Create new errcode for recovery conflict caused by db drop on master.

Previously reported as ERRCODE_ADMIN_SHUTDOWN, this case is now
reported as ERRCODE_DATABASE_DROPPED. No message text change.
Unlikely to happen on most servers, so low impact change to allow
session poolers to correctly handle this situation.

Tatsuo Ishii and Simon Riggs

doc/src/sgml/errcodes.sgml

@@ -1369,6 +1369,12 @@
 <entry>cannot_connect_now</entry>
 </row>
 
+<row>
+<entry><literal>57P04</literal></entry>
+<entry>DATABASE DROPPED</entry>
+<entry>database_dropped</entry>
+</row>
+
 
 <row>
 <entry spanname="span13"><emphasis role="bold">Class 58 &mdash; System Error (errors external to <productname>PostgreSQL</> itself)</></entry>

src/backend/tcop/postgres.c

@@ -2908,7 +2908,7 @@ ProcessInterrupts(void)
 					 errdetail_recovery_conflict()));
 		else if (RecoveryConflictPending)
 			ereport(FATAL,
-					(errcode(ERRCODE_ADMIN_SHUTDOWN),
+					(errcode(ERRCODE_DATABASE_DROPPED),
 			  errmsg("terminating connection due to conflict with recovery"),
 					 errdetail_recovery_conflict()));
 		else

src/include/utils/errcodes.h

@@ -332,6 +332,7 @@
 #define ERRCODE_ADMIN_SHUTDOWN				MAKE_SQLSTATE('5','7', 'P','0','1')
 #define ERRCODE_CRASH_SHUTDOWN				MAKE_SQLSTATE('5','7', 'P','0','2')
 #define ERRCODE_CANNOT_CONNECT_NOW			MAKE_SQLSTATE('5','7', 'P','0','3')
+#define ERRCODE_DATABASE_DROPPED			MAKE_SQLSTATE('5','7', 'P','0','4')
 
 /* Class 58 - System Error (class borrowed from DB2) */
 /* (we define this as errors external to PostgreSQL itself) */

src/pl/plpgsql/src/plerrcodes.h

@@ -735,6 +735,10 @@
 	"cannot_connect_now", ERRCODE_CANNOT_CONNECT_NOW
 },
 
+{
+	"database_dropped", ERRCODE_DATABASE_DROPPED
+},
+
 {
 	"io_error", ERRCODE_IO_ERROR
 },