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robarivas's avatar
robarivas
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9 years ago

Large Table performance

I'm connecting to an IBM DB2 database (z/OS) via ODBC (cause I could never get the built-in connector to work). Most tables are viable. However, I cannot find a way to get the transactions table data...
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Phil_Seamark's avatar
Phil_Seamark
Icon for Microsoft Employee rankMicrosoft Employee
9 years ago

Hi robarivas,

 

Get rid of any columns that have unique ID's and if you have a column that is Date & Time, split that into two columns in Power Query (or just drop time altogether).

 

Do any of those help?

robarivas's avatar
robarivas
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9 years ago

Hi Phil_Seamark

 

I don't have those kinds of columns there because one of my first steps is to remove unneeded columns. The first step in which I perform a filter seems to cause query folding to stop happening.

  • yan's avatar
    yan
    Icon for Advocate I rankAdvocate I
    9 years ago

    Same issue here on a simple group by - no query folding so PD/PQ loads it all (20M rcds) before aggregating...

    I use Teradata through ODBC because it is the only option (still) to authenticate through LDAP.

     

    I bet it is due to the use of ODBC: PB/PQ doesn't know what DBMS it needs to translate the SQL too.

     

    (De)selecting columns though does translate to native SQL, probably because it is pretty standard. Anything invoking a WHERE or GROUP BY is not.

     

    The alternative is to copy/write your own "hardcoded" custom SQL in the data source step. Not ideal if you want business users to share a baseline and create their own steps (unless folding after that is not a must).

    • robarivas's avatar
      robarivas
      Icon for Post Patron rankPost Patron
      9 years ago

      Finally got a "proper" connection to the DB2 database...no more ODBC. I'm using the Microsoft driver. However, still no Query Folding!!! :smileyfrustrated:

       

      I wonder why. Anyone have a theory? Again, all I'm doing is a simple dates between filter on a date column (as my test of Query Folding).

      • robarivas's avatar
        robarivas
        Icon for Post Patron rankPost Patron
        9 years ago

        Would still love a response (Microsoft maybe??). The inability to leverage my transactions table seriously hampers my ability to fully adopt Power BI. One step or no step (i.e., Scheduled) Refresh is an impossibility because of this.

         

        And why would query folding happen for certain columns but not for others, such as (crucially) my Posting Date column???

  • robarivas's avatar
    robarivas
    Icon for Post Patron rankPost Patron
    9 years ago

    Why would Power Query stop Query Folding upon the simple act of filtering a column?

     

    let
         Source = Odbc.DataSource("dsn=ABCD", [HierarchicalNavigation=true]),
         ABC_Schema = Source{[Name="ABC",Kind="Schema"]}[Data],
         ABC1234_View = ABC_Schema{[Name="ABC1234",Kind="View"]}[Data],
         #"Removed Other Columns" = Table.SelectColumns(ABC1234_View,{"TX_DATE_POST", "ORDER_ID", "CORP_ID", "ORDER_SITE", "PRODUCT_ID", "ORDER_TYPE", "TX_ID", "TX_AMOUNT", "TX_QTY"}),
         #"Filtered Rows" = Table.SelectRows(#"Removed Other Columns", each [CORP_ID] = "54"),

     

    I'm querying an IBM DB2 (z/OS) database via ODBC (could never get the built-in connector to work).  The table (or view) I'm querying is an extremely large transactions table (nearly 900 million rows), I just want to pull a subset but cannot because the filtering takes forever. I know folding is not working because when I right click on the filtering step the "View Native Query" option is dithered out. The steps prior, however, are folding because on those steps the "View Native Query" option is selectable.