Introduction to the implementation principle of distributed database Middleware four: smooth expansion

Disclaimer: This article is not original and is a product introduction to distributed Database Middleware (DDM) services from Huawei Cloud Help Center.

with the growth of the business, the logical library storage space is not enough, the concurrency pressure is large, at this time the DDM instance logical library can be scaled up, by increasing the RDS instance to improve the data storage capacity and concurrency support capability.

Smooth expansion is a way of horizontal expansion, by increasing the number of RDS instances to increase the overall data storage capacity, the sub-database is smoothly expanded to the new RDS instance, to ensure that all the data are distributed evenly on each sub-library, reducing the processing pressure of a single RDS instance.

The following restrictions apply to smooth expansion:

• The RDS instance and the DDM instance need to be in the same VPC, and the RDS instance is not used by other DDM instances.
• A table must be available under the logical library for smooth scaling.
• An instance cannot be expanded without a node failure.
• In an DDM instance, only one instance logical library is allowed to be scaled smoothly, and the instance logical library can be expanded at the same time in different DDM instances.
• The use of RDS instances in the expansion is not allowed to build the database table operation.
• Only up to 50 RDS instances are supported for expansion.
• The maximum size of the expansion is:
  • No more than 20 tables per shard.
  • No more than 8 million data per table.

The principle of smoothing expansion is shown in 7.

Figure 7 Principle of smooth expansion

Introduction to the implementation principle of distributed database Middleware four: smooth expansion