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Wang , Deng Ke 166ff0f192 rds usermanual 20230112 version for review 
Reviewed-by: Boka, Ladislav <ladislav.boka@t-systems.com>
Co-authored-by: Wang , Deng Ke <wangdengke2@huawei.com>
Co-committed-by: Wang , Deng Ke <wangdengke2@huawei.com>
2023-10-17 05:08:37 +00:00

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Rules for Distributing Weights

This section describes the rules of distributing read weights to DB instances of different specifications.

Weight Distribution Rules

When the system automatically sets the read weights for DB instances, the weight values are fixed.

The default weight equals to the number of vCPUs multiplied by 50. The weight ranges from 100 to 1000.

Adding a Hint to Specify the Direction that a SQL Statement Will Be Routed

Hints supported by read/write splitting are as follows:

  • /*FORCE_MASTER*/: A SQL statement is routed to the primary DB instance.
  • /*FORCE_SLAVE*/: A SQL statement is routed to a read replica.
  • In addition to the weight distribution system of read/write splitting, hints are a useful type of SQL syntax that allows you to specify whether a SQL statement is executed on the primary DB instance or on a read replica.
  • Hints are only used as routing suggestions. In non-read-only SQL and non-transaction scenarios, SQL statements cannot be routed to read replicas.