DML

HTAP由实时事务单元TMU记录DML操作带来的增量数据变更，并维护IMCV列查询时的数据新鲜度，保证与行存实时数据的一致性。

示例：

gaussdb=# CREATE TABLE htap_test(
          id int,
          dept_id int,
          salary int,
          name varchar(20),
          comments varchar(30)) with (storage_type = ustore);
CREATE TABLE
gaussdb=# INSERT INTO htap_test VALUES (1, 1, 2000, 'Allen', 'for test');
INSERT 0 1
gaussdb=# INSERT INTO htap_test VALUES (2, 2, 3000, 'Lily', 'for test');
INSERT 0 1
gaussdb=# INSERT INTO htap_test VALUES (3, 2, 4000, 'Ann', 'for test');
INSERT 0 1

--加载IMCV。
gaussdb=# ALTER TABLE htap_test COLVIEW;
ALTER TABLE
gaussdb=# SELECT * FROM gs_imcv;
 reloid |  relname  | dbname | username | parentoid | imcvispart | imcvnattr |  imcvkey  | priority
--------+-----------+--------+----------+-----------+------------+-----------+-----------+----------
  17949 | htap_test | test   | dbdev    |         0 | f          |         5 | 1 2 3 4 5 |        1
(1 row)

--向表中插入新数据。
gaussdb=# INSERT INTO htap_test VALUES (4, 2, 3000, 'Bob', 'for test');
INSERT 0 1
--生成并选择执行IMCV执行计划。
gaussdb=# EXPLAIN SELECT /*+imcvscan(htap_test)*/  * FROM htap_test;
                              QUERY PLAN
----------------------------------------------------------------------
 Row Adapter  (cost=30.56..30.56 rows=459 width=148)
   ->  Imcv Scan on htap_test  (cost=30.00..30.56 rows=459 width=148)
(2 rows)
--获取IMCV查询结果，与行存数据一致。
gaussdb=# SELECT /*+imcvscan(htap_test)*/  * FROM htap_test;
 id | dept_id | salary | name  | comments
----+---------+--------+-------+----------
  1 |       1 |   2000 | Allen | for test
  2 |       2 |   3000 | Lily  | for test
  3 |       2 |   4000 | Ann   | for test
  4 |       2 |   3000 | Bob   | for test
(4 rows)

gaussdb=# DROP TABLE htap_test;
DROP TABLE