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Cache in BIA

Can somebody explain how Cache works in BIA. We are on Rev 50.

In the Python tool, under Index -> Usage -> Cache.

Issue - when i run the query for the first time in BIA, it runs for about 5 secs on BIA. but when i run the same query again (with exactly the same variables) it returns in less than 1 sec (Note - OLAP Cache is disabled in both the cases).

Under Index -> Usage -> Cache, I can see Cache size increasing for a query run for the first time while i can see Cache Hits increasing for any subsequent runs.

If I change any variable from the previous run, it populates another entry in BIA Cache which takes pretty long time (5 secs or so). My question is that how is this different from OLAP cache. If i am going against exactly same data again (same query with same variables), wouldn't I hit OLAP cache (assuming that its hitting the same app server) and never hit BIA at all which makes BIA cache useless. What am I missing?

Any information on BIA Cache would be helpful ?

We have another environment on Rev 48 and there it says that Cache is disabled. so I am assuming that this feature was introduced in REv 49 or later

Note: this is different from DFI Cache. I see above behaviour irrespective of whether DFI was turned on or off.

- Saurabh Bansal

Edited by: Saurabh Bansal on Aug 25, 2009 10:39 PM

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  • Best Answer
    Posted on Aug 26, 2009 at 06:08 AM

    Hi Saurabh,

    at first I strongly recommend to use revision 51 or 52 because rev. 50 has a lot of bugs.

    You are right, up to Rev. 49 the caching feature is off by default.

    I haven´t any experience with this caching feature because we don´t activate it, but have you analyzed the query via rsrt with debug modus? There you can see where the most time is spent and in connection with this you can also use the performance trace in the python tool.

    If you have a look at this document you will find this:

    ...

    "Note that early tests by SAP suggest that the query-processing speed with BI

    accelerator is approximately the same as that with the OLAP Cache. However, the BI

    accelerator also provides additional flexibility and scalability. This suggests that even

    the planning and maintenance associated with OLAP Cache could disappear in

    deployments with the BI accelerator appliance. Although SAP itself does not make

    this recommendation at this time, if the processing times are indeed going to be

    proved to be the same, it seems that using the OLAP Cache loses its value."

    ...

    "BI accelerator may eliminate the need to deal with an OLAP Cache"

    This FAQ may also useful.

    Best Regards,

    Jens

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  • author's profile photo Former Member
    Former Member
    Posted on Sep 08, 2009 at 09:25 AM

    you wrote:

    ---

    "In noraml BWA system, there are

    only BW requests with structured data search. So for noraml BWA system,

    the TREX cache will not be used even you set the parameter use_cache=yes."

    But in our case, we never used Polestar for this system, still TREX Cache was used.

    ---

    I suppose, that the trexcache calls parameter in TrexIndexServer.ini of your installation have included olap searches as well,

    that's why BWA queries were cached in the IndexServers.

    <trexcache>

    use_cache = yes

    calls_to_cache = ... olap ...

    regards,

    G.

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