Monday, October 29, 2012

ASO Partial Data Clears Using MaxL and MDX

The Essbase 11.1 release brought us the ability to do partial data clears within an ASO database.  Gone are the days of using report scripts or the Excel Add-In to clear data.  There a couple of posts out there on other sites about how to use MaxL and MDX to do a partial data clear, but most of them speak to the simple clear script, performing a restriction using one dimension.  What happens when you need to define your data clear a little more precisely?

Let's start with the basics of data clears in an ASO Essbase cube.  There are two types of data clears you can perform, a logical delete and a physical delete.  A physical delete removes the input cells in the specified region, whereas a logical delete creates a new slice with an exact offset of the input cells you are trying clear.  When you retrieve the data both slices are netted together and you get zeros.  The technical reference notes that a physical delete completes in a time proportional to the size of input data while the logical completes in a time proportional with the size of data being cleared.  For this reason, a physical data clear is suggested when removing large slices of data.  It is also warned that a logical delete will increase the size of your database.  Both of these should be taken into consideration when doing a partial data clear.

Now on to the fun stuff…

The MaxL Script Editor can be used to perform the clear.  The syntax to be used is:

alter database . clear data in region '{MDX set expression}' [physical]

Your appname and database name should be placed in single quotes.  The MDX set expression is the definition of the data you want to clear.  Physical is an optional keyword that should be used when performing a physical clear.  The most difficult part of this syntax is the MDX set expression.

First and foremost, a set must have curly brackets around it.  Second, it has to be one of the prescribed MDX functions that return a set.  Remembering those two things, building the MDX set expressions becomes easier.

Using the ASOSamp application here are a few examples progressively showing you how you can restrict your script more and more precisely:
  • If you wanted to remove all Qtr4 data (regardless of year or any other dimension) your command would look like this:
alter database 'ASOsamp'.'Sample' clear data in region '{[Qtr4]}' Physical
·         If you wanted to remove only Qtr4 for current year (regardless of any other dimension) your command would look like this:
alter database 'ASOsamp'.'Sample' clear data in region 'Crossjoin({[Qtr4]},{[Curr Year]})' Physical
·         If you wanted to remove Qtr3 and Qtr4 for current year (regardless of any other dimension) your command could look like any of these:

o   alter database 'ASOsamp'.'Sample' clear data in region 'Crossjoin({[Qtr3]:[Qtr4]},{[Curr Year]})' Physical
o   alter database 'ASOsamp'.'Sample' clear data in region 'Crossjoin({[2nd Half].Children},{[Curr Year]})' Physical
o   alter database 'ASOsamp'.'Sample' clear data in region 'Crossjoin({MemberRange([Qtr3],[Qtr4])},{[Curr Year]})' Physical

·         If you wanted to remove Qtr3 and Qtr4 units for current year (regardless of any other dimension) your command could look like this:

alter database 'ASOsamp'.'Sample' clear data in region 'Crossjoin(Crossjoin({[Qtr4]},{[Curr Year]}),{[Units]})' Physical 

·         If you wanted to remove Qtr3 and Qtr4 units for current year (regardless of any other dimension) your command could look like this:

alter database 'ASOsamp'.'Sample' clear data in region 'Crossjoin(Crossjoin(Crossjoin({[Qtr4]},{[Curr Year]}),{[Units]}),{Descendants([Online])})' Physical

Keeping in mind the basics of MDX scripts is the key to getting your clear script defined down to a more granular level.  It is also important to note that the more complex your MDX is the longer your clear script may take to run.  If the data set being cleared is going to be very small you may want to use a logical delete as the increase to your database size will not be as noticeable.  If you are going to delete a large chunk of data, the physical delete may make more sense as a new large slice may take up a lot of memory and impact performance.

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