workload: treat rename destination conflicts as potential errors

Rename operations (e.g., sequences, tables) check for name conflicts at
snapshot time but execute later, allowing concurrent transactions to change
the destination state. This can cause expected errors (e.g., DuplicateRelation)
to not occur, leading to false workload failures.

The workload now treats such cases as potential errors instead of hard
failures.

Example:
```
TX1: Checks seq_w18_32 exists → TRUE
TX1: Expects error on renaming to seq_w18_32
TX2: Renames seq_w18_32 away → commits
TX1: Rename unexpectedly succeeds
- workload fails: error was expected but not raised
```

Closes #160465
Release note: none
Epic: none

Author: spilchen

pkg/workload/schemachange/operation_generator.go

@@ -2251,21 +2251,21 @@ func (og *operationGenerator) renameColumn(ctx context.Context, tx pgx.Tx) (*opS
 	if err != nil {
 		return nil, err
 	}
-	destColumnExists, err := og.columnExistsOnTable(ctx, tx, tableName, destColumnName)
-	if err != nil {
-		return nil, err
-	}
 
 	stmt := makeOpStmt(OpStmtDDL)
 	stmt.expectedExecErrors.addAll(codesWithConditions{
 		{pgcode.UndefinedColumn, !srcColumnExists},
-		{pgcode.DuplicateColumn, destColumnExists && srcColumnName != destColumnName},
 	})
-	// The column may be referenced in a view or trigger, which can lead to a
-	// dependency error. This is particularly hard to detect in cases where renaming
-	// a column that is part of a hash-sharded primary key triggers a cascading rename
-	// of the crdb_internal shard column, which might be used indirectly by other objects.
-	stmt.potentialExecErrors.add(pgcode.DependentObjectsStillExist)
+	stmt.potentialExecErrors.addAll(codesWithConditions{
+		// The column may be referenced in a view or trigger, which can lead to a
+		// dependency error. This is particularly hard to detect in cases where renaming
+		// a column that is part of a hash-sharded primary key triggers a cascading rename
+		// of the crdb_internal shard column, which might be used indirectly by other objects.
+		{code: pgcode.DependentObjectsStillExist, condition: true},
+		// Duplicate name errors are potential because destination name conflicts
+		// can change after checking.
+		{code: pgcode.DuplicateColumn, condition: srcColumnName != destColumnName},
+	})
 
 	stmt.sql = fmt.Sprintf(`ALTER TABLE %s RENAME COLUMN %s TO %s`,
 		tableName.String(), srcColumnName.String(), destColumnName.String())
@@ -2307,15 +2307,15 @@ func (og *operationGenerator) renameIndex(ctx context.Context, tx pgx.Tx) (*opSt
 	if err != nil {
 		return nil, err
 	}
-	destIndexExists, err := og.indexExists(ctx, tx, tableName, destIndexName)
-	if err != nil {
-		return nil, err
-	}
 
 	stmt := makeOpStmt(OpStmtDDL)
 	stmt.expectedExecErrors.addAll(codesWithConditions{
 		{code: pgcode.UndefinedObject, condition: !srcIndexExists},
-		{code: pgcode.DuplicateRelation, condition: destIndexExists && srcIndexName != destIndexName},
+	})
+	// Duplicate name errors are potential because destination name conflicts can
+	// change after checking.
+	stmt.potentialExecErrors.addAll(codesWithConditions{
+		{code: pgcode.DuplicateRelation, condition: srcIndexName != destIndexName},
 	})
 
 	stmt.sql = fmt.Sprintf(`ALTER INDEX %s@"%s" RENAME TO "%s"`,
@@ -2350,19 +2350,18 @@ func (og *operationGenerator) renameSequence(ctx context.Context, tx pgx.Tx) (*o
 		return nil, err
 	}
 
-	destSequenceExists, err := og.sequenceExists(ctx, tx, destSequenceName)
-	if err != nil {
-		return nil, err
-	}
-
 	srcEqualsDest := srcSequenceName.String() == destSequenceName.String()
 	stmt := makeOpStmt(OpStmtDDL)
 	stmt.expectedExecErrors.addAll(codesWithConditions{
 		{code: pgcode.UndefinedTable, condition: !srcSequenceExists},
 		{code: pgcode.UndefinedSchema, condition: !destSchemaExists},
-		{code: pgcode.DuplicateRelation, condition: !srcEqualsDest && destSequenceExists},
 		{code: pgcode.InvalidName, condition: srcSequenceName.Schema() != destSequenceName.Schema()},
 	})
+	// Duplicate name errors are potential because destination name conflicts can
+	// change after checking.
+	stmt.potentialExecErrors.addAll(codesWithConditions{
+		{code: pgcode.DuplicateRelation, condition: !srcEqualsDest},
+	})
 
 	stmt.sql = fmt.Sprintf(`ALTER SEQUENCE %s RENAME TO %s`, srcSequenceName, destSequenceName)
 	return stmt, nil
@@ -2400,11 +2399,6 @@ func (og *operationGenerator) renameTable(ctx context.Context, tx pgx.Tx) (*opSt
 		return nil, err
 	}
 
-	destTableExists, err := og.tableExists(ctx, tx, destTableName)
-	if err != nil {
-		return nil, err
-	}
-
 	srcTableHasDependencies, err := og.tableHasDependencies(ctx, tx, srcTableName, false, /* includeFKs */
 		false /* skipSelfRef */)
 	if err != nil {
@@ -2416,10 +2410,14 @@ func (og *operationGenerator) renameTable(ctx context.Context, tx pgx.Tx) (*opSt
 	stmt.expectedExecErrors.addAll(codesWithConditions{
 		{code: pgcode.UndefinedTable, condition: !srcTableExists},
 		{code: pgcode.UndefinedSchema, condition: !destSchemaExists},
-		{code: pgcode.DuplicateRelation, condition: !srcEqualsDest && destTableExists},
 		{code: pgcode.DependentObjectsStillExist, condition: srcTableHasDependencies},
 		{code: pgcode.InvalidName, condition: srcTableName.Schema() != destTableName.Schema()},
 	})
+	// Duplicate name errors are potential because destination name conflicts can
+	// change after checking.
+	stmt.potentialExecErrors.addAll(codesWithConditions{
+		{code: pgcode.DuplicateRelation, condition: !srcEqualsDest},
+	})
 
 	stmt.sql = fmt.Sprintf(`ALTER TABLE %s RENAME TO %s`, srcTableName, destTableName)
 	return stmt, nil
@@ -2451,11 +2449,6 @@ func (og *operationGenerator) renameView(ctx context.Context, tx pgx.Tx) (*opStm
 		return nil, err
 	}
 
-	destViewExists, err := og.viewExists(ctx, tx, destViewName)
-	if err != nil {
-		return nil, err
-	}
-
 	srcTableHasDependencies, err := og.tableHasDependencies(ctx, tx, srcViewName, true, /* includeFKs */
 		false /* skipSelfRef */)
 	if err != nil {
@@ -2467,10 +2460,14 @@ func (og *operationGenerator) renameView(ctx context.Context, tx pgx.Tx) (*opStm
 	stmt.expectedExecErrors.addAll(codesWithConditions{
 		{code: pgcode.UndefinedTable, condition: !srcViewExists},
 		{code: pgcode.UndefinedSchema, condition: !destSchemaExists},
-		{code: pgcode.DuplicateRelation, condition: !srcEqualsDest && destViewExists},
 		{code: pgcode.DependentObjectsStillExist, condition: srcTableHasDependencies},
 		{code: pgcode.InvalidName, condition: srcViewName.Schema() != destViewName.Schema()},
 	})
+	// Duplicate name errors are potential because destination name conflicts can
+	// change after checking.
+	stmt.potentialExecErrors.addAll(codesWithConditions{
+		{code: pgcode.DuplicateRelation, condition: !srcEqualsDest},
+	})
 
 	stmt.sql = fmt.Sprintf(`ALTER VIEW %s RENAME TO %s`, srcViewName, destViewName)
 	return stmt, nil