AnalyticDB for PostgreSQL:Change compute node configurations

Add compute nodes

The elastic scaling feature ensures that your business runs normally and data reads and writes are uninterrupted on all tables in the database when you change compute node configurations. When you add compute nodes to an AnalyticDB for PostgreSQL V6.0 instance in elastic storage mode whose minor version is 6.6.2.0 or later or an AnalyticDB for PostgreSQL V7.0 instance in elastic storage mode whose minor version is 7.0.5.0 or later, the elastic scaling feature is supported. Take note of the following items:

• When you change compute node configurations, data redistribution is performed on all tables in sequence. Tables not in the redistributing state are not affected. Tables in the redistributing state support all query operations and the INSERT, COPY, DELETE, and UPDATE statements, but do not support DDL statements and VACUUM statements. When you execute a DDL statement such as TRUNCATE TABLE, an error is returned, as shown in the following code:

TRUNCATE t1;
ERROR:  Unsupport 'TRUNCATE TABLE' command during online expansion on 't1'

• If a large amount of data is written or updated, an extended period of time is required to change compute node configurations. If data is frequently written to specific tables, a write lock is added to the tables to speed up the change of compute node configurations. When you add compute nodes to an AnalyticDB for PostgreSQL instance in elastic storage mode that supports the elastic scaling feature, you can view the scaling progress in the AnalyticDB for PostgreSQL console.

1. Log on to the AnalyticDB for PostgreSQL console.
2. In the upper-left corner of the console, select a region.

3. Find the instance that you want to manage and choose Change Compute Node Configurations > Add Compute Node in the Actions column.

4. In the Info dialog box, select I am aware of the impact of this operation and agree to continue it. and click OK.

   Note

   This step is available only for instances in Serverless mode.

5. On the Upgrade/Downgrade page, select a value for the Nodes parameter based on your business requirements, read and select the Terms of Service, and then click Buy Now.

   Warning

   • For an AnalyticDB for PostgreSQL V6.0 instance in elastic storage mode whose minor version is earlier than 6.6.2.0 or an AnalyticDB for PostgreSQL V7.0 instance in elastic storage mode whose minor version is earlier than 7.0.5.0, tables that are in the redistributing state can only be read when you change the number of compute nodes. For an AnalyticDB for PostgreSQL V6.0 instance in elastic storage mode whose minor version is 6.6.2.0 or later or an AnalyticDB for PostgreSQL V7.0 instance in elastic storage mode whose minor version is 7.0.5.0 or later, tables that are in the redistributing state can be both read and written when you change the number of compute nodes. The amount of time that is required to redistribute data varies based on the table size. Perform this operation during an appropriate period of time.

   • For instances in Serverless mode, after you submit a request to change the number of compute nodes, the current SQL statements are interrupted. These SQL statements cannot be resumed even after the change.

6. Return to the Instances page and wait for the instance to enter the Running state.

7. You can execute the following SQL statement to prefetch data from tables that have high performance requirements to accelerate data access.

   SELECT count(*) FROM <hot_table>;

   Note

   • Data prefetching is required only for instances in Serverless mode.

   • When you change the number of compute nodes, the following operations are performed: The resources are initialized, the metadata about system tables is synchronized, the resources are locked to modify the data distribution information, the resources are unlocked and cleared, and the local cache is asynchronously restored. The hit ratio of the local cache remains low for a short period of time because the local cache is asynchronously restored. You can prefetch data to accelerate data access.

Remove compute nodes

1. Log on to the AnalyticDB for PostgreSQL console.
2. In the upper-left corner of the console, select a region.

3. Find the instance that you want to manage and choose Change Compute Node Configurations > Remove Compute Node in the Actions column.

4. In the Info dialog box, select I am aware of the impact of this operation and agree to continue it. and click OK.

5. On the Upgrade/Downgrade page, select a value for the Nodes parameter based on your business requirements, read and select the Terms of Service, and then click Buy Now.

   Warning

   • For instances in elastic storage mode, tables that are in the redistributing state can only be read when you change the number of compute nodes. The amount of time that is required to redistribute data varies based on the table size. Perform this operation during an appropriate period of time.

   • For instances in Serverless mode, after you submit a request to change the number of compute nodes, the current SQL statements are interrupted. These SQL statements cannot be resumed even after the change.

6. Return to the Instances page and wait for the instance to enter the Running state.

7. You can execute the following SQL statement to prefetch data from tables that have high performance requirements to accelerate data access.

Upgrade node specifications

1. Log on to the AnalyticDB for PostgreSQL console.
2. In the upper-left corner of the console, select a region.

3. Find the instance that you want to manage and choose Change Compute Node Configurations > Upgrade Node Specifications in the Actions column.

4. On the Upgrade/Downgrade page, configure the parameters. The following table describes the parameters.

   Parameter	Description
   Instance Resource Type	The resource type of the current instance is displayed and cannot be modified.
   Compute Node Specifications	Select node specifications based on your business requirements.
   Single Node Storage Capacity	Select a storage capacity per node based on your business requirements.

   Warning

   • Data can only be read when you change the node specifications. Perform this operation during an appropriate period of time.

   • Data reads and writes are not affected when you change the storage capacity.

5. Read and select the Terms of Service, and then click Buy Now.

6. Return to the Instances page and wait for the instance to enter the Running state.

Downgrade node specifications

1. Log on to the AnalyticDB for PostgreSQL console.
2. In the upper-left corner of the console, select a region.

3. Find the instance that you want to manage and choose Change Compute Node Configurations > Downgrade Node Specifications in the Actions column.

4. On the Downgrade page, configure the parameters. The following table describes the parameters.

   Parameter	Description
   Instance Resource Type	The resource type of the current instance is displayed and cannot be modified.
   Compute Node Specifications	Select node specifications based on your business requirements.
   Single Node Storage Capacity	The storage capacity per node cannot be downgraded. Note This parameter is unavailable for Basic Edition instances in elastic storage mode.

   Warning

   • Data can only be read when you change the node specifications. Perform this operation during an appropriate period of time.

   • Data reads and writes are not affected when you change the storage capacity.

5. Read and select the Terms of Service, and then click Buy Now.

6. Return to the Instances page and wait for the instance to enter the Running state.