parameter "vacuum_defer_cleanup_age"

Hi,

    I have 2 servers, working with Hot-Standby and Streaming
    Replication...
    and when we executed some query much large returns a message..
    "canceling statement due to statement
      timeout"
      I want know, how can I calculate the better value to
      "vacuum_defer_cleanup_age" in my case?

      Tell me if you recommend changes in other parameter.

      Thanks

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