What Is Database Proxy

Basic Concepts

• Proxy Address

  After purchasing a proxy instance, you can view the proxy address on the Database Proxy page. The proxy instance sends write requests to the primary node and read requests to read replicas through this address.

• Proxy Mode

  There are read/write and read-only proxy modes.

  Read/Write: All write requests are routed only to the primary node, and all read requests are routed to the selected nodes based on the read weights or active connections.

  Read-only: All read requests are routed to the selected read replicas based on the read weights or active connections. The read requests will not be routed to the primary node.

• Transaction Splitting

  With transaction splitting is enabled for a proxy instance, the proxy instance can route the read requests prior to write operations in a transaction to read replicas, reducing the pressure on the primary node.

  For more information about transaction splitting, see Enabling Transaction Splitting for a Proxy Instance.

• Connection Pool

  Proxy instances provide session-level connection pools, which help reduce the database load caused by frequent establishment of short connections.

  For more information about connection pools, see Enabling the Connection Pool for a Proxy Instance.

• Routing Policy

  Proxy instances support weighted and load balancing routing policies.

  • Weighted: Read requests are assigned to nodes based on the weights you specify.
  • Load balancing: Read requests are assigned to nodes with fewer active connections. In load balancing policy, you do not need to configure the weights of nodes.

  For more information about routing policies, see Modifying the Routing Policy for a Proxy Instance.

How Read/Write Splitting Works

You can create one or more proxy instances for your GaussDB(for MySQL) instance to enable read/write splitting.

• Single proxy instance

  If your GaussDB(for MySQL) instance has only one proxy instance, applications connect to the proxy instance through the proxy address. Write requests are forwarded to the primary node and read requests to the primary node or read replicas based on the routing policy you specify.

  Figure 1 Read/write splitting with only one proxy instance
  
• Multiple proxy instances

  To isolate workloads from different applications, you can create up to four proxy instances for your GaussDB(for MySQL) instance. Different applications can connect to different proxy instances as required. The associated nodes of the proxy instances process read requests from different applications for workload isolation.

  Figure 2 Read/write splitting with multiple proxy instances
  

Application Scenarios

• The primary node is overloaded due to a large number of requests in a transaction.
• The primary node is overloaded due to excessive connections.
• Read/write splitting is required.

Read/Write Splitting Advantages

• Compared with manual read/write splitting in applications, the read/write splitting using proxy addresses features flexible scale-out and low maintenance costs.
• Read requests are distributed to your read replicas based on weights to balance your database traffic and improve resource utilization.
• A proxy instance routes read requests of an application only to its associated read replicas to isolate workloads.
• By default, proxy instances provide overload protection to prevent server OOM (out of memory) due to heavy pressure when you perform operations on large result sets. This function is enabled by default and does not need to be configured separately. The pressure caused by the slow kernel depends on flow control.

Request Routing Rules

• Write requests sent only to the primary node
  • INSERT, UPDATE, and DELETE
  • All DDL operations (such as table/database creation, table/database deletion, table structure change, and permission change)
  • All requests in transactions (But if transaction splitting is enabled, some read requests in transactions may be sent to read replicas. For details, see Enabling Transaction Splitting for a Proxy Instance.)
  • User-defined functions
  • Stored procedures
  • EXECUTE statements
  • Multi-statement requests
  • Requests that use temporary tables
  • All changes to user variables
  • KILL in SQL statements (not command KILL)
• Read requests sent only to the primary node
  • If query statements are in transactions, the transaction requests are routed to the primary node. If SET AUTOCOMMIT=0 is added before a query statement, the transaction requests are routed to the primary node.
  • If all read replicas are abnormal or the read weights allocated to the read replicas are 0, requests will be routed to the primary node. You can set read weights for the primary node and read replicas after read/write splitting is enabled.
  • When running SQL statements:
    • If multi-statements (for example, insert xxx;select xxx) are executed, all subsequent requests will be routed to the primary node. To restore read/write splitting, disconnect your application from your instance and then connect it back again.
    • Read operations with locks (for example, SELECT for UPDATE) will be routed to the primary node.
    • When /*FORCE_MASTER*/ is used, requests will be routed to the primary node.
    • If the HANDLER statement is executed, all subsequent requests will be routed to the primary node by default. To restore read/write splitting, disconnect the connection and reestablish a connection.
  • SELECT last_insert_id()
  • All queries of user variables
• The following requests will be routed either to the primary node or a read replica.
  • SELECT not in a transaction
  • The COM_STMT_EXECUTE command
• The following requests will always be routed to all nodes.
  • Changes to all system variables
  • The USE command

Read/Write Attribute Processing Logic

There are read-only and read/write modes for proxy instances. The read/write attribute processing logic varies depending on the proxy mode.

Billing

Proxy instances are free of charge.

Precautions