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Oracle: LGWR wait on LNS


Good discussion on LGWR LNS waits at:


here is a snipit:
    • Hello Kay

      From your statspack, I think, you are correct. Even though LGWR ASYNC mode prevents primary from encountering ‘log file sync’ waits due to network latency, it doesn’t necessarily prevent when LGWRLNS communication and messaging has latencies. In your case, your statspack output indicates that you may be running in to issues with LNS buffer flushing or LNS communication not completing quick enough. I guess, truss or dtrace of LGWR will confirm this.

      I guess, LNS process tuning is in order to resolve this intermittent issue. Of course, network latency is another area to look at.

      Cheers
      Riyaj

      Comment by orainternals — February 24, 2009 @ 6:51 pm Reply

  1. Thanks.. LGWR-LNS communication and messaging latency is a more accurate way of putting it. In our case, this latency happened to be caused by network. Noted your point that there could be other reasons that slow down LNS too. Thanks for your help.

    Comment by Kay Guo — February 24, 2009 @ 9:00 pm Reply


From the docs
10.3.5.3 LGWR ASYNC Wait Events

The following wait events are for standby destinations configured with the log writer (LGWR) ASYNC attributes:

  • LNS wait on ATTACH: This wait event monitors the amount of time spent by all network servers to spawn an RFS connection.

  • LNS wait on SENDREQ: This wait event monitors the amount of time spent by all network servers to write the received redo to disk as well as open and close the remote archived redo log files.

  • LNS wait on DETACH: This wait event monitors the amount of time spent by all network servers to delete an RFS connection.

  • LGWR wait on full LNS buffer: This wait event monitors the amount of time spent by the LGWR process waiting for the network server (LNS) to free up ASYNC buffer space. If buffer space has not been freed in a reasonable amount of time, availability of the primary database is not compromised by allowing the archiver process (ARCn) to transmit the redo log data. This wait event is not relevant for destinations configured with the LGWR SYNC=PARALLEL attributes.


    Note:

    This wait event is not relevant for destinations configured with the LGWR SYNC=NOPARALLEL attributes.

10.3.5.4 LGWR ASYNC or LGWR SYNC=PARALLEL Wait Events

The following wait events are for standby destinations configured with either the log writer (LGWR) ASYNC or LGWR SYNC=PARALLEL attributes:

  • LGWR wait on LNS: This wait event monitors the amount of time spent by the LGWRprocess waiting to receive messages on IPC channels from the network server.

  • LNS wait on LGWR: This wait event monitors the amount of time spent by the network server waiting to receive messages on IPC channels from the LGWR process.

  • LGWR-LNS wait on channel: This wait event monitors the amount of time spent by the LGWR process or the network server processes waiting to receive messages on IPC channels.

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