
+ * Even though these are nominally two statements, it's convenient to use
+ * just one node type for both.
  * ----------------------
  */
 typedef struct VacuumStmt
 {
 	NodeTag		type;
-	bool		verbose;		/* print status info */
-	bool		analyze;		/* analyze data */
-	char	   *vacrel;			/* table to vacuum */
-	List	   *va_spec;		/* columns to analyse */
+	bool		vacuum;			/* do VACUUM step */
+	bool		analyze;		/* do ANALYZE step */
+	bool		verbose;		/* print progress info */
+	char	   *vacrel;			/* name of single table to process, or NULL */
+	List	   *va_cols;		/* list of column names, or NIL for all */
 } VacuumStmt;
 
 /* ----------------------