Oracle Data Compression on SID tables and Dimension Tables

Question

Hello Community,
We have had great success with Oracle compression on ODS tables that are no longer loaded.
We'd now like to move on to other types of BW tables that are very large.
OSS Note 701235 provides answers to questions concerning the possible use of Oracle compression together with SAP BW.
But the Note does not give suggestions for (or against) Oracle compression on SID tables or Dimension tables.
I believe both table types would exhibit the same behaviour : mostly inserts of new SID IDs and new DIM IDs, but few updates to existing SID or Dimension records.  If this is true, then both are good candidates for oracle compression. 
Do you also agree that this is the typical behaviour for SID tables and dimension tables ?  And that these types of tables are good candidates for Oracle compression in a large BW system ?
Thanks kindly!
Keith Helfrich

Answer 1

Hi all,
Although this is an old thread I stumbled on during my own investigations I can provide some answers to your questions.
Table candidates for compression are found by these criteria
       - Table size big enough?
       - Long lifetime of object planned ?
      - No or only rare structural changes for the table   ?
      - u201EUpdateu201C rate low : is your data mostly kind of u201Cread onlyu201D ?
--               for the wideley used rolling window partition techniques of
                  tables in BW this is not a problem: mostly INSERTu2019s in the
                 current partition not affecting other partitions
BW tables that can benefit from compression (see SAP notes 105047,701235)
       - PSA tables with data that must be saved for a longer time
       - ODS change log (no Updates of old data, only Inserts of new data)
       - u201Ehistoricalu201C cubes wich get no changes in table structure anymore
Limitations
         - normal Insert or Update statements are stored ALWAYS in uncompressed
                format and must be compressed separately ( <= Oracle10g )
         - Slight CPU overhead of compression, butu2026
         --      CPU consumption is more than compensated by doing less I/O as
               for Bulk loads or parallel processing
         --      SAP BW transformations took a significant amount of CPU for
                   overall load-time into cubes caused by the application server not
                   the database
          - Table must have not more than 255 fields
          - Adding columns with an initial value or dropping columns require
               uncompression of the complete table (strongest limitation)
Consider all this above and you can decide that tables that going through UPDATE's are
not good candidates for compression or tables that can change it's structure (like
Fact- or DIM tables) .
Now, my questions to you:
Wich Oracle version do you use?
Wich tool do you use for  Oracle compression?
BRspace (can you give an example ?)
ALTER ... MOVE COMPRESS
bye
yk