sql: add default_value and is_overridden to cluster settings

Fixes https://cockroachlabs.atlassian.net/browse/CRDB-28519

Previously, there was no easy way to see default values for
cluster settings. This commit add the column for `default_value`
and `origin` to `crdb_internal.cluster_settings` and
the `show cluster settings` command.

Release note (sql change): Add columns `default_value` and
`origin` (default, override, external-override) to the
`show cluster settings` command.

pkg/ccl/logictestccl/testdata/logic_test/crdb_internal_tenant

@@ -224,10 +224,10 @@ SELECT * FROM crdb_internal.session_trace WHERE span_idx < 0
 ----
 span_idx  message_idx  timestamp  duration  operation  loc  tag  message age
 
-query TTTBT colnames
+query TTTBTTT colnames
 SELECT * FROM crdb_internal.cluster_settings WHERE variable = ''
 ----
-variable  value  type  public  description
+variable  value  type  public  description default_value origin
 
 query TI colnames
 SELECT * FROM crdb_internal.feature_usage WHERE feature_name = ''

pkg/server/settings_test.go

@@ -276,7 +276,7 @@ func TestSettingsShowAll(t *testing.T) {
 	if len(rows) < 2 {
 		t.Fatalf("show all returned too few rows (%d)", len(rows))
 	}
-	const expColumns = 5
+	const expColumns = 7
 	if len(rows[0]) != expColumns {
 		t.Fatalf("show all must return %d columns, found %d", expColumns, len(rows[0]))
 	}

pkg/settings/setting.go

@@ -159,3 +159,7 @@ const (
 	// via a host-cluster override for this or all tenant(s).
 	OriginExternallySet
 )
+
+func (v ValueOrigin) String() string {
+	return [...]string{"default", "override", "external-override"}[v]
+}

pkg/sql/crdb_internal.go

@@ -2054,7 +2054,9 @@ CREATE TABLE crdb_internal.cluster_settings (
   value         STRING NOT NULL,
   type          STRING NOT NULL,
   public        BOOL NOT NULL, -- whether the setting is documented, which implies the user can expect support.
-  description   STRING NOT NULL
+  description   STRING NOT NULL,
+  default_value STRING NOT NULL,
+  origin        STRING NOT NULL -- the origin of the value: 'default' , 'override' or 'external-override'
 )`,
 	populate: func(ctx context.Context, p *planner, _ catalog.DatabaseDescriptor, addRow func(...tree.Datum) error) error {
 		hasSqlModify, err := p.HasPrivilege(ctx, syntheticprivilege.GlobalPrivilegeObject, privilege.MODIFYSQLCLUSTERSETTING, p.User())
@@ -2093,12 +2095,19 @@ CREATE TABLE crdb_internal.cluster_settings (
 			strVal := setting.String(&p.ExecCfg().Settings.SV)
 			isPublic := setting.Visibility() == settings.Public
 			desc := setting.Description()
+			defaultVal, err := setting.DecodeToString(setting.EncodedDefault())
+			if err != nil {
+				return err
+			}
+			origin := setting.ValueOrigin(ctx, &p.ExecCfg().Settings.SV).String()
 			if err := addRow(
 				tree.NewDString(k),
 				tree.NewDString(strVal),
 				tree.NewDString(setting.Typ()),
 				tree.MakeDBool(tree.DBool(isPublic)),
 				tree.NewDString(desc),
+				tree.NewDString(defaultVal),
+				tree.NewDString(origin),
 			); err != nil {
 				return err
 			}

pkg/sql/delegate/show_all_cluster_settings.go

@@ -77,12 +77,12 @@ func (d *delegator) delegateShowClusterSettingList(
 
 	if stmt.All {
 		return d.parse(
-			`SELECT variable, value, type AS setting_type, public, description
+			`SELECT variable, value, type AS setting_type, public, description, default_value, origin
        FROM   crdb_internal.cluster_settings`,
 		)
 	}
 	return d.parse(
-		`SELECT variable, value, type AS setting_type, description
+		`SELECT variable, value, type AS setting_type, description, default_value, origin
      FROM   crdb_internal.cluster_settings
      WHERE  public IS TRUE`,
 	)

pkg/sql/logictest/testdata/logic_test/cluster_settings

@@ -78,6 +78,21 @@ WHERE variable IN ('sql.defaults.default_int_size')
 ----
 sql.defaults.default_int_size  4
 
+query TTTT
+SELECT variable, value, default_value, origin FROM [SHOW ALL CLUSTER SETTINGS]
+WHERE variable IN ('sql.index_recommendation.drop_unused_duration')
+----
+sql.index_recommendation.drop_unused_duration  168h0m0s 168h0m0s default
+
+statement ok
+SET CLUSTER SETTING sql.index_recommendation.drop_unused_duration = '10s'
+
+query TTTT
+SELECT variable, value, default_value, origin FROM [SHOW ALL CLUSTER SETTINGS]
+WHERE variable IN ('sql.index_recommendation.drop_unused_duration')
+----
+sql.index_recommendation.drop_unused_duration  10s 168h0m0s override
+
 user root
 
 statement ok

pkg/sql/logictest/testdata/logic_test/crdb_internal

@@ -355,10 +355,10 @@ SELECT * FROM crdb_internal.session_trace WHERE span_idx < 0
 ----
 span_idx  message_idx  timestamp  duration  operation  loc  tag  message age
 
-query TTTBT colnames
+query TTTBTTT colnames
 SELECT * FROM crdb_internal.cluster_settings WHERE variable = ''
 ----
-variable  value  type  public  description
+variable  value  type  public  description  default_value  origin
 
 query TI colnames
 SELECT * FROM crdb_internal.feature_usage WHERE feature_name = ''

pkg/sql/logictest/testdata/logic_test/show_source

@@ -180,23 +180,23 @@ SELECT * FROM [SHOW CLUSTER SETTING sql.defaults.distsql]
 sql.defaults.distsql
 off
 
-query TTTBT colnames
+query TTTBTTT colnames
 SELECT * FROM [SHOW ALL CLUSTER SETTINGS] WHERE variable LIKE '%organization'
 ----
-variable              value  setting_type  public  description
-cluster.organization  ·      s             true    organization name
+variable              value  setting_type  public  description        default_value  origin
+cluster.organization  ·      s             true    organization name  ·              default
 
-query TTTT colnames
+query TTTTTT colnames
 SELECT * FROM [SHOW CLUSTER SETTINGS] WHERE variable LIKE '%organization'
 ----
-variable              value  setting_type  description
-cluster.organization  ·      s             organization name
+variable              value  setting_type  description        default_value  origin
+cluster.organization  ·      s             organization name  ·              default
 
-query TTTT colnames
+query TTTTTT colnames
 SELECT * FROM [SHOW PUBLIC CLUSTER SETTINGS] WHERE variable LIKE '%organization'
 ----
-variable              value  setting_type  description
-cluster.organization  ·      s             organization name
+variable              value  setting_type  description        default_value  origin
+cluster.organization  ·      s             organization name  ·              default
 
 query T colnames
 SELECT * FROM [SHOW SESSION_USER]