Data Management:Lock-free schema changes

Procedure

In this example, the lock-free schema change feature is used to change the data type of the long_text_a column in the big_table table of the poc_dev database in Security Collaboration mode from varchar(1024) to text.

1. Submit a ticket as a regular user.

   1. Log on to the DMS console V5.0 as a regular user.

   2. In the top navigation bar, choose Database Development > Data Change > Lockless Change.

      Note

      If you are using the DMS console in simple mode, move the pointer over the icon in the upper-left corner of the console and choose All functions > Database Development > Data Change > Lockless Change.

   3. Set the parameters that are described in the following table and click Submit.

      Parameter	Description
      Database (Required)	Required. The database in which you want to change data. In this example, the poc_dev database in Secure Collaboration mode is selected.
      Business Background (Required)	Required. The purpose or objective of the data change. This reduces unnecessary communication.
      Affected Rows (Required)	Required. The estimated number of data rows that will be affected by the data deletion operation. To obtain the actual number of affected rows, you can use the COUNT function in SQL statements and execute the SQL statements on the SQLConsole tab.
      SQL Statements for Change (Required)	Required. The SQL statement that you want to execute to change data. In this example, the following ALTER statement is executed: ALTER TABLE `big_table` MODIFY COLUMN `long_text_a` text NULL AFTER `name`; Note This statement changes the data type of the long_text_a column from varchar(1024) to text.

   4. On the Ticket Details page, confirm the ticket details.

      Note

      You can view the ticket details on the Ticket Details page. DMS prechecks the SQL statement that you want to execute. The precheck items include the syntax of the SQL statement, whether the type of the SQL statement matches the type that you configured in the security rules, the permissions of the user who submitted the ticket, and the estimated number of rows to be scanned.

   5. After the ticket details are confirmed and the precheck is complete, click Submit for Approval. In the message that appears, click OK.

      Important

      You can modify the ticket details only before you submit the ticket for approval.

2. Approve the ticket as a DMS administrator.

   1. Log on to DMS console V5.0 as a DMS administrator.

   2. On the Home page of the DMS console, click Pending Tickets in the My Tickets section.

   3. On the My Tickets page, find the ticket that you want to handle and click the ticket number in the Ticket Number column.

   4. In the Ticket Details panel, confirm the data change information in the ticket and click Approve.

   5. In the dialog box that appears, enter comments and click Submit.

3. Execute the ticket as a regular user.

   1. Log on to the DMS console V5.0 as a regular user.

   2. In the Execute section in the Ticket Details panel, click Execute Change. In the dialog box that appears, set the parameters that are described in the following table and click Confirm Execution.

      Parameter	Description
      Execute strategy	Specifies whether to execute the task immediately or at a scheduled time. Valid values: Running immediately: DMS runs the task immediately after you submit the task. Schedule: DMS runs the task at the scheduled time that you specify. Default value: Running immediately.
      Transaction Control	Specifies whether to enable transaction control. Valid values: on: If an SQL statement fails to be executed, all the executed DML statements in the same transaction are rolled back. DDL statements cannot be rolled back. off: One SQL statement is executed at a time. If an SQL statement fails to be executed, the transaction is stopped. The other executed SQL statements in the same transaction are not rolled back. Default value: off.
      Data Backup	Specifies whether to back up data. Valid values: on: DMS generates INSERT scripts to back up the data that will be affected when UPDATE or DELETE statements are executed. off: No backup scripts are generated for the preceding data. Default value: on.

      Note

      After you click Confirm Execution, DMS starts to run the task.

View the task progress and verify the schema

1. Move the pointer over the name of the database to be changed in the Basic Information section as a DMS administrator. In the menu that appears, click Query.

   You are automatically redirected to the page of SQL Console.

2. On the SQL Console tab, enter an SQL query statement in the SQL editor. Then, click Execute in the upper part of the SQL editor.

   For example, you can enter the following SQL statement to query the tables of the current database.

   SHOW TABLES;

   Note

   When DMS changes the schema of a table without locking tables, two temporary tables are generated.

3. In the top navigation bar, choose O&M > Task.

   Note

   If you use the DMS console in simple mode, move the pointer over the icon in the upper-left corner of the DMS console and choose All Features > O&M > Task.

4. Click the task number of the task that you want to manage. The Execution details dialog box appears.

5. Click Progress in the Operation column.

6. In the Lock-Free structure change message, view the progress information of the task.

7. After the task is complete, verify the schema.

   The schema of the big_table table is changed, and the temporary tables are deleted.