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Query Read mode

HI Experts,

What is QueryReadMode? In which Scenario we have to use QueryReadMode?

1.In which situation we have to create Aggregates and how do u know weather the cube has Aggregates or not?

2.In which situation we have to create Indexes and how do u see the indexes bitmap r Btree explain me Briep

3.In which situation we have to do Compression?how can i delete requests and how can i delete records from single request & from Multiple requests based on the fixed value.

4.In which situation we have to create Partitions and how do u know weather the cube has partions or not?

5.4.In which situation we have to create LINE-ITEM Dimentions.

please any body explain me these topics with example...................

what is BW STATISTICS explain me brief......

THANKS IN ADVANCE,

PriyaKodali

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  • Best Answer
    author's profile photo Former Member
    Former Member
    Posted on Nov 26, 2011 at 07:38 AM

    HI

    What is QueryReadMode?

    We use the query monitor to test or regenerate queries and query views, and to check or change query properties. With the query monitor you have the option of displaying technical information about queries

    Query Properties.

    In the Query Properties window of the Query Monitor, we can configure settings for the Read Mode, Cache Mode etc.

    The read mode of a query determines how often the OLAP Processor retrieves data from the database during query navigation. The read mode contains three types of read processes:

    Read all data (setting A: Query to Read All Data At Once)

    Reread the data (setting X: Query to Read Data During Navigation)

    Reread the data when expanding a hierarchy (setting H: Query to Read When You Navigate or Expand Hierarchies)

    WE USE T-CODE RSRT.

    (H) u2013 Query to read, when you read or expand hierarchies: In H mode, the detailed information within the nodes and sub-nodes of a hierarchy are read on demand (i.e., when you expand a hierarchy node). The amount of data transferred to the OLAP processor is the least of all the three categories. The downside is that the number of database reads increases as you keep expanding hierarchy nodes. SAP recommends setting queries to the H read mode. This is based on the empirical evidence of the relative performance of queries set to each of these modes.

    (X) u2013 Query to read data during navigation: In this mode, data are requested by the OLAP processor as

    dictated by every navigational step. The difference between X mode and H is that in the case of hierarchies, all the data on a leaf level are completely retrieved by the OLAP processor.

    (A) u2013 Query to read all data at once: There is only one read process in this mode. When you execute the query in the Business Explorer, all data in the main memory area of the OLAP processor that is needed for all possible navigational steps of this query is read. During navigation, all new navigational states are aggregated and calculated from the data from the main memory.

    The read mode Query to be read when you navigate or expand hierarchies significantly improves performance in almost all cases compared to the other two modes. The reason for this is that only the data the user wants to see is requested in this mode.

    What Is An Aggregate?

    An aggregate stores the dataset of an InfoCube redundantly in a summarized form. In this instance, summarization means the condensing of the original fact table of an Infocube to an aggregate table. This table no longer contains certain characteristics of the Infocube and has been summarized across attributes, or to characteristic values, or a hierarchy level.

    The summarization enables you to access the data of an InfoCube quickly when reporting. Aggregates are, therefore, tools for enhancing performance.

    Aggregates are created from logical data packets (requests). You can distinguish between the processes of filling and rolling up

    http://wiki.sdn.sap.com/wiki/display/BI/Aggregates--SAPBWQueryPerformance

    3. In which situation we have to create Indexes and how do u see the indexes bitmap r Btree explain me Briep

    Bit map and B-tree index - It is related to Cardinality.

    Cardinality means no. of predefined options for perticular Info Object.

    e.g Sex of person - Male or Female - we have only two options - so it will be considered as Low Cardinality.

    Document Number : their can be many document numbers depends on the no. of users. so it is considered as high cardinaltiy

    If low cardinality is their, Bit map index is used.

    If high cardinalty is their, B tree index is used.

    http://www.sdn.sap.com/irj/scn/go/portal/prtroot/docs/library/uuid/e0b28d18-f383-2c10-a780-a52349715b54?QuickLink=index&overridelayout=true

    http://help.sap.com/saphelp_erp2004/helpdata/en/cf/21eb47446011d189700000e8322d00/frameset.htm

    • 4. In which situation we have to do Compression?how can i delete requests and how can i delete records from single request & from Multiple requests based on the fixed value.*

    Compression improves Performance Tuning as it removes the redundant data. This improvement in the performance can be checked by RSRT and running the query with compression & without compression.

    http://www.sdn.sap.com/irj/scn/go/portal/prtroot/docs/library/uuid/c035d300-b477-2d10-0c92-f858f7f1b575?QuickLink=index&overridelayout=true

    http://www.sdn.sap.com/irj/scn/go/portal/prtroot/docs/library/uuid/c09b7019-4885-2e10-e2b8-fe1fef0643db?QuickLink=index&overridelayout=true

    deletion of compressed cube data

    5.In which situation we have to create LINE-ITEM Dimentions.

    http://www.sdn.sap.com/irj/scn/go/portal/prtroot/docs/library/uuid/005f3197-d3da-2e10-1a94-a5c62342f2aa?QuickLink=index&overridelayout=true

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  • Posted on Nov 26, 2011 at 08:37 AM

    Hi

    Query read mode is used to improve the query performance.Let me explain it with an example. Suppose u have some 10 characteristic and some 100keyfigures. and u placed some 2 characteristic IO in rows and 8 characteristics IO in columns and 100 keyfigures in column.

    So whenever u execute the query the OLAP processor has to fetch all the data of 10 characteristic and 100 keyfigures which may take some time . This can be achieved by using the query read mode "A".

    A: It means it will fetch all the records at one time.

    With this read mode , the query performance will be slow because it has to fetch all the records at one time.So this query mode is not recommended, if we want to improve the query performance.

    But initially i want to display the o/p of 10 rows(which is in columns ) and 100 keyfigures which in keyfigures . So the free characteristic data has to be displayed only when we drag and drop that characteristic into the resultset.So with this the query performance will be improved because intially it will be bring the data of which is present in the rows and column , inturn it will take less time to bring the data when compared to fetching the records with query read mode(A).

    This process of fetching the records is achieved with the help of X query read mode.

    Similarly H is also same as X , H is used for hierarchy.

    Hope u got it,

    Assign points ,

    Thanx & Regards,

    RaviChandra

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