What job runs AWR snapshot? Eh?

There are a surprising number of online resources propagating the idea that the collecting of AWR snapshots is somehow connected to the GATHER_STATS_JOB (which was responsible for automatically gathering stats in 10g).

Eh?

Collecting AWR snapshots is one of the responsibilities of the background process MMON.

If you have a problem with the automatic snapshots:
– Check whether you can manually snap using DBMS_WORKLOAD_REPOSITORY.CREATE_SNAPSHOT.
– Check MMON and alert log / trace files for related messages.
– See Metalink note 1301503.1: “Troubleshooting: AWR Snapshot Collection issues”

This came up in a question on the OTN forums where the OP said that AWR was not snapping automatically but the GATHER_STATS_JOB seemed to be ok. And the obvious first question would be where did you get that idea from?
Sometimes you can’t win on the forums. If you ask a question, it’s not uncommon to be pointed to a google search. But if you google something, you can’t trust everything that’s out there – it gets outdated and sometimes it never was accurate.

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5 Responses to What job runs AWR snapshot? Eh?

  1. jgarry says:

    From the XE 11g MMON trace file, on a minimal system, barely used:

    —————————————————
    The sampled session history is constructed by sampling
    the target session every 1 second. The sampling process
    captures at each sample if the session is in a non-idle wait,
    an idle wait, or not in a wait. If the session is in a
    non-idle wait then one interval is shown for all the samples
    the session was in the same non-idle wait. If the
    session is in an idle wait or not in a wait for
    consecutive samples then one interval is shown for all
    the consecutive samples. Though we display these consecutive
    samples in a single interval the session may NOT be continuously
    idle or not in a wait (the sampling process does not know).

    The history is displayed in reverse chronological order.

    sample interval: 1 sec, max history 120 sec
    —————————————————
    —– END DDE Action: ‘ORA_12751_DUMP’ (SUCCESS, 2 csec) —–
    —– END DDE Actions Dump (total 2 csec) —–
    *** KEWRAFM1: Error=12751 encountered by Auto Flush Main.
    KEBM: MMON action policy violation. ‘AWR Auto Flush Task’ viol=1; err=12751

    Thus, Schrödinger’s cat is killed, in no uncertain terms, as an error says to call Oracle support, for a product that is not supported, with an option that cannot be licensed or used.

    Note 761298.1: “If the load on the system is extremely high, this is expected, and error can be ignored.”

    A little more difficult to ignore when the load is extremely low and the system locks up. I hope that is not expected.

    • Dom Brooks says:

      > Schrödinger’s cat
      I had to do a search for this term to find out what you were talking about. I read something at wikipedia or somewhere similar and to be honest it went a little over of head.

      Then it cropped up again in the paper just the other day, here:

      http://www.telegraph.co.uk/science/science-news/8875967/Testing-the-Copenhagen-interpretation-a-matter-of-live-and-dead-cats.html

      So I read that article touching on quantum theory and GRWP and I thought of two contrasting things which are relevant to any sort of investigation including performance.

      The first is that just because you can come up with a theory that explains everything, doesn’t mean it’s true. That was my main reaction to what I was reading.

      And the other is from Sherlock Holmes – “when you have eliminated the impossible, whatever remains, however improbable, must be the truth”.

  2. Graham says:

    I was left completely dumbfounded when I told a developer at work that we had no AWR history and he replied by saying that he’d just run dbms_stats. Strange how that seems to have got around.

  3. Stunned. What is there to confuse? I could understand people confusing ASSM ASMM, and even ASM on at least an acronym level. I suppose it is because there is no obvious mechanism (scheduled task) for the scheduled collection (What? The background processes actually do stuff?).

  4. GASCARD.T says:

    It seems this bad information is an Oracle Press Book “Oracle Tuning 10gR2″ by Richard Niemec.So be careful with books too..

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