process update - dropping bitmap indexes RRS feed

  • Question

  • Hi,<o:p></o:p>

    Process Update of my dimensions is beginning to take a very long time. Looking in the
    profiler we see events that the measure group partitions are processing. From
    my understanding this is because bitmap indexed on the partitions are being
    dropped because dimension members were either changed or deleted (if the
    dimension have flexible relationships, which mine do). Then you have the option
    to process affected objects (recreating these indexes automatically) or you can do a process
    index yourself.<o:p></o:p>

    Ok, but if you choose to do none of these, then why the next day we process the cube do we
    see the same thing during the process update of the dimensions? The previous
    day the bitmap indexes were dropped and not recreated, so how can they be
    dropped again?<o:p></o:p>

    This part of the process update is takings at least 90% of the full process update operation.<o:p></o:p>

    Any help on this would be great.<o:p></o:p>


    Thursday, January 22, 2015 8:51 AM

All replies

  • Hi kiwiNspain,

    According to your description, you find when you do Prcess Update, the bitmap indexes are dropped. Right?

    In Analysis Services, ProcessUpdate can affect dependent partitions depending on the nature of the changes in the dimension table. If only new members were added, then the partitions are not affected. But if members were deleted or if member relationships changed (e.g., a Customer moved from Redmond to Seattle), then some of the aggregation data and bitmap indexes on the partitions are dropped. The cube is still available for queries, albeit with lower performance.(with ProcessUpdate Flexible aggregations and indexes on related partitions will be dropped). Otherwise it should not change the bitmap indexes, can you share some information about what you have done in the update. It may help us figure out the root cause.

    Different Kinds of SSAS Processing in simple words…..

    Simon Hou
    TechNet Community Support

    Sunday, January 25, 2015 3:37 PM
  • Hi Simon,

    The update of the dimension is either updates of attributes or new rows added, no deletes. The dimension has 300+ attributes.

    The behavious I tested is as follows:

    1. Process Full Dims and Measure groups
    2. ETL to update the dimension
    3. ProcessUpdate dimension with process affected objects disabled. In the profiler I see process partition events (dropping bitmap indexes).
    4. ETL to update dimension again
    5. ProcessUpdate dimension with process affected objects disabled. Again in the profiler I see the same process partition events

    The step I don't understand is step 5. You can see I didn't process any cube partition after step 3, so the bitmap indexes wouldn't have been created again.

    Monday, January 26, 2015 1:47 PM