Revise the API for GUC variable assign hooks.

The previous functions of assign hooks are now split between check hooks
and assign hooks, where the former can fail but the latter shouldn't.
Aside from being conceptually clearer, this approach exposes the
"canonicalized" form of the variable value to guc.c without having to do
an actual assignment.  And that lets us fix the problem recently noted by
Bernd Helmle that the auto-tune patch for wal_buffers resulted in bogus
log messages about "parameter "wal_buffers" cannot be changed without
restarting the server".  There may be some speed advantage too, because
this design lets hook functions avoid re-parsing variable values when
restoring a previous state after a rollback (they can store a pre-parsed
representation of the value instead).  This patch also resolves a
longstanding annoyance about custom error messages from variable assign
hooks: they should modify, not appear separately from, guc.c's own message
about "invalid parameter value".

1 files changed, 17 insertions, 11 deletions

diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c
index 79c0f68966e..cc7945aeb66 100644
--- a/src/backend/tcop/postgres.c
+++ b/src/backend/tcop/postgres.c
@@ -2804,7 +2804,8 @@ RecoveryConflictInterrupt(ProcSignalReason reason)
 				break;
 
 			default:
-				elog(FATAL, "Unknown conflict mode");
+				elog(FATAL, "unrecognized conflict mode: %d",
+					 (int) reason);
 		}
 
 		Assert(RecoveryConflictPending && (QueryCancelPending || ProcDiePending));
@@ -3062,27 +3063,32 @@ check_stack_depth(void)
 #endif /* IA64 */
 }
 
-/* GUC assign hook for max_stack_depth */
+/* GUC check hook for max_stack_depth */
 bool
-assign_max_stack_depth(int newval, bool doit, GucSource source)
+check_max_stack_depth(int *newval, void **extra, GucSource source)
 {
-	long		newval_bytes = newval * 1024L;
+	long		newval_bytes = *newval * 1024L;
 	long		stack_rlimit = get_stack_depth_rlimit();
 
 	if (stack_rlimit > 0 && newval_bytes > stack_rlimit - STACK_DEPTH_SLOP)
 	{
-		ereport(GUC_complaint_elevel(source),
-				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
-				 errmsg("\"max_stack_depth\" must not exceed %ldkB",
-						(stack_rlimit - STACK_DEPTH_SLOP) / 1024L),
-				 errhint("Increase the platform's stack depth limit via \"ulimit -s\" or local equivalent.")));
+		GUC_check_errdetail("\"max_stack_depth\" must not exceed %ldkB.",
+							(stack_rlimit - STACK_DEPTH_SLOP) / 1024L);
+		GUC_check_errhint("Increase the platform's stack depth limit via \"ulimit -s\" or local equivalent.");
 		return false;
 	}
-	if (doit)
-		max_stack_depth_bytes = newval_bytes;
 	return true;
 }
 
+/* GUC assign hook for max_stack_depth */
+void
+assign_max_stack_depth(int newval, void *extra)
+{
+	long		newval_bytes = newval * 1024L;
+
+	max_stack_depth_bytes = newval_bytes;
+}
+
 
 /*
  * set_debug_options --- apply "-d N" command line option