sql: disallow schema changes for READ COMMITTED transactions

Due to how descriptor leasing works, schema changes are not safe in
weaker isolation transactions. Until they are safe, we disallow them.

Release note: None

pkg/sql/logictest/testdata/logic_test/select_for_update_read_committed → pkg/sql/logictest/testdata/logic_test/read_committed

@@ -1,5 +1,7 @@
 # LogicTest: !local-mixed-22.2-23.1
 
+subtest select_for_update
+
 # SELECT FOR UPDATE is prohibited under weaker isolation levels until we improve
 # locking. See #57031, #75457, #100144.
 
@@ -88,22 +90,27 @@ SELECT aisle + 1 FROM s
 statement ok
 ROLLBACK
 
-statement ok
-SET SESSION CHARACTERISTICS AS TRANSACTION ISOLATION LEVEL READ COMMITTED
-
-# Creating a UDF using SELECT FOR UPDATE should succeed under read committed.
 statement ok
 CREATE FUNCTION wrangle (name STRING) RETURNS INT LANGUAGE SQL AS $$
   SELECT aisle FROM supermarket WHERE person = name FOR UPDATE
 $$
 
+statement ok
+SET SESSION CHARACTERISTICS AS TRANSACTION ISOLATION LEVEL READ COMMITTED
+
 # But calling that function should fail.
 query error pgcode 0A000 cannot execute SELECT FOR UPDATE statements under ReadCommitted isolation
 INSERT INTO supermarket (person, aisle) VALUES ('grandma', wrangle('matilda'))
 
+statement ok
+SET SESSION CHARACTERISTICS AS TRANSACTION ISOLATION LEVEL SERIALIZABLE
+
 statement ok
 DROP FUNCTION wrangle
 
+statement ok
+SET SESSION CHARACTERISTICS AS TRANSACTION ISOLATION LEVEL READ COMMITTED
+
 # Preparing a SELECT FOR UPDATE should succeed under read committed.
 statement ok
 PREPARE psa AS SELECT aisle FROM supermarket WHERE person = $1::STRING FOR UPDATE
@@ -138,5 +145,92 @@ SELECT aisle
   WHERE starts_with = 'm' AND ends_with = 'lda'
   FOR UPDATE
 
+subtest end
+
+subtest schema_changes
+
+# Schema changes are prohibited under weaker isolation levels.
+
+statement error transaction involving a schema change needs to be SERIALIZABLE
+ALTER TABLE supermarket ADD COLUMN age INT
+
+statement error transaction involving a schema change needs to be SERIALIZABLE
+CREATE TABLE foo(a INT)
+
+statement error transaction involving a schema change needs to be SERIALIZABLE
+DROP TABLE supermarket
+
+statement error transaction involving a schema change needs to be SERIALIZABLE
+CREATE USER foo
+
+statement error transaction involving a schema change needs to be SERIALIZABLE
+DROP USER testuser
+
+statement error transaction involving a schema change needs to be SERIALIZABLE
+GRANT admin TO testuser
+
+statement error transaction involving a schema change needs to be SERIALIZABLE
+GRANT SELECT ON supermarket TO testuser
+
+statement error transaction involving a schema change needs to be SERIALIZABLE
+GRANT USAGE ON SCHEMA public TO testuser
+
+statement error transaction involving a schema change needs to be SERIALIZABLE
+GRANT CONNECT ON DATABASE postgres TO testuser
+
+statement error transaction involving a schema change needs to be SERIALIZABLE
+CREATE INDEX foo ON supermarket(ends_with, starts_with)
+
+statement error transaction involving a schema change needs to be SERIALIZABLE
+CREATE FUNCTION f (x INT) RETURNS INT LANGUAGE SQL AS $$
+  SELECT x+1
+$$
+
+statement ok
+BEGIN TRANSACTION ISOLATION LEVEL SERIALIZABLE;
+CREATE FUNCTION f (x INT) RETURNS INT LANGUAGE SQL AS $$
+  SELECT x+1
+$$;
+COMMIT
+
+statement error transaction involving a schema change needs to be SERIALIZABLE
+ALTER FUNCTION f (x INT) RENAME TO g
+
+statement error transaction involving a schema change needs to be SERIALIZABLE
+GRANT EXECUTE ON FUNCTION f (x INT) TO testuser
+
+statement error transaction involving a schema change needs to be SERIALIZABLE
+CREATE TYPE typ AS ENUM('a', 'b')
+
+statement ok
+BEGIN TRANSACTION ISOLATION LEVEL SERIALIZABLE;
+CREATE TYPE typ AS ENUM('a', 'b');
+COMMIT
+
+statement error transaction involving a schema change needs to be SERIALIZABLE
+ALTER TYPE typ ADD VALUE 'c'
+
+statement error transaction involving a schema change needs to be SERIALIZABLE
+GRANT USAGE ON TYPE typ TO testuser
+
+statement error transaction involving a schema change needs to be SERIALIZABLE
+CREATE DATABASE foo
+
+statement error transaction involving a schema change needs to be SERIALIZABLE
+ALTER DATABASE postgres RENAME TO foo
+
+statement error transaction involving a schema change needs to be SERIALIZABLE
+CREATE SCHEMA s
+
+statement ok
+BEGIN TRANSACTION ISOLATION LEVEL SERIALIZABLE;
+CREATE SCHEMA s;
+COMMIT
+
+statement error transaction involving a schema change needs to be SERIALIZABLE
+ALTER SCHEMA s RENAME TO foo
+
+subtest end
+
 statement ok
 SET SESSION CHARACTERISTICS AS TRANSACTION ISOLATION LEVEL SERIALIZABLE

pkg/sql/opt/exec/execbuilder/relational.go

@@ -168,6 +168,11 @@ func (b *Builder) buildRelational(e memo.RelExpr) (execPlan, error) {
 	var err error
 
 	if opt.IsDDLOp(e) {
+		if b.evalCtx.Txn.IsoLevel().ToleratesWriteSkew() {
+			return execPlan{}, pgerror.Newf(
+				pgcode.FeatureNotSupported, "transaction involving a schema change needs to be SERIALIZABLE",
+			)
+		}
 		// Mark the statement as containing DDL for use
 		// in the SQL executor.
 		b.IsDDL = true

pkg/sql/sem/tree/stmt.go

@@ -554,7 +554,7 @@ func (*AlterSequence) StatementType() StatementType { return TypeDDL }
 func (*AlterSequence) StatementTag() string { return "ALTER SEQUENCE" }
 
 // StatementReturnType implements the Statement interface.
-func (*AlterRole) StatementReturnType() StatementReturnType { return Ack }
+func (*AlterRole) StatementReturnType() StatementReturnType { return DDL }
 
 // StatementType implements the Statement interface.
 func (*AlterRole) StatementType() StatementType { return TypeDCL }
@@ -565,7 +565,7 @@ func (*AlterRole) StatementTag() string { return "ALTER ROLE" }
 func (*AlterRole) hiddenFromShowQueries() {}
 
 // StatementReturnType implements the Statement interface.
-func (*AlterRoleSet) StatementReturnType() StatementReturnType { return Ack }
+func (*AlterRoleSet) StatementReturnType() StatementReturnType { return DDL }
 
 // StatementType implements the Statement interface.
 func (*AlterRoleSet) StatementType() StatementType { return TypeDCL }
@@ -932,7 +932,7 @@ func (*CreateType) StatementTag() string { return "CREATE TYPE" }
 func (*CreateType) modifiesSchema() bool { return true }
 
 // StatementReturnType implements the Statement interface.
-func (*CreateRole) StatementReturnType() StatementReturnType { return Ack }
+func (*CreateRole) StatementReturnType() StatementReturnType { return DDL }
 
 // StatementType implements the Statement interface.
 func (*CreateRole) StatementType() StatementType { return TypeDCL }
@@ -1063,7 +1063,7 @@ func (*DropSequence) StatementType() StatementType { return TypeDDL }
 func (*DropSequence) StatementTag() string { return "DROP SEQUENCE" }
 
 // StatementReturnType implements the Statement interface.
-func (*DropRole) StatementReturnType() StatementReturnType { return Ack }
+func (*DropRole) StatementReturnType() StatementReturnType { return DDL }
 
 // StatementType implements the Statement interface.
 func (*DropRole) StatementType() StatementType { return TypeDCL }

pkg/sql/table.go

@@ -106,7 +106,6 @@ func (p *planner) createNonDropDatabaseChangeJob(
 func (p *planner) createOrUpdateSchemaChangeJob(
 	ctx context.Context, tableDesc *tabledesc.Mutable, jobDesc string, mutationID descpb.MutationID,
 ) error {
-
 	// If there is a concurrent schema change using the declarative schema
 	// changer, then we must fail and wait for that schema change to conclude.
 	// The error here will be dealt with in