workload/schemachange: implement COMMENT ON

This commit adds support for attaching comments to various schema
elements in the RSW. Notably, commenting on databases has been omitted
as the workload operates within the scope of a given database.

Unfortunately, `COMMENT ON` will consistently trigger the bug reported
in #72820. Therefore it is disabled by default.

Epic: CRDB-19168
Informs: CRDB-3265
Informs: #72820
Release note: None

pkg/workload/schemachange/operation_generator.go

@@ -2687,6 +2687,40 @@ func (og *operationGenerator) survive(ctx context.Context, tx pgx.Tx) (*opStmt,
 	return stmt, nil
 }
 
+func (og *operationGenerator) commentOn(ctx context.Context, tx pgx.Tx) (*opStmt, error) {
+	q := With([]CTE{
+		{"descriptors", descJSONQuery},
+		{"tables", tableDescQuery},
+		{"columns", `SELECT schema_id::REGNAMESPACE::TEXT as schema_name, name AS table_name, jsonb_array_elements(descriptor->'table'->'columns') AS column FROM tables`},
+		{"indexes", `SELECT schema_id::REGNAMESPACE::TEXT as schema_name, name AS table_name, jsonb_array_elements(descriptor->'table'->'indexes') AS index FROM tables`},
+		{"constraints", `SELECT schema_id::REGNAMESPACE::TEXT as schema_name, name AS table_name, jsonb_array_elements(descriptor->'table'->'checks') AS constraint FROM tables`},
+	}, `
+	SELECT 'SCHEMA ' || quote_ident(schema_name) FROM [SHOW SCHEMAS] WHERE owner != 'node'
+		UNION ALL
+	SELECT 'TABLE ' || quote_ident(schema_name) || '.' || quote_ident(table_name) FROM [SHOW TABLES] WHERE type = 'table'
+		UNION ALL
+	SELECT 'COLUMN ' || quote_ident(schema_name) || '.' || quote_ident(table_name) || '.' || quote_ident("column"->>'name') FROM columns
+		UNION ALL
+	SELECT 'INDEX ' || quote_ident(schema_name) || '.' || quote_ident(table_name) || '@' || quote_ident("index"->>'name') FROM indexes
+		UNION ALL
+	SELECT 'CONSTRAINT ' || quote_ident("constraint"->>'name') || ' ON ' || quote_ident(schema_name) || '.' || quote_ident(table_name) FROM constraints
+	`)
+
+	commentables, err := Collect(ctx, og, tx, pgx.RowTo[string], q)
+	if err != nil {
+		return nil, err
+	}
+
+	picked, err := PickOne(og.params.rng, commentables)
+	if err != nil {
+		return nil, err
+	}
+
+	stmt := makeOpStmt(OpStmtDDL)
+	stmt.sql = fmt.Sprintf(`COMMENT ON %s IS 'comment from the RSW'`, picked)
+	return stmt, nil
+}
+
 func (og *operationGenerator) insertRow(ctx context.Context, tx pgx.Tx) (stmt *opStmt, err error) {
 	tableName, err := og.randTable(ctx, tx, og.pctExisting(true), "")
 	if err != nil {

pkg/workload/schemachange/optype.go

@@ -126,6 +126,10 @@ const (
 	createView     // CREATE VIEW <view> AS <def>
 	createFunction // CREATE FUNCTION <function> ...
 
+	// COMMENT ON ...
+
+	commentOn // COMMENT ON [SCHEMA | TABLE | INDEX | COLUMN | CONSTRAINT] IS <comment>
+
 	// DROP ...
 
 	dropFunction // DROP FUNCTION <function>
@@ -169,12 +173,7 @@ const (
 	// alterTypeRename
 	// alterTypeRenameValue
 	// alterTypeSetSchema
-	// commentOnColumn
-	// commentOnConstraint
 	// commentOnDatabase
-	// commentOnIndex
-	// commentOnSchema
-	// commentOnTable
 	// createDatabase
 	// createRole
 	// createStats
@@ -230,6 +229,7 @@ var opFuncs = []func(*operationGenerator, context.Context, pgx.Tx) (*opStmt, err
 	alterTableSetColumnDefault:        (*operationGenerator).setColumnDefault,
 	alterTableSetColumnNotNull:        (*operationGenerator).setColumnNotNull,
 	alterTypeDropValue:                (*operationGenerator).alterTypeDropValue,
+	commentOn:                         (*operationGenerator).commentOn,
 	createFunction:                    (*operationGenerator).createFunction,
 	createIndex:                       (*operationGenerator).createIndex,
 	createSchema:                      (*operationGenerator).createSchema,
@@ -257,46 +257,47 @@ var opWeights = []int{
 	validate:   2, // validate twice more often
 
 	// DDL Operations
-	alterTableAddColumn:               1,
-	alterTableDropConstraint:          0, // TODO(spaskob): unimplemented
-	alterTableAddConstraintForeignKey: 1, // Tentatively re-enabled, see #91195.
 	alterDatabaseAddRegion:            1,
 	alterDatabaseAddSuperRegion:       0, // Disabled and tracked with #111299
 	alterDatabaseDropSuperRegion:      0, // Disabled and tracked with #111299
 	alterDatabasePrimaryRegion:        0, // Disabled and tracked with #83831
 	alterDatabaseSurvivalGoal:         0, // Disabled and tracked with #83831
+	alterFunctionRename:               1,
+	alterFunctionSetSchema:            1,
+	alterTableAddColumn:               1,
+	alterTableAddConstraintForeignKey: 1, // Tentatively re-enabled, see #91195.
 	alterTableAddConstraintUnique:     0,
+	alterTableAlterColumnType:         0, // Disabled and tracked with #66662.
+	alterTableAlterPrimaryKey:         1,
+	alterTableDropColumn:              0,
+	alterTableDropColumnDefault:       1,
+	alterTableDropConstraint:          0, // TODO(spaskob): unimplemented
+	alterTableDropNotNull:             1,
+	alterTableDropStored:              1,
 	alterTableLocality:                1,
+	alterTableRenameColumn:            1,
+	alterTableSetColumnDefault:        1,
+	alterTableSetColumnNotNull:        1,
+	alterTypeDropValue:                0, // Disabled and tracked with #114844, #113859, and #115612.
+	commentOn:                         0,
+	createFunction:                    1,
 	createIndex:                       1,
+	createSchema:                      1,
 	createSequence:                    1,
 	createTable:                       1,
 	createTableAs:                     1,
-	createView:                        1,
 	createTypeEnum:                    1,
-	createSchema:                      1,
-	createFunction:                    1,
-	alterFunctionSetSchema:            1,
-	alterFunctionRename:               1,
-	alterTableDropColumn:              0,
-	alterTableDropColumnDefault:       1,
-	alterTableDropNotNull:             1,
-	alterTableDropStored:              1,
+	createView:                        1,
+	dropFunction:                      1,
 	dropIndex:                         1,
+	dropSchema:                        0, // TODO Make a tracking issue
 	dropSequence:                      1,
 	dropTable:                         1,
 	dropView:                          1,
-	alterTypeDropValue:                0, // Disabled and tracked with #114844, #113859, and #115612.
-	dropFunction:                      1,
-	dropSchema:                        0, // TODO Make a tracking issue
-	alterTableRenameColumn:            1,
 	renameIndex:                       1,
 	renameSequence:                    1,
 	renameTable:                       1,
 	renameView:                        1,
-	alterTableSetColumnDefault:        1,
-	alterTableSetColumnNotNull:        1,
-	alterTableAlterPrimaryKey:         1,
-	alterTableAlterColumnType:         0, // Disabled and tracked with #66662.
 }
 
 // This workload will maintain its own list of minimal supported versions for
@@ -311,9 +312,10 @@ var opDeclarativeVersion = map[opType]clusterversion.Key{
 	alterTableDropConstraint:          clusterversion.MinSupported,
 	alterTableDropNotNull:             clusterversion.MinSupported,
 	alterTypeDropValue:                clusterversion.MinSupported,
+	commentOn:                         clusterversion.MinSupported,
 	createIndex:                       clusterversion.MinSupported,
-	createSequence:                    clusterversion.MinSupported,
 	createSchema:                      clusterversion.V23_2,
+	createSequence:                    clusterversion.MinSupported,
 	dropIndex:                         clusterversion.MinSupported,
 	dropSchema:                        clusterversion.MinSupported,
 	dropSequence:                      clusterversion.MinSupported,