Proxy object is used to create a binding between incoming connections from the database clients to the database servers. Each incoming connection will connect to the server. Upon connection, the server object instructs the proxy object to assign an available client object from the pool. If no client object is available, the proxy object will reject the incoming connection with an error.

If any traffic comes from the incoming connection, it will be forwarded to the server. It will wait for the server to respond and forward the response back to the incoming connection. The proxy object will also handle the connection health check and the connection timeout.

Proxy object

The following sequence diagram shows how the proxy object works.

    database client->>+server: connect
    server->>proxy: connect
    proxy->>available pool: give me a free connection
    available pool->>proxy: here is a free connection
    proxy->>busy pool: assign connections
    busy pool->>proxy: done
    proxy->>server: done
    server->>database client: ready

Both the available pool and the busy pool are created and managed by the proxy object.

Traffic handling

The following sequence diagram shows how the proxy object handles the traffic.

    database client->>+server: query
    server->>proxy: there is traffic from database client
    proxy->>busy pool: give me the connected client
    busy pool->>proxy: here is the connected client
    proxy->>connected client: send query to database
    connected client->>database: send query
    database->>connected client: receive response
    connected client->>proxy: here is the response from database
    proxy->>server: send response to database client
    server->>database client: response

Connection health check

The proxy object will periodically check the connection health by disconnecting stale connections the database server and creating the same number of new connections to the database server. The following sequence diagram shows how the proxy object handles the connection health check. Stale connections are connections that have not been used for a long time and are considered unhealthy.

    proxy health check->>available pool: Are there any available clients?
    available pool->>proxy health check: Yes
    proxy health check->>clients: Terminate the client(s)
    proxy health check->>available pool: Remove the client
    proxy health check->>clients: Create new client(s)
    clients->>proxy health check: Here are the new client(s)
    proxy health check->>available pool: Store the connections