Columnar: chunk_group metadata table

src/backend/columnar/cstore_metadata_tables.c

@@ -86,6 +86,7 @@ static Oid ColumnarStripeIndexRelationId(void);
 static Oid ColumnarOptionsRelationId(void);
 static Oid ColumnarOptionsIndexRegclass(void);
 static Oid ColumnarChunkRelationId(void);
+static Oid ColumnarChunkGroupRelationId(void);
 static Oid ColumnarChunkIndexRelationId(void);
 static Oid ColumnarNamespaceId(void);
 static ModifyState * StartModifyRelation(Relation rel);
@@ -139,6 +140,13 @@ typedef FormData_columnar_options *Form_columnar_options;
 #define Anum_columnar_stripe_chunk_row_count 7
 #define Anum_columnar_stripe_row_count 8
 
+/* constants for columnar.chunk_group */
+#define Natts_columnar_chunkgroup 4
+#define Anum_columnar_chunkgroup_storageid 1
+#define Anum_columnar_chunkgroup_stripe 2
+#define Anum_columnar_chunkgroup_chunk 3
+#define Anum_columnar_chunkgroup_row_count 4
+
 /* constants for columnar.chunk */
 #define Natts_columnar_chunk 14
 #define Anum_columnar_chunk_storageid 1
@@ -462,6 +470,44 @@ SaveStripeSkipList(RelFileNode relfilenode, uint64 stripe, StripeSkipList *chunk
 }
 
 
+/*
+ * SaveChunkGroups saves the metadata for given chunk groups in columnar.chunk_group.
+ */
+void
+SaveChunkGroups(RelFileNode relfilenode, uint64 stripe,
+				List *chunkGroupRowCounts)
+{
+	ColumnarMetapage *metapage = ReadMetapage(relfilenode, false);
+	Oid columnarChunkGroupOid = ColumnarChunkGroupRelationId();
+	Relation columnarChunkGroup = table_open(columnarChunkGroupOid, RowExclusiveLock);
+	ModifyState *modifyState = StartModifyRelation(columnarChunkGroup);
+
+	ListCell *lc = NULL;
+	int chunkId = 0;
+
+	foreach(lc, chunkGroupRowCounts)
+	{
+		int64 rowCount = lfirst_int(lc);
+		Datum values[Natts_columnar_chunkgroup] = {
+			UInt64GetDatum(metapage->storageId),
+			Int64GetDatum(stripe),
+			Int32GetDatum(chunkId),
+			Int64GetDatum(rowCount)
+		};
+
+		bool nulls[Natts_columnar_chunkgroup] = { false };
+
+		InsertTupleAndEnforceConstraints(modifyState, values, nulls);
+		chunkId++;
+	}
+
+	FinishModifyRelation(modifyState);
+	table_close(columnarChunkGroup, NoLock);
+
+	CommandCounterIncrement();
+}
+
+
 /*
  * ReadStripeSkipList fetches chunk metadata for a given stripe.
  */
@@ -1113,6 +1159,17 @@ ColumnarChunkRelationId(void)
 }
 
 
+/*
+ * ColumnarChunkGroupRelationId returns relation id of columnar.chunk_group.
+ * TODO: should we cache this similar to citus?
+ */
+static Oid
+ColumnarChunkGroupRelationId(void)
+{
+	return get_relname_relid("chunk_group", ColumnarNamespaceId());
+}
+
+
 /*
  * ColumnarChunkIndexRelationId returns relation id of columnar.chunk_pkey.
  * TODO: should we cache this similar to citus?

src/backend/columnar/cstore_writer.c

@@ -45,6 +45,8 @@ struct TableWriteState
 	ColumnarOptions options;
 	ChunkData *chunkData;
 
+	List *chunkGroupRowCounts;
+
 	/*
 	 * compressionBuffer buffer is used as temporary storage during
 	 * data value compression operation. It is kept here to minimize
@@ -548,11 +550,15 @@ FlushStripe(TableWriteState *writeState)
 		}
 	}
 
-	/* create skip list and footer buffers */
+	SaveChunkGroups(writeState->relfilenode,
+					stripeMetadata.id,
+					writeState->chunkGroupRowCounts);
 	SaveStripeSkipList(writeState->relfilenode,
 					   stripeMetadata.id,
 					   stripeSkipList, tupleDescriptor);
 
+	writeState->chunkGroupRowCounts = NIL;
+
 	relation_close(relation, NoLock);
 }
 
@@ -640,6 +646,9 @@ SerializeChunkData(TableWriteState *writeState, uint32 chunkIndex, uint32 rowCou
 	const uint32 columnCount = stripeBuffers->columnCount;
 	StringInfo compressionBuffer = writeState->compressionBuffer;
 
+	writeState->chunkGroupRowCounts =
+		lappend_int(writeState->chunkGroupRowCounts, rowCount);
+
 	/* serialize exist values, data values are already serialized */
 	for (columnIndex = 0; columnIndex < columnCount; columnIndex++)
 	{

src/backend/columnar/sql/columnar--9.5-1--10.0-1.sql

@@ -29,6 +29,17 @@ CREATE TABLE stripe (
 
 COMMENT ON TABLE stripe IS 'Columnar per stripe metadata';
 
+CREATE TABLE chunk_group (
+    storageid bigint NOT NULL,
+    stripeid bigint NOT NULL,
+    chunkid int NOT NULL,
+    row_count bigint NOT NULL,
+    PRIMARY KEY (storageid, stripeid, chunkid),
+    FOREIGN KEY (storageid, stripeid) REFERENCES stripe(storageid, stripeid) ON DELETE CASCADE
+);
+
+COMMENT ON TABLE chunk_group IS 'Columnar chunk group metadata';
+
 CREATE TABLE chunk (
     storageid bigint NOT NULL,
     stripeid bigint NOT NULL,
@@ -45,7 +56,7 @@ CREATE TABLE chunk (
     value_compression_level int NOT NULL,
     value_decompressed_length bigint NOT NULL,
     PRIMARY KEY (storageid, stripeid, attnum, chunkid),
-    FOREIGN KEY (storageid, stripeid) REFERENCES stripe(storageid, stripeid) ON DELETE CASCADE
+    FOREIGN KEY (storageid, stripeid, chunkid) REFERENCES chunk_group(storageid, stripeid, chunkid) ON DELETE CASCADE
 ) WITH (user_catalog_table = true);
 
 COMMENT ON TABLE chunk IS 'Columnar per chunk metadata';

src/backend/columnar/sql/downgrades/columnar--10.0-1--9.5-1.sql

@@ -30,6 +30,7 @@ END IF;
 END$proc$;
 
 DROP TABLE chunk;
+DROP TABLE chunk_group;
 DROP TABLE stripe;
 DROP TABLE options;
 DROP SEQUENCE storageid_seq;

src/include/columnar/columnar.h

@@ -287,6 +287,8 @@ extern StripeMetadata ReserveStripe(Relation rel, uint64 size,
 extern void SaveStripeSkipList(RelFileNode relfilenode, uint64 stripe,
 							   StripeSkipList *stripeSkipList,
 							   TupleDesc tupleDescriptor);
+extern void SaveChunkGroups(RelFileNode relfilenode, uint64 stripe,
+							List *chunkGroupRowCounts);
 extern StripeSkipList * ReadStripeSkipList(RelFileNode relfilenode, uint64 stripe,
 										   TupleDesc tupleDescriptor,
 										   uint32 chunkCount);

src/test/regress/expected/am_create.out

@@ -42,3 +42,18 @@ EXCEPTION WHEN invalid_parameter_value THEN
    return false;
 END;
 $$ LANGUAGE plpgsql;
+-- are chunk groups and chunks consistent?
+CREATE view chunk_group_consistency AS
+WITH a as (
+   SELECT storageid, stripeid, chunkid, min(value_count) as row_count
+   FROM columnar.chunk
+   GROUP BY 1,2,3
+), b as (
+   SELECT storageid, stripeid, chunkid, max(value_count) as row_count
+   FROM columnar.chunk
+   GROUP BY 1,2,3
+), c as (
+   (TABLE a EXCEPT TABLE b) UNION (TABLE b EXCEPT TABLE a) UNION
+   (TABLE a EXCEPT TABLE columnar.chunk_group) UNION (TABLE columnar.chunk_group EXCEPT TABLE a)
+)
+SELECT count(*) = 0 AS consistent FROM c;

src/test/regress/expected/am_insert.out

@@ -45,6 +45,12 @@ select count(*) from test_insert_command;
      3
 (1 row)
 
+SELECT * FROM chunk_group_consistency;
+ consistent
+---------------------------------------------------------------------
+ t
+(1 row)
+
 drop table test_insert_command_data;
 drop table test_insert_command;
 -- test long attribute value insertion
@@ -61,6 +67,12 @@ CREATE TABLE test_cstore_long_text(int_val int, text_val text)
 USING columnar;
 -- store long text in cstore table
 INSERT INTO test_cstore_long_text SELECT * FROM test_long_text;
+SELECT * FROM chunk_group_consistency;
+ consistent
+---------------------------------------------------------------------
+ t
+(1 row)
+
 -- drop source table to remove original text from toast
 DROP TABLE test_long_text;
 -- check if text data is still available in cstore table
@@ -129,5 +141,11 @@ FROM test_toast_columnar;
            5004 |           5004 |           5004 |           5004
 (1 row)
 
+SELECT * FROM chunk_group_consistency;
+ consistent
+---------------------------------------------------------------------
+ t
+(1 row)
+
 DROP TABLE test_toast_row;
 DROP TABLE test_toast_columnar;

src/test/regress/expected/am_recursive.out

@@ -72,6 +72,12 @@ SELECT * FROM t2;
  5 | 6
 (5 rows)
 
+SELECT * FROM chunk_group_consistency;
+ consistent
+---------------------------------------------------------------------
+ t
+(1 row)
+
 TRUNCATE t1;
 TRUNCATE t2;
 --
@@ -101,6 +107,12 @@ SELECT * FROM t2;
  3 | 0
 (3 rows)
 
+SELECT * FROM chunk_group_consistency;
+ consistent
+---------------------------------------------------------------------
+ t
+(1 row)
+
 TRUNCATE t1;
 TRUNCATE t2;
 --
@@ -125,6 +137,12 @@ SELECT * FROM t1 ORDER BY a, b;
  5 | 10
 (10 rows)
 
+SELECT * FROM chunk_group_consistency;
+ consistent
+---------------------------------------------------------------------
+ t
+(1 row)
+
 TRUNCATE t1;
 TRUNCATE t2;
 --
@@ -165,6 +183,12 @@ SELECT * FROM t2 ORDER BY a, b;
  5 | 5
 (5 rows)
 
+SELECT * FROM chunk_group_consistency;
+ consistent
+---------------------------------------------------------------------
+ t
+(1 row)
+
 TRUNCATE t1, t2, t3, t4;
 --
 -- INSERT into the same relation that was INSERTed into in the UDF
@@ -204,6 +228,12 @@ SELECT * FROM t3 ORDER BY a, b;
 ---------------------------------------------------------------------
 (0 rows)
 
+SELECT * FROM chunk_group_consistency;
+ consistent
+---------------------------------------------------------------------
+ t
+(1 row)
+
 DROP FUNCTION g(int), g2(int);
 TRUNCATE t1, t2, t3, t4;
 --
@@ -248,5 +278,11 @@ SELECT * FROM t1 ORDER BY a, b;
  23 | 46
 (10 rows)
 
+SELECT * FROM chunk_group_consistency;
+ consistent
+---------------------------------------------------------------------
+ t
+(1 row)
+
 DROP FUNCTION f(int);
 DROP TABLE t1, t2, t3, t4;

src/test/regress/expected/am_truncate.out

@@ -37,7 +37,19 @@ SELECT * FROM columnar_truncate_test;
  10 | 10
 (10 rows)
 
+SELECT * FROM chunk_group_consistency;
+ consistent
+---------------------------------------------------------------------
+ t
+(1 row)
+
 TRUNCATE TABLE columnar_truncate_test;
+SELECT * FROM chunk_group_consistency;
+ consistent
+---------------------------------------------------------------------
+ t
+(1 row)
+
 SELECT * FROM columnar_truncate_test;
  a | b
 ---------------------------------------------------------------------
@@ -118,12 +130,24 @@ SELECT * from columnar_truncate_test_regular;
  20 | 20
 (11 rows)
 
+SELECT * FROM chunk_group_consistency;
+ consistent
+---------------------------------------------------------------------
+ t
+(1 row)
+
 -- make sure multi truncate works
 -- notice that the same table might be repeated
 TRUNCATE TABLE columnar_truncate_test,
 			   columnar_truncate_test_regular,
 			   columnar_truncate_test_second,
    			   columnar_truncate_test;
+SELECT * FROM chunk_group_consistency;
+ consistent
+---------------------------------------------------------------------
+ t
+(1 row)
+
 SELECT * from columnar_truncate_test;
  a | b
 ---------------------------------------------------------------------
@@ -267,6 +291,12 @@ SELECT count(*) FROM truncate_schema.truncate_tbl;
 (1 row)
 
 \c - :current_user
+SELECT * FROM chunk_group_consistency;
+ consistent
+---------------------------------------------------------------------
+ t
+(1 row)
+
 -- cleanup
 DROP SCHEMA truncate_schema CASCADE;
 NOTICE:  drop cascades to table truncate_schema.truncate_tbl

src/test/regress/expected/am_vacuum.out

@@ -27,6 +27,12 @@ SELECT count(*) FROM t_stripes;
 
 -- vacuum full should merge stripes together
 VACUUM FULL t;
+SELECT * FROM chunk_group_consistency;
+ consistent
+---------------------------------------------------------------------
+ t
+(1 row)
+
 SELECT sum(a), sum(b) FROM t;
  sum | sum
 ---------------------------------------------------------------------
@@ -60,6 +66,12 @@ SELECT count(*) FROM t_stripes;
 (1 row)
 
 VACUUM FULL t;
+SELECT * FROM chunk_group_consistency;
+ consistent
+---------------------------------------------------------------------
+ t
+(1 row)
+
 SELECT sum(a), sum(b) FROM t;
    sum   |   sum
 ---------------------------------------------------------------------
@@ -203,6 +215,12 @@ compression rate: 1.25x
 total row count: 5530, stripe count: 5, average rows per stripe: 1106
 chunk count: 7, containing data for dropped columns: 0, none compressed: 5, pglz compressed: 2
 
+SELECT * FROM chunk_group_consistency;
+ consistent
+---------------------------------------------------------------------
+ t
+(1 row)
+
 SELECT count(*) FROM t;
  count
 ---------------------------------------------------------------------
@@ -239,6 +257,12 @@ compression rate: 1.96x
 total row count: 7030, stripe count: 4, average rows per stripe: 1757
 chunk count: 8, containing data for dropped columns: 0, none compressed: 2, pglz compressed: 6
 
+SELECT * FROM chunk_group_consistency;
+ consistent
+---------------------------------------------------------------------
+ t
+(1 row)
+
 DROP TABLE t;
 DROP VIEW t_stripes;
 -- Make sure we cleaned the metadata for t too
@@ -262,4 +286,10 @@ compression rate: 33.71x
 total row count: 1000000, stripe count: 1, average rows per stripe: 1000000
 chunk count: 30, containing data for dropped columns: 0, pglz compressed: 30
 
+SELECT * FROM chunk_group_consistency;
+ consistent
+---------------------------------------------------------------------
+ t
+(1 row)
+
 DROP TABLE t;

src/test/regress/expected/multi_extension.out

@@ -507,12 +507,13 @@ SELECT * FROM print_extension_changes();
                                                                                  | schema columnar
                                                                                  | sequence columnar.storageid_seq
                                                                                  | table columnar.chunk
+                                                                                 | table columnar.chunk_group
                                                                                  | table columnar.options
                                                                                  | table columnar.stripe
                                                                                  | view citus_shards
                                                                                  | view citus_tables
                                                                                  | view time_partitions
-(66 rows)
+(67 rows)
 
 DROP TABLE prev_objects, extension_diff;
 -- show running version

src/test/regress/expected/multi_extension_0.out

@@ -503,12 +503,13 @@ SELECT * FROM print_extension_changes();
                                                                                  | schema columnar
                                                                                  | sequence columnar.storageid_seq
                                                                                  | table columnar.chunk
+                                                                                 | table columnar.chunk_group
                                                                                  | table columnar.options
                                                                                  | table columnar.stripe
                                                                                  | view citus_shards
                                                                                  | view citus_tables
                                                                                  | view time_partitions
-(62 rows)
+(63 rows)
 
 DROP TABLE prev_objects, extension_diff;
 -- show running version

src/test/regress/expected/upgrade_list_citus_objects.out

@@ -214,6 +214,7 @@ ORDER BY 1;
  sequence pg_dist_shardid_seq
  table citus.pg_dist_object
  table columnar.chunk
+ table columnar.chunk_group
  table columnar.options
  table columnar.stripe
  table pg_dist_authinfo
@@ -241,5 +242,5 @@ ORDER BY 1;
  view citus_worker_stat_activity
  view pg_dist_shard_placement
  view time_partitions
-(225 rows)
+(226 rows)
 

src/test/regress/expected/upgrade_list_citus_objects_0.out

@@ -210,6 +210,7 @@ ORDER BY 1;
  sequence pg_dist_shardid_seq
  table citus.pg_dist_object
  table columnar.chunk
+ table columnar.chunk_group
  table columnar.options
  table columnar.stripe
  table pg_dist_authinfo
@@ -237,5 +238,5 @@ ORDER BY 1;
  view citus_worker_stat_activity
  view pg_dist_shard_placement
  view time_partitions
-(221 rows)
+(222 rows)
 

src/test/regress/input/am_load.source

@@ -43,4 +43,6 @@ speed of light,2.997e8
 
 SELECT * FROM famous_constants ORDER BY id, name;
 
+SELECT * FROM chunk_group_consistency;
+
 DROP TABLE famous_constants;

src/test/regress/output/am_load.source

@@ -39,4 +39,10 @@ SELECT * FROM famous_constants ORDER BY id, name;
     | speed of light | 2.997e+08
 (8 rows)
 
+SELECT * FROM chunk_group_consistency;
+ consistent
+---------------------------------------------------------------------
+ t
+(1 row)
+
 DROP TABLE famous_constants;

src/test/regress/sql/am_create.sql

@@ -44,3 +44,20 @@ EXCEPTION WHEN invalid_parameter_value THEN
    return false;
 END;
 $$ LANGUAGE plpgsql;
+
+
+-- are chunk groups and chunks consistent?
+CREATE view chunk_group_consistency AS
+WITH a as (
+   SELECT storageid, stripeid, chunkid, min(value_count) as row_count
+   FROM columnar.chunk
+   GROUP BY 1,2,3
+), b as (
+   SELECT storageid, stripeid, chunkid, max(value_count) as row_count
+   FROM columnar.chunk
+   GROUP BY 1,2,3
+), c as (
+   (TABLE a EXCEPT TABLE b) UNION (TABLE b EXCEPT TABLE a) UNION
+   (TABLE a EXCEPT TABLE columnar.chunk_group) UNION (TABLE columnar.chunk_group EXCEPT TABLE a)
+)
+SELECT count(*) = 0 AS consistent FROM c;

src/test/regress/sql/am_insert.sql

@@ -22,6 +22,8 @@ select count(*) from test_insert_command_data;
 insert into test_insert_command select * from test_insert_command_data;
 select count(*) from test_insert_command;
 
+SELECT * FROM chunk_group_consistency;
+
 drop table test_insert_command_data;
 drop table test_insert_command;
 
@@ -43,6 +45,8 @@ USING columnar;
 -- store long text in cstore table
 INSERT INTO test_cstore_long_text SELECT * FROM test_long_text;
 
+SELECT * FROM chunk_group_consistency;
+
 -- drop source table to remove original text from toast
 DROP TABLE test_long_text;
 
@@ -95,5 +99,7 @@ SELECT
   pg_column_size(external), pg_column_size(extended)
 FROM test_toast_columnar;
 
+SELECT * FROM chunk_group_consistency;
+
 DROP TABLE test_toast_row;
 DROP TABLE test_toast_columnar;

src/test/regress/sql/am_recursive.sql

@@ -39,6 +39,8 @@ INSERT INTO t2 SELECT t.a, t.a+1 FROM t;
 SELECT * FROM t1;
 SELECT * FROM t2;
 
+SELECT * FROM chunk_group_consistency;
+
 TRUNCATE t1;
 TRUNCATE t2;
 
@@ -55,6 +57,8 @@ INSERT INTO t2 SELECT i, (select count(*) from t1) FROM generate_series(1, 3) i;
 SELECT * FROM t1;
 SELECT * FROM t2;
 
+SELECT * FROM chunk_group_consistency;
+
 TRUNCATE t1;
 TRUNCATE t2;
 
@@ -68,6 +72,8 @@ INSERT INTO t1 SELECT t.a, t.a+1 FROM t;
 
 SELECT * FROM t1 ORDER BY a, b;
 
+SELECT * FROM chunk_group_consistency;
+
 TRUNCATE t1;
 TRUNCATE t2;
 
@@ -99,6 +105,8 @@ INSERT INTO t4 SELECT i, g2(i) FROM generate_series(1, 5) i;
 
 SELECT * FROM t2 ORDER BY a, b;
 
+SELECT * FROM chunk_group_consistency;
+
 TRUNCATE t1, t2, t3, t4;
 
 --
@@ -113,6 +121,8 @@ SELECT * FROM t3 ORDER BY a, b;
 ((table t1) except (table t3)) union ((table t3) except (table t1));
 ((table t2) except (table t4)) union ((table t4) except (table t2));
 
+SELECT * FROM chunk_group_consistency;
+
 DROP FUNCTION g(int), g2(int);
 TRUNCATE t1, t2, t3, t4;
 
@@ -138,6 +148,8 @@ SELECT f(0), f(20);
 
 SELECT * FROM t1 ORDER BY a, b;
 
+SELECT * FROM chunk_group_consistency;
+
 DROP FUNCTION f(int);
 DROP TABLE t1, t2, t3, t4;
 

src/test/regress/sql/am_truncate.sql

@@ -25,8 +25,12 @@ set columnar.compression to default;
 -- query rows
 SELECT * FROM columnar_truncate_test;
 
+SELECT * FROM chunk_group_consistency;
+
 TRUNCATE TABLE columnar_truncate_test;
 
+SELECT * FROM chunk_group_consistency;
+
 SELECT * FROM columnar_truncate_test;
 
 SELECT COUNT(*) from columnar_truncate_test;
@@ -47,6 +51,8 @@ SELECT * from columnar_truncate_test_second;
 
 SELECT * from columnar_truncate_test_regular;
 
+SELECT * FROM chunk_group_consistency;
+
 -- make sure multi truncate works
 -- notice that the same table might be repeated
 TRUNCATE TABLE columnar_truncate_test,
@@ -54,6 +60,8 @@ TRUNCATE TABLE columnar_truncate_test,
 			   columnar_truncate_test_second,
    			   columnar_truncate_test;
 
+SELECT * FROM chunk_group_consistency;
+
 SELECT * from columnar_truncate_test;
 SELECT * from columnar_truncate_test_second;
 SELECT * from columnar_truncate_test_regular;
@@ -136,6 +144,8 @@ TRUNCATE TABLE truncate_schema.truncate_tbl;
 SELECT count(*) FROM truncate_schema.truncate_tbl;
 \c - :current_user
 
+SELECT * FROM chunk_group_consistency;
+
 -- cleanup
 DROP SCHEMA truncate_schema CASCADE;
 DROP USER truncate_user;

src/test/regress/sql/am_vacuum.sql

@@ -20,6 +20,8 @@ SELECT count(*) FROM t_stripes;
 -- vacuum full should merge stripes together
 VACUUM FULL t;
 
+SELECT * FROM chunk_group_consistency;
+
 SELECT sum(a), sum(b) FROM t;
 SELECT count(*) FROM t_stripes;
 
@@ -32,6 +34,8 @@ SELECT count(*) FROM t_stripes;
 
 VACUUM FULL t;
 
+SELECT * FROM chunk_group_consistency;
+
 SELECT sum(a), sum(b) FROM t;
 SELECT count(*) FROM t_stripes;
 
@@ -92,6 +96,8 @@ COMMIT;
 
 VACUUM VERBOSE t;
 
+SELECT * FROM chunk_group_consistency;
+
 SELECT count(*) FROM t;
 
 -- check that we report chunks with data for dropped columns
@@ -108,6 +114,8 @@ SELECT alter_columnar_table_set('t', compression => 'pglz');
 VACUUM FULL t;
 VACUUM VERBOSE t;
 
+SELECT * FROM chunk_group_consistency;
+
 DROP TABLE t;
 DROP VIEW t_stripes;
 
@@ -123,4 +131,6 @@ INSERT INTO t SELECT 1, 'a', 'xyz' FROM generate_series(1, 1000000) i;
 
 VACUUM VERBOSE t;
 
+SELECT * FROM chunk_group_consistency;
+
 DROP TABLE t;