Informix

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  • 1.  AWS Snapshot and Informix IDS

    Posted Thu June 23, 2022 03:13 AM
    We have a client that has just migrated their live Informix IDS 14.10 instance into AWS and they have automated the process of taking a snapshot using AWS API on this Linux server.

    We have provided them with scripts to block and unblock transactions but I have a query regarding where and when the unblocking should take place. According to the documentation they have the unblocking can take place as soon as confirmation that the snapshot has started. I am not 100% up to speed on AWS snapshots but should the unblocking only be performed once the snapshot has completed?

    Thanks.

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    Greg Bunting
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    #Informix


  • 2.  RE: AWS Snapshot and Informix IDS

    IBM Champion
    Posted Thu June 23, 2022 04:17 AM
    Greg:

    Not a big fan of snapshots for backing up Informix chunks, so, as a naturally paranoid DBA, I would wait until the snapshot has completed. Maybe someone from HCL can give a more informed answer though.

    Art

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    Art S. Kagel, President and Principal Consultant
    ASK Database Management Corp.
    www.askdbmgt.com
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    Original Message


  • 3.  RE: AWS Snapshot and Informix IDS

    Posted Thu June 23, 2022 04:55 AM
    Thanks for the response Art - you have basically confirmed my view.

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    Greg Bunting
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    Original Message


  • 4.  RE: AWS Snapshot and Informix IDS

    Posted Thu June 23, 2022 10:28 AM

    I would say same as Art: I am not a big fan either of snapshots: the problem is that a snapshot is just a physical image of your chunks, and you have absolutely no control on what happens with your transactions + you'll have to forget about logical logs recovery (meaning if you are unlucky, you may lose a full day of activity if you have to restore a few minutes before the snaphot time...) Snapshots are far away from what a reasonable DBA has in mind, and forget about logical logs recovery.

     

    And yes, provided that AWS has no clue of what your transactions do, I would wait for the end of the snapshot before running the onmode -c unblock command.

     

    Many times, virtualization specialists sell you marvellous functionality such as snapshots, but at the end, you end with less control than what the Informix backup (onbar) will give you...Some call it progress, I don't

    (unless there is something I did not understand about VM snapshots...)

     

    Thanks

    Eric

    Eric Vercelletto
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    Original Message


  • 5.  RE: AWS Snapshot and Informix IDS

    IBM Champion
    Posted Thu June 23, 2022 10:35 AM
    Edited by System Fri January 20, 2023 04:31 PM
    I'd say if such snapshot is done, for at least all Informix chunks at a time, in a way that all writes occurring while the snapshot is progressing won't make it into the snapshot, then it would be ok to lift the Informix block right after the snapshot started.
    Only a snapshot behaving this way should be deserving this name ;-)

    This is what needs to be figured out - would be interesting to learn here.

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    Andreas Legner
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    Original Message


  • 6.  RE: AWS Snapshot and Informix IDS

    IBM Champion
    Posted Thu June 23, 2022 10:42 AM

    Also depends where the snapshot is taken, using ZeroTo the snap is taken at the hardware level and disk writes are blocked at the hardware level, i.e. below the VM

     

    Cheers

    Paul

     




    Original Message


  • 7.  RE: AWS Snapshot and Informix IDS

    Posted Fri June 24, 2022 06:40 AM
    From Greg's original description, I'm not sure whether he refers to "snapshots" as what is called "Amazon EBS snapshot" on this page: https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ebs-creating-snapshot.html .

    If this is what Greg is asking about, then I think the Informix blocking can be released as soon as the snapshot start is confirmed.

    My rationals for this are:
    When the Informix "onmode -c block" returns the prompt, it is assured that the Informix server has finished writing to the disks, i.e. disk content must be physically consistent. At this point, the snapshot can be started.

    A common technique for doing snapshots is that disks/volumes are mirrored. The start of the snapshot detaches the mirrored disk/volume. As at this point there's no writing activity as guaranteed by the Informix checkpoint block, the now detached mirror contains the physically consistent data, which now can't receive any more modifications (it's detached). The write activity on the primary disk/volume of the mirror pair now can resume (without affecting the detached mirror). At this point, the Informix checkpoint block can be lifted ("onmode -c unblock"). The detach operation should take very little time. While Informix work now can continue, the data from the detached mirror gets backed up to a safe place (seemingly "Amazon S3", whatever that means). Once this backup is done, the mirror disk/volume gets re-attached to the primary disk/volume and synced with the data that has changed since the detaching. Once the syncing is done, it should then be possible to repeat the whole procedure for the next snapshot.

    Please carefully read the Amazon documentation of the snapshot, especially what on above mentioned page is described as "incremental". This may be handled automatically by "Amazon S3" ... but I guess, you want to be sure that it does what you think it is doing.

    As mentioned before by others in this thread, handling of logical logs and their backup is not included in such snapshots.

    Regards, Martin

    --

    Martin Fuerderer

    Software Engineer, Software Development

    HCL Technologies Ltd.

    Frankfurter Ring 17

    80807 Munich, Germany

    www.hcltechsw.com


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