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

1 files changed, 12 insertions, 3 deletions

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 71136b11a2a..8764084e215 100644
--- a/src/backend/access/transam/xlog.c
+++ b/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);