Implement ALTER TABLE ... RENAME TO ...

The implementation was already mostly in place, but the code was protected
by a principled check against the operation. Turns out there's a nasty
concurrency bug though with long identifier names, much as in #1664.

To prevent deadlocks from happening, we could either review the DDL
transaction management in shards and placements, or we can simply reject
names with (NAMEDATALEN - 1) chars or more — that's because of the
PostgreSQL array types being created with a one-char prefix: '_'.

src/backend/distributed/executor/multi_utility.c

@@ -2740,12 +2740,7 @@ ErrorIfUnsupportedRenameStmt(RenameStmt *renameStmt)
 {
 	Assert(IsAlterTableRenameStmt(renameStmt));
 
-	if (renameStmt->renameType == OBJECT_TABLE)
+	if (renameStmt->renameType == OBJECT_TABCONSTRAINT)
-	{
-		ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-						errmsg("renaming distributed tables is currently unsupported")));
-	}
-	else if (renameStmt->renameType == OBJECT_TABCONSTRAINT)
 	{
 		ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 						errmsg("renaming constraints belonging to distributed tables is "

src/backend/distributed/relay/relay_event_utility.c

@@ -388,12 +388,37 @@ RelayEventExtendNames(Node *parseTree, char *schemaName, uint64 shardId)
 				char **oldRelationName = &(renameStmt->relation->relname);
 				char **newRelationName = &(renameStmt->newname);
 				char **objectSchemaName = &(renameStmt->relation->schemaname);
+				int newRelationNameLength;
 
 				/* prefix with schema name if it is not added already */
 				SetSchemaNameIfNotExist(objectSchemaName, schemaName);
 
 				AppendShardIdToName(oldRelationName, shardId);
 				AppendShardIdToName(newRelationName, shardId);
+
+				/*
+				 * PostgreSQL creates array types for each ordinary table, with
+				 * the same name plus a prefix of '_'.
+				 *
+				 * ALTER TABLE ... RENAME TO ... also renames the underlying
+				 * array type, and the DDL is run in parallel connections over
+				 * all the placements and shards at once. Concurrent access
+				 * here deadlocks.
+				 *
+				 * Let's provide an easier to understand error message here
+				 * than the deadlock one.
+				 *
+				 * See also https://github.com/citusdata/citus/issues/1664
+				 */
+				newRelationNameLength = strlen(*newRelationName);
+				if (newRelationNameLength >= (NAMEDATALEN - 1))
+				{
+					ereport(ERROR,
+							(errcode(ERRCODE_NAME_TOO_LONG),
+							 errmsg(
+								 "shard name %s exceeds %d characters",
+								 *newRelationName, NAMEDATALEN - 1)));
+				}
 			}
 			else if (objectType == OBJECT_COLUMN || objectType == OBJECT_TRIGGER)
 			{

src/test/regress/expected/multi_name_lengths.out

@@ -113,7 +113,8 @@ SELECT "Constraint", "Definition" FROM table_checks WHERE relid='public.name_len
 \c - - - :master_port
 -- Placeholders for RENAME operations
 ALTER TABLE name_lengths RENAME TO name_len_12345678901234567890123456789012345678901234567890;
-ERROR:  renaming distributed tables is currently unsupported
+ERROR:  shard name name_len_12345678901234567890123456789012345678_fcd8ab6f_225002 exceeds 63 characters
+CONTEXT:  while executing command on localhost:57638
 ALTER TABLE name_lengths RENAME CONSTRAINT unique_12345678901234567890123456789012345678901234567890 TO unique2_12345678901234567890123456789012345678901234567890;
 ERROR:  renaming constraints belonging to distributed tables is currently unsupported
 -- Verify that CREATE INDEX on already distributed table has proper shard names.

src/test/regress/expected/multi_reference_table.out

@@ -1382,12 +1382,13 @@ SELECT "Column", "Type", "Modifiers" FROM table_desc WHERE relid='public.referen
 (0 rows)
 
 \c - - - :master_port
--- as we expect, renaming and setting WITH OIDS does not work for reference tables
+-- as we expect, setting WITH OIDS does not work for reference tables
-ALTER TABLE reference_table_ddl RENAME TO reference_table_ddl_test;
-ERROR:  renaming distributed tables is currently unsupported
 ALTER TABLE reference_table_ddl SET WITH OIDS;
 ERROR:  alter table command is currently unsupported
 DETAIL:  Only ADD|DROP COLUMN, SET|DROP NOT NULL, SET|DROP DEFAULT, ADD|DROP CONSTRAINT, ATTACH|DETACH PARTITION and TYPE subcommands are supported.
+-- now test the renaming of the table, and back to the expected name
+ALTER TABLE reference_table_ddl RENAME TO reference_table_ddl_test;
+ALTER TABLE reference_table_ddl_test RENAME TO reference_table_ddl;
 -- now test reference tables against some helper UDFs that Citus provides
 -- cannot delete / drop shards from a reference table
 SELECT master_apply_delete_command('DELETE FROM reference_table_ddl');

src/test/regress/input/multi_alter_table_statements.source

@@ -148,9 +148,8 @@ ALTER TABLE lineitem_alter ADD COLUMN new_column non_existent_type;
 ALTER TABLE lineitem_alter ALTER COLUMN null_column SET NOT NULL;
 ALTER TABLE lineitem_alter ALTER COLUMN l_partkey SET DEFAULT 'a';
 
--- Verify that we error out on non-column RENAME statements
+-- Verify that we error out on RENAME CONSTRAINT statement
 
-ALTER TABLE lineitem_alter RENAME TO lineitem_renamed;
 ALTER TABLE lineitem_alter RENAME CONSTRAINT constraint_a TO constraint_b;
 
 -- Verify that IF EXISTS works as expected with RENAME statements
@@ -356,10 +355,30 @@ FROM
 ORDER BY attnum;
 \c - - - :master_port
 
+-- verify that we can rename distributed tables
+SHOW citus.enable_ddl_propagation;
+ALTER TABLE lineitem_alter RENAME TO lineitem_renamed;
+
+-- verify rename is performed
+SELECT relname FROM pg_class WHERE relname = 'lineitem_renamed';
+
+-- show rename worked on one worker, too
+\c - - - :worker_1_port
+SELECT relname FROM pg_class WHERE relname LIKE 'lineitem_renamed%'  ORDER BY relname;
+\c - - - :master_port
+
+-- revert it to original name
+ALTER TABLE lineitem_renamed RENAME TO lineitem_alter;
+
+-- show rename worked on one worker, too
+\c - - - :worker_1_port
+SELECT relname FROM pg_class WHERE relname LIKE 'lineitem_alter%' ORDER BY relname;
+\c - - - :master_port
+
 -- verify that we don't intercept DDL commands if propagation is turned off
 SET citus.enable_ddl_propagation to false;
 
--- table rename statement can be performed now
+-- table rename statement can be performed on the coordinator only now
 ALTER TABLE lineitem_alter RENAME TO lineitem_renamed;
 -- verify rename is performed
 SELECT relname FROM pg_class WHERE relname = 'lineitem_alter' or relname = 'lineitem_renamed';

src/test/regress/output/multi_alter_table_statements.source

@@ -377,9 +377,7 @@ ERROR:  column "null_column" contains null values
 CONTEXT:  while executing command on localhost:57638
 ALTER TABLE lineitem_alter ALTER COLUMN l_partkey SET DEFAULT 'a';
 ERROR:  invalid input syntax for integer: "a"
--- Verify that we error out on non-column RENAME statements
+-- Verify that we error out on RENAME CONSTRAINT statement
-ALTER TABLE lineitem_alter RENAME TO lineitem_renamed;
-ERROR:  renaming distributed tables is currently unsupported
 ALTER TABLE lineitem_alter RENAME CONSTRAINT constraint_a TO constraint_b;
 ERROR:  renaming constraints belonging to distributed tables is currently unsupported
 -- Verify that IF EXISTS works as expected with RENAME statements
@@ -783,10 +781,72 @@ ORDER BY attnum;
  ........pg.dropped.24........ | -
 (30 rows)
 
+\c - - - :master_port
+-- verify that we can rename distributed tables
+SHOW citus.enable_ddl_propagation;
+ citus.enable_ddl_propagation 
+------------------------------
+ on
+(1 row)
+
+ALTER TABLE lineitem_alter RENAME TO lineitem_renamed;
+-- verify rename is performed
+SELECT relname FROM pg_class WHERE relname = 'lineitem_renamed';
+     relname      
+------------------
+ lineitem_renamed
+(1 row)
+
+-- show rename worked on one worker, too
+\c - - - :worker_1_port
+SELECT relname FROM pg_class WHERE relname LIKE 'lineitem_renamed%'  ORDER BY relname;
+         relname         
+-------------------------
+ lineitem_renamed_220000
+ lineitem_renamed_220001
+ lineitem_renamed_220002
+ lineitem_renamed_220003
+ lineitem_renamed_220004
+ lineitem_renamed_220005
+ lineitem_renamed_220006
+ lineitem_renamed_220007
+ lineitem_renamed_220008
+ lineitem_renamed_220010
+ lineitem_renamed_220011
+ lineitem_renamed_220012
+ lineitem_renamed_220013
+ lineitem_renamed_220014
+(14 rows)
+
+\c - - - :master_port
+-- revert it to original name
+ALTER TABLE lineitem_renamed RENAME TO lineitem_alter;
+-- show rename worked on one worker, too
+\c - - - :worker_1_port
+SELECT relname FROM pg_class WHERE relname LIKE 'lineitem_alter%' ORDER BY relname;
+        relname        
+-----------------------
+ lineitem_alter_220000
+ lineitem_alter_220001
+ lineitem_alter_220002
+ lineitem_alter_220003
+ lineitem_alter_220004
+ lineitem_alter_220005
+ lineitem_alter_220006
+ lineitem_alter_220007
+ lineitem_alter_220008
+ lineitem_alter_220009
+ lineitem_alter_220010
+ lineitem_alter_220011
+ lineitem_alter_220012
+ lineitem_alter_220013
+ lineitem_alter_220014
+(15 rows)
+
 \c - - - :master_port
 -- verify that we don't intercept DDL commands if propagation is turned off
 SET citus.enable_ddl_propagation to false;
--- table rename statement can be performed now
+-- table rename statement can be performed on the coordinator only now
 ALTER TABLE lineitem_alter RENAME TO lineitem_renamed;
 -- verify rename is performed
 SELECT relname FROM pg_class WHERE relname = 'lineitem_alter' or relname = 'lineitem_renamed';

src/test/regress/sql/multi_reference_table.sql

@@ -872,10 +872,13 @@ SELECT "Column", "Type", "Modifiers" FROM table_desc WHERE relid='public.referen
 \di reference_index_2*
 \c - - - :master_port
 
--- as we expect, renaming and setting WITH OIDS does not work for reference tables
+-- as we expect, setting WITH OIDS does not work for reference tables
-ALTER TABLE reference_table_ddl RENAME TO reference_table_ddl_test;
 ALTER TABLE reference_table_ddl SET WITH OIDS;
 
+-- now test the renaming of the table, and back to the expected name
+ALTER TABLE reference_table_ddl RENAME TO reference_table_ddl_test;
+ALTER TABLE reference_table_ddl_test RENAME TO reference_table_ddl;
+
 -- now test reference tables against some helper UDFs that Citus provides
 
 -- cannot delete / drop shards from a reference table