Keep track of the last active slot in the shared ProcState array, so

that search loops only have to scan that far and not through all maxBackends
entries.  This eliminates a performance penalty for setting maxBackends
much higher than the average number of active backends.  Also, eliminate
no-longer-used 'backend tag' concept.  Remove setting of environment
variables at backend start (except for CYR_RECODE), since none of them
are being examined by the backend any longer.

src/include/storage/sinvaladt.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2000, PostgreSQL, Inc
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $Id: sinvaladt.h,v 1.22 2000/06/15 03:33:00 momjian Exp $
+ * $Id: sinvaladt.h,v 1.23 2000/11/12 20:51:52 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -77,7 +77,6 @@ typedef struct ProcState
 	/* nextMsgNum is -1 in an inactive ProcState array entry. */
 	int			nextMsgNum;		/* next message number to read, or -1 */
 	bool		resetState;		/* true, if backend has to reset its state */
-	int			tag;			/* backend tag received from postmaster */
 	SHMEM_OFFSET procStruct;	/* location of backend's PROC struct */
 } ProcState;
 
@@ -90,6 +89,7 @@ typedef struct SISeg
 	 */
 	int			minMsgNum;		/* oldest message still needed */
 	int			maxMsgNum;		/* next message number to be assigned */
+	int			lastBackend;	/* index of last active procState entry, +1 */
 	int			maxBackends;	/* size of procState array */
 
 	/*