incremental shipping for standby databases

Hi,

I am getting the following message in my ADDM report.Can anyone tell me what does this mean?What is incremental shipping?

Finding 3: Log File Switches
Impact is .04 active sessions, 3.26% of total activity.
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Log file switch operations were consuming significant database time while
waiting for checkpoint completion.
This problem can be caused by use of hot backup mode on tablespaces.  DML to tablespaces in hot backup mode causes generation of additional redo.

   Recommendation 1: Database Configuration
   Estimated benefit is .04 active sessions, 3.26% of total activity.
   ------------------------------------------------------------------
   Action
      Verify whether incremental shipping was used for standby databases.

Thanks.