The keep-alive is a facility where the proxy keeps the connection to the backend server - even if the client closes the connection to the proxy.
If a new or another client connects to the proxy again and requests the same backend it will be reassigned to this backend. In this case, the proxy sends an initialize response directly to the client and an initialize handshake with the backend is omitted.
When a client reconnects, query and record caching works better, if the proxy assigns it to the same backend as before. And the result set (if any) is re-used. To achieve this, Index Data defined a session cookie which identifies the backend session.
The cookie is defined by the client and is sent as part of the
Initialize Request and passed in an
element with OID
Clients that do not send a cookie as part of the initialize request may still better performance, since the init handshake is saved.
Refer to Section 9.7, “keepalive” on how to setup configuration parameters for keepalive.