This topic describes how to verify the effect of read/write splitting for an ApsaraDB RDS for MySQL instance by executing the /*PROXY_INTERNAL*/show last route; statement, which is a hint. In this case, you must log on to the RDS instance by using the read/write splitting endpoint.

Note Currently, we recommend that you do not use this SQL statement in the production environment because it is still under internal testing and may be updated later.

View the RDS instance to which an SQL statement is sent


  1. Connect to an RDS instance by using its read/write splitting endpoint from your client. For more information, see Connect to an ApsaraDB RDS for MySQL instance.
  2. Execute the following statement to view the ID of the instance where the previous SQL statement is executed:
    /*PROXY_INTERNAL*/show last route;
    • You can execute this statement only when your application connects to the read/write splitting endpoint of the RDS instance.
    • If you use the mysql character terminal to connect to the RDS instance, you must include the -c parameter. Otherwise, the system ignores comments and reports the following error:
      ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that
      corresponds to your MySQL server version for the right syntax to use near 'last route' at
      line 1

View results

In the command output, last_bkid indicates the ID of the destination database for the previous SQL statement (the one above the hint). This type of ID uniquely identifies an RDS instance. The following figure shows further details.

Note RDS instances process SQL statements in bulk and each bulk includes 100 statements. For example, the first 100 SELECT statements are executed on the same instance and SELECT Statement 101 is sent to another instance. You can use the following a.sql file to verify this process:
select 1;
/*PROXY_INTERNAL*/show last route;select 1;
***100 executions***;
select 1;
/*PROXY_INTERNAL*/show last route;

The command output shows that SELECT Statement 101 is sent to another instance. (Assume that more than two read-only instances are available for the statements).

Verify that all write requests are sent to the primary instance

After the read/write splitting function is enabled for an RDS instance, write requests can only be sent to the primary instance because read-only instances can only process read requests. If a write request is sent to a read-only instance, the system re-sends the write request to the primary instance based on the error cause (read_only error).

Execute an INSERT statement and then execute the following statement to verify that the write request is sent to the primary instance:

/*PROXY_INTERNAL*/show last route;