Be more careful about GucSource for internally-driven GUC settings.

The original advice for hard-wired SetConfigOption calls was to use
PGC_S_OVERRIDE, particularly for PGC_INTERNAL GUCs.  However,
that's really overkill for PGC_INTERNAL GUCs, since there is no
possibility that we need to override a user-provided setting.
Instead use PGC_S_DYNAMIC_DEFAULT in most places, so that the
value will appear with source = 'default' in pg_settings and thereby
not be shown by psql's new \dconfig command.  The one exception is
that when changing in_hot_standby in a hot-standby session, we still
use PGC_S_OVERRIDE, because people felt that seeing that in \dconfig
would be a good thing.

Similarly use PGC_S_DYNAMIC_DEFAULT for the auto-tune value of
wal_buffers (if possible, that is if wal_buffers wasn't explicitly
set to -1), and for the typical 2MB value of max_stack_depth.

In combination these changes remove four not-very-interesting
entries from the typical output of \dconfig, all of which people
fingered as "why is that showing up?" in the discussion thread.

Discussion: https://postgr.es/m/3118455.1649267333@sss.pgh.pa.us

src/backend/access/transam/xlog.c

@@ -4167,7 +4167,7 @@ ReadControlFile(void)
 
 	snprintf(wal_segsz_str, sizeof(wal_segsz_str), "%d", wal_segment_size);
 	SetConfigOption("wal_segment_size", wal_segsz_str, PGC_INTERNAL,
-					PGC_S_OVERRIDE);
+					PGC_S_DYNAMIC_DEFAULT);
 
 	/* check and update variables dependent on wal_segment_size */
 	if (ConvertToXSegs(min_wal_size_mb, wal_segment_size) < 2)
@@ -4186,7 +4186,7 @@ ReadControlFile(void)
 
 	/* Make the initdb settings visible as GUC variables, too */
 	SetConfigOption("data_checksums", DataChecksumsEnabled() ? "yes" : "no",
-					PGC_INTERNAL, PGC_S_OVERRIDE);
+					PGC_INTERNAL, PGC_S_DYNAMIC_DEFAULT);
 }
 
 /*
@@ -4343,13 +4343,22 @@ XLOGShmemSize(void)
 	 * This isn't an amazingly clean place to do this, but we must wait till
 	 * NBuffers has received its final value, and must do it before using the
 	 * value of XLOGbuffers to do anything important.
+	 *
+	 * We prefer to report this value's source as PGC_S_DYNAMIC_DEFAULT.
+	 * However, if the DBA explicitly set wal_buffers = -1 in the config file,
+	 * then PGC_S_DYNAMIC_DEFAULT will fail to override that and we must force
+	 * the matter with PGC_S_OVERRIDE.
 	 */
 	if (XLOGbuffers == -1)
 	{
 		char		buf[32];
 
 		snprintf(buf, sizeof(buf), "%d", XLOGChooseNumBuffers());
-		SetConfigOption("wal_buffers", buf, PGC_POSTMASTER, PGC_S_OVERRIDE);
+		SetConfigOption("wal_buffers", buf, PGC_POSTMASTER,
+						PGC_S_DYNAMIC_DEFAULT);
+		if (XLOGbuffers == -1)	/* failed to apply it? */
+			SetConfigOption("wal_buffers", buf, PGC_POSTMASTER,
+							PGC_S_OVERRIDE);
 	}
 	Assert(XLOGbuffers > 0);
 

src/backend/bootstrap/bootstrap.c

@@ -262,7 +262,7 @@ BootstrapModeMain(int argc, char *argv[], bool check_only)
 								(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
 								 errmsg("-X requires a power of two value between 1 MB and 1 GB")));
 					SetConfigOption("wal_segment_size", optarg, PGC_INTERNAL,
-									PGC_S_OVERRIDE);
+									PGC_S_DYNAMIC_DEFAULT);
 				}
 				break;
 			case 'c':

src/backend/postmaster/postmaster.c

@@ -921,7 +921,7 @@ PostmasterMain(int argc, char *argv[])
 		 * useful to show, even if one would only expect at least PANIC.  LOG
 		 * entries are hidden.
 		 */
-		SetConfigOption("log_min_messages", "FATAL", PGC_INTERNAL,
+		SetConfigOption("log_min_messages", "FATAL", PGC_SUSET,
 						PGC_S_OVERRIDE);
 	}
 

src/backend/storage/ipc/ipci.c

@@ -334,7 +334,8 @@ InitializeShmemGUCs(void)
 	size_b = CalculateShmemSize(NULL);
 	size_mb = add_size(size_b, (1024 * 1024) - 1) / (1024 * 1024);
 	sprintf(buf, "%zu", size_mb);
-	SetConfigOption("shared_memory_size", buf, PGC_INTERNAL, PGC_S_OVERRIDE);
+	SetConfigOption("shared_memory_size", buf,
+					PGC_INTERNAL, PGC_S_DYNAMIC_DEFAULT);
 
 	/*
 	 * Calculate the number of huge pages required.
@@ -346,6 +347,7 @@ InitializeShmemGUCs(void)
 
 		hp_required = add_size(size_b / hp_size, 1);
 		sprintf(buf, "%zu", hp_required);
-		SetConfigOption("shared_memory_size_in_huge_pages", buf, PGC_INTERNAL, PGC_S_OVERRIDE);
+		SetConfigOption("shared_memory_size_in_huge_pages", buf,
+						PGC_INTERNAL, PGC_S_DYNAMIC_DEFAULT);
 	}
 }

src/backend/utils/init/miscinit.c

@@ -787,7 +787,7 @@ InitializeSessionUserId(const char *rolename, Oid roleid)
 					PGC_BACKEND, PGC_S_OVERRIDE);
 	SetConfigOption("is_superuser",
 					AuthenticatedUserIsSuperuser ? "on" : "off",
-					PGC_INTERNAL, PGC_S_OVERRIDE);
+					PGC_INTERNAL, PGC_S_DYNAMIC_DEFAULT);
 
 	ReleaseSysCache(roleTup);
 }
@@ -844,7 +844,7 @@ SetSessionAuthorization(Oid userid, bool is_superuser)
 
 	SetConfigOption("is_superuser",
 					is_superuser ? "on" : "off",
-					PGC_INTERNAL, PGC_S_OVERRIDE);
+					PGC_INTERNAL, PGC_S_DYNAMIC_DEFAULT);
 }
 
 /*
@@ -901,7 +901,7 @@ SetCurrentRoleId(Oid roleid, bool is_superuser)
 
 	SetConfigOption("is_superuser",
 					is_superuser ? "on" : "off",
-					PGC_INTERNAL, PGC_S_OVERRIDE);
+					PGC_INTERNAL, PGC_S_DYNAMIC_DEFAULT);
 }
 
 

src/backend/utils/init/postinit.c

@@ -391,7 +391,7 @@ CheckMyDatabase(const char *name, bool am_superuser, bool override_allow_connect
 	SetDatabaseEncoding(dbform->encoding);
 	/* Record it as a GUC internal option, too */
 	SetConfigOption("server_encoding", GetDatabaseEncodingName(),
-					PGC_INTERNAL, PGC_S_OVERRIDE);
+					PGC_INTERNAL, PGC_S_DYNAMIC_DEFAULT);
 	/* If we have no other source of client_encoding, use server encoding */
 	SetConfigOption("client_encoding", GetDatabaseEncodingName(),
 					PGC_BACKEND, PGC_S_DYNAMIC_DEFAULT);
@@ -470,8 +470,8 @@ CheckMyDatabase(const char *name, bool am_superuser, bool override_allow_connect
 	}
 
 	/* Make the locale settings visible as GUC variables, too */
-	SetConfigOption("lc_collate", collate, PGC_INTERNAL, PGC_S_OVERRIDE);
-	SetConfigOption("lc_ctype", ctype, PGC_INTERNAL, PGC_S_OVERRIDE);
+	SetConfigOption("lc_collate", collate, PGC_INTERNAL, PGC_S_DYNAMIC_DEFAULT);
+	SetConfigOption("lc_ctype", ctype, PGC_INTERNAL, PGC_S_DYNAMIC_DEFAULT);
 
 	check_strxfrm_bug();
 

src/backend/utils/misc/guc-file.l

@@ -401,9 +401,8 @@ ProcessConfigFileInternal(GucContext context, bool applySettings, int elevel)
 	 * be run only after initialization is complete.
 	 *
 	 * XXX this is an unmaintainable crock, because we have to know how to set
-	 * (or at least what to call to set) every variable that could potentially
-	 * have PGC_S_DYNAMIC_DEFAULT or PGC_S_ENV_VAR source. However, there's no
-	 * time to redesign it for 9.1.
+	 * (or at least what to call to set) every non-PGC_INTERNAL variable that
+	 * could potentially have PGC_S_DYNAMIC_DEFAULT or PGC_S_ENV_VAR source.
 	 */
 	if (context == PGC_SIGHUP && applySettings)
 	{

src/backend/utils/misc/guc.c

@@ -5939,6 +5939,8 @@ InitializeGUCOptionsFromEnvironment(void)
 	 * rlimit isn't exactly an "environment variable", but it behaves about
 	 * the same.  If we can identify the platform stack depth rlimit, increase
 	 * default stack depth setting up to whatever is safe (but at most 2MB).
+	 * Report the value's source as PGC_S_DYNAMIC_DEFAULT if it's 2MB, or as
+	 * PGC_S_ENV_VAR if it's reflecting the rlimit limit.
 	 */
 	stack_rlimit = get_stack_depth_rlimit();
 	if (stack_rlimit > 0)
@@ -5947,12 +5949,19 @@ InitializeGUCOptionsFromEnvironment(void)
 
 		if (new_limit > 100)
 		{
+			GucSource	source;
 			char		limbuf[16];
 
-			new_limit = Min(new_limit, 2048);
-			sprintf(limbuf, "%ld", new_limit);
+			if (new_limit < 2048)
+				source = PGC_S_ENV_VAR;
+			else
+			{
+				new_limit = 2048;
+				source = PGC_S_DYNAMIC_DEFAULT;
+			}
+			snprintf(limbuf, sizeof(limbuf), "%ld", new_limit);
 			SetConfigOption("max_stack_depth", limbuf,
-							PGC_POSTMASTER, PGC_S_ENV_VAR);
+							PGC_POSTMASTER, source);
 		}
 	}
 }
@@ -6776,12 +6785,16 @@ BeginReportingGUCOptions(void)
 	reporting_enabled = true;
 
 	/*
-	 * Hack for in_hot_standby: initialize with the value we're about to send.
+	 * Hack for in_hot_standby: set the GUC value true if appropriate.  This
+	 * is kind of an ugly place to do it, but there's few better options.
+	 *
 	 * (This could be out of date by the time we actually send it, in which
 	 * case the next ReportChangedGUCOptions call will send a duplicate
 	 * report.)
 	 */
-	in_hot_standby = RecoveryInProgress();
+	if (RecoveryInProgress())
+		SetConfigOption("in_hot_standby", "true",
+						PGC_INTERNAL, PGC_S_OVERRIDE);
 
 	/* Transmit initial values of interesting variables */
 	for (i = 0; i < num_guc_variables; i++)
@@ -6822,15 +6835,8 @@ ReportChangedGUCOptions(void)
 	 * transition from false to true.
 	 */
 	if (in_hot_standby && !RecoveryInProgress())
-	{
-		struct config_generic *record;
-
-		record = find_option("in_hot_standby", false, false, ERROR);
-		Assert(record != NULL);
-		record->status |= GUC_NEEDS_REPORT;
-		report_needed = true;
-		in_hot_standby = false;
-	}
+		SetConfigOption("in_hot_standby", "false",
+						PGC_INTERNAL, PGC_S_OVERRIDE);
 
 	/* Quick exit if no values have been changed */
 	if (!report_needed)

src/include/utils/guc.h

@@ -83,8 +83,7 @@ typedef enum
  * override the postmaster command line.)  Tracking the source allows us
  * to process sources in any convenient order without affecting results.
  * Sources <= PGC_S_OVERRIDE will set the default used by RESET, as well
- * as the current value.  Note that source == PGC_S_OVERRIDE should be
- * used when setting a PGC_INTERNAL option.
+ * as the current value.
  *
  * PGC_S_INTERACTIVE isn't actually a source value, but is the
  * dividing line between "interactive" and "non-interactive" sources for
@@ -99,6 +98,11 @@ typedef enum
  * shouldn't throw hard errors in this case, at most NOTICEs, since the
  * objects might exist by the time the setting is used for real.
  *
+ * When setting the value of a non-compile-time-constant PGC_INTERNAL option,
+ * source == PGC_S_DYNAMIC_DEFAULT should typically be used so that the value
+ * will show as "default" in pg_settings.  If there is a specific reason not
+ * to want that, use source == PGC_S_OVERRIDE.
+ *
  * NB: see GucSource_Names in guc.c if you change this.
  */
 typedef enum