# Enhanced Toast相关DDL操作
**Enhanced Toast** **表的创建**
建表时指定Toast表的存储类型为Enhanced Toast或者Toast：
```
gaussdb=#  CREATE TABLE test_toast (id int, content text) with(toast.toast_storage_type=toast);
CREATE TABLE
gaussdb=#  \d+ test_toast
                       Table "public.test_toast"
 Column  |  Type   | Modifiers | Storage  | Stats target | Description
---------+---------+-----------+----------+--------------+-------------
 id      | integer |           | plain    |              |
 content | text    |           | extended |              |
Has OIDs: no
Distribute By: HASH(a)
Location Nodes: ALL DATANODES
Options: orientation=row, compression=no, storage_type=USTORE, segment=off, toast.storage_type=USTORE, toast.toast_storage_type=toast
gaussdb=#  DROP TABLE test_toast;
DROP TABLE
gaussdb=#  CREATE TABLE test_toast (id int, content text) with(toast.toast_storage_type=enhanced_toast);
CREATE TABLE
gaussdb=#  \d+ test_toast
                       Table "public.test_toast"
 Column  |  Type   | Modifiers | Storage  | Stats target | Description
---------+---------+-----------+----------+--------------+-------------
 id      | integer |           | plain    |              |
 content | text    |           | extended |              |
Has OIDs: no
Distribute By: HASH(a)
Location Nodes: ALL DATANODES
Options: orientation=row, compression=no, storage_type=USTORE, segment=off, toast.storage_type=USTORE, toast.toast_storage_type=enhanced_toast
gaussdb=#  DROP TABLE test_toast;
DROP TABLE
```
建表时不指定线外存储表的类型，则创建线外存储表类型依赖于GUC参数enable_enhance_toast_table：
```
-- 根据“Enhanced Toast使用”章节打开GUC
gaussdb=#  show enable_enhance_toast_table;
 enable_enhance_toast_table
----------------------------
 on
(1 row)
gaussdb=#  CREATE TABLE test_toast (id int, content text);
CREATE TABLE
gaussdb=#   \d+ test_toast
                       Table "public.test_toast"
 Column  |  Type   | Modifiers | Storage  | Stats target | Description
---------+---------+-----------+----------+--------------+-------------
 id      | integer |           | plain    |              |
 content | text    |           | extended |              |
Has OIDs: no
Distribute By: HASH(a)
Location Nodes: ALL DATANODES
Options: orientation=row, compression=no, storage_type=USTORE, segment=off, toast.storage_type=USTORE, toast.toast_storage_type=enhanced_toast
gaussdb=#   DROP TABLE test_toast;
DROP TABLE
gaussdb=#  SET enable_enhance_toast_table = off;
SET
gaussdb=#  show enable_enhance_toast_table;
 enable_enhance_toast_table
----------------------------
 off
(1 row)
gaussdb=#   CREATE TABLE test_toast (id int, content text);
CREATE TABLE
gaussdb=#  \d+ test_toast
                       Table "public.test_toast"
 Column  |  Type   | Modifiers | Storage  | Stats target | Description
---------+---------+-----------+----------+--------------+-------------
 id      | integer |           | plain    |              |
 content | text    |           | extended |              |
Has OIDs: no
Distribute By: HASH(a)
Location Nodes: ALL DATANODES
Options: orientation=row, compression=no, storage_type=USTORE, segment=off, toast.storage_type=USTORE, toast.toast_storage_type=toast
gaussdb=#  DROP TABLE test_toast;
DROP TABLE
```
**线外存储表结构的升级**
当GUC参数"enable_enhance_toast_table=on"时，线外存储表支持通过Vacuum Full操作将Toast升级为Enhanced Toast结构。
```
gaussdb=#   CREATE TABLE test_toast (id int, content text);
CREATE TABLE
gaussdb=#  \d+ test_toast
                       Table "public.test_toast"
 Column  |  Type   | Modifiers | Storage  | Stats target | Description
---------+---------+-----------+----------+--------------+-------------
 id      | integer |           | plain    |              |
 content | text    |           | extended |              |
Has OIDs: no
Distribute By: HASH(a)
Location Nodes: ALL DATANODES
Options: orientation=row, compression=no, storage_type=USTORE, segment=off, toast.storage_type=USTORE, toast.toast_storage_type=toast
gaussdb=#  VACUUM FULL test_toast;
VACUUM
gaussdb=#  \d+ test_toast
                       Table "public.test_toast"
 Column  |  Type   | Modifiers | Storage  | Stats target | Description
---------+---------+-----------+----------+--------------+-------------
 id      | integer |           | plain    |              |
 content | text    |           | extended |              |
Has OIDs: no
Distribute By: HASH(a)
Location Nodes: ALL DATANODES
Options: orientation=row, compression=no, storage_type=USTORE, segment=off, toast.storage_type=USTORE, toast.toast_storage_type=enhanced_toast
gaussdb=#  DROP TABLE test_toast;
DROP TABLE
```
**分区表merge操作**
支持将分区表的分区间不同的线外存储表类型进行合并操作。
![](https://support.huaweicloud.com/distributed-devg-v10-gaussdb/public_sys-resources/note_3.0-zh-cn.png)
- 对于相同类型的线外存储分区，合并与原有逻辑保持一致，进行物理合并。
- 对于不同类型的线外存储分区，合并后的分区线外存储表为Enhanced Toast表，需要进行逻辑合并，性能劣于物理合并。
 
```
gaussdb=#  CREATE TABLE test_partition_table(a int, b text)PARTITION BY range(a)(partition p1 values less than (2000),partition p2 values less than (3000));
gaussdb=# SELECT relfilenode FROM pg_partition WHERE relname='p1';
 relfilenode
-------------
      17529
(1 row)
gaussdb=#  \d+ pg_toast.pg_toast_part_17529
TOAST table "pg_toast.pg_toast_part_17529"
   Column   |  Type   | Storage
------------+---------+---------
 chunk_id   | oid     | plain
 chunk_seq  | integer | plain
 chunk_data | bytea   | plain
Options: storage_type=ustore, toast_storage_type=toast
gaussdb=# SELECT relfilenode FROM pg_partition WHERE relname='p2';
 relfilenode
-------------
      17528
(1 row)
gaussdb=#  \d+ pg_toast.pg_toast_part_17528
TOAST table "pg_toast.pg_toast_part_17528"
   Column   |  Type   | Storage
------------+---------+---------
 chunk_seq  | integer | plain
 next_chunk | tid     | plain
 chunk_data | bytea   | plain
Options: storage_type=ustore, toast_storage_type=enhanced_toast
gaussdb=#  ALTER TABLE test_partition_table MERGE PARTITIONS p1,p2 INTO partition p1_p2;
ALTER TABLE
gaussdb=#  SELECT reltoastrelid::regclass FROM pg_partition where relname='p1_p2';
        reltoastrelid
------------------------------
 pg_toast.pg_toast_part_17559
(1 row)
gaussdb=#  \d+ pg_toast.pg_toast_part_17559
TOAST table "pg_toast.pg_toast_part_17559"
   Column   |  Type   | Storage
------------+---------+---------
 chunk_seq  | integer | plain
 next_chunk | tid     | plain
 chunk_data | bytea   | plain
Options: storage_type=ustore, toast_storage_type=enhanced_toast
gaussdb=# DROP TABLE test_partition_table;
DROP TABLE
```