DB Size for a custom cluster table?

Question

Hi friends,
I have a requirement where in i need to store huge attachments into SAP DB.
For that i created a Custom cluster table just like INDX table and storing the binary read attachments(PDF/JPEG) into it.
Can some one help me how much size from DB side this table would take.
Suppose i am reading a PDF file of size 3.5 MB and storign this into my custom cluster table, which would span into 1200 records, what is the DB size taken by this ?
Appreciate any help on this.
SAP Version - 4.7EE
DB - DB2
OS - AIX
Regards,
Simha
Edited by: Simha on Aug 5, 2008 7:27 AM

Answer 1

Hi Simha,
simple question complex answer ....
The answer mainly depends on the length of the RAW column in the INDX type table. In my answer I assume that your database is running with the default of 16K tablespace page size.
(1) if the length of the RAW column is below 4K on a unicode system or below 12K in a non unicode system,
     the ABAP RAW column is mapped to a VARCHAR FOR BIT DATA column on database level.
     VARCHAR FOR BIT DATA colunms are buffered in the database buffer pool and can benefit from DB2 row compression.
     DB2 row compression may not help for PDF or JPEG data since this data is already compressed
     but buffering will provide better performance.
     Since VARCHAR FOR BIT DATA columns will be stored in the DB2 data pages, the overall space requirement will be
     minimal if the space in the 16K pages can be used optimal. E.g. if the size of our RAW column is 8,5 K and most rows
     contain values with maximun length in this column only one row can be stored per data page.
(2) if (1) does not apply, the ABAP RAW column is mapped to a LONG VARCHAR FOR BIT DATA
     column on database level.
     LONG data is stored in seperate LONG pages on database level. The LONG data is stored in blocks of
     512 bytes time 2^N ( 512, 1024, 2048, 4K , 8K, 16K ). The overall space requirement will be
     minimal if the space in the LONG blocks can be used optimal.
Given the explanation above I would guess that in worst case you may need a factor of 2 more space in the database than your document size. Each additional row will require some bytes overhead in the DB2 data pages and will create additional index entries. So you may want a large maximum size of your RAW column but this will give you LONG data types.
If read performance is not critical I would suggest to choose 16K as your size of the RAW column. This should completely fill the LONG blocks.
If read performance is more critical you should choose a small size for the RAW column ( e.g. 2K ) to benefit from data buffering and to avoid sparsely filled data pages.
Regards
               Frank