Matches when the calculated layout has already been logged. Useful if having an aggressive logger, and wants to throttle the output.

Introduced with NLog ver. 4.5

<rules>
  <logger ... >
    <filters defaultAction="Log">
      <whenRepeated layout="Layout" timeoutSeconds="30" action="Ignore" />
    </filters>
  </logger>
</rules>

Can also be combined with FilteringWrapper-target.

• layout - Layout to be used to filter log messages. Layout Required.
• timeoutSeconds - How long to ignore identical messages before logging again (Default 10 secs)
• action - Action to be taken when filter matches. Required.
  Possible values:
  • Ignore - The message should not be logged.
  • IgnoreFinal - The message should not be logged and processing should be finished.
  • Log - The message should be logged.
  • LogFinal - The message should be logged and processing should be finished.
  • Neutral - The filter doesn't want to decide whether to log or discard the message.
• includeFirst - Should action also be applied to the initial logevent? When enabled then it will only perform the first logging if the messages continues after the initial timeout. (Default: false)

• FilterCountPropertyName - Tell how many identical log messages has been ignored. By adding LogEvent-Property with this name to the next LogEvent after timeout expires.
• FilterCountMessageAppendFormat - Tell how many identical log messages has been ignored. By appending to LogEVent-Message to the next LogEvent after timeout expires (Ex. " (Hits: {0}")

• MaxLength - Max number of characters to include when checking for identical messages (Default 1000 characters)
• MaxFilterCacheSize - Max number of unique log messages to keep in cache, before starting to prune (Default 50000)
• DefaultFilterCacheSize - Initial start size of the cache for keep track of unique log messages (Default 1000)
• OptimizeBufferDefaultLength - Initial allocated size of the reusable buffers (Default 1000)