The Search Server incorporates session pooling for all searches. Session pooling eliminates Rulebase access when a client switches between searches within the same session or when a new client connects. Session pooling improves search performance and eliminates the need for the clients to implement the session pooling logic within their own application code.
By default, session pooling is enabled. You can disable it by setting the SSA_SESSION_POOL_MAX environment variable to 0 on the machine hosting the Search Server.