code: ServerSessionContext setKeepAliveIndex(long keepAliveIndex) {
      long previousKeepAliveIndex = this.keepAliveIndex;
      this.keepAliveIndex = keepAliveIndex;
      if (previousKeepAliveIndex > 0) {
        log.release(previousKeepAliveIndex);
      }
      return this;
    }
docs: Sets the current session keep alive index.
  
  @param keepAliveIndex The current session keep alive index.
  @return The server session.