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Tuesday, November 29, 2005

The concept of Table buffers – For functional consultants – Part one

First of all I would like to thank all my SAP friends from all over the world for the emails that you sent me. As well as I would like to thank SAP business community team for the motivation that they have given to me. Thank you guys! I really appreciate it.

Today I’ll talk about the concept of table buffers on SAP. This topic is pretty interesting and gives certain implications on ABAP programming model. I think it’s really useful to the functional consultants to have certain amount of knowledge on this subject.

As we all know, a well developed ERP system should try to optimize its performance by using every possible way. Especially the response time it takes to process the requests from the business user should be minimize as much as possible. By taking this factor into consideration SAP has designed the concept called ‘Table buffer’.

This concept has been developed by considering two main factors.

1. The network traffic between the application server and the database server

As I explained on my earlier posts the SAP database server and the application server can be located on two different physical servers. So every time the application server requests some data from the database, it should be transferred through the network from the database server to the application server which may lead to high network traffic on a typical SAP installation where multiple requests will be passed per second. This factor would slow down the system.

2. The database load

When the programs processed by the application server, directly deal with the tables on the database to manage the data, it increases the database load which will slow down the database’s performance. This will affect a program which uses a specific table in the database as well as other programs which try to use some different tables in the same database.

Solution for the issue

The concept of table buffer simply load the data of a database table into the application server’s RAM. So the programs would access the data from the application server’s RAM rather than directly from the database table.
By buffering data, we increase performance in two important ways:

1.The programs using the buffered data run faster because they don't have to wait for it to come from the database. This reduces delays waiting for the database and the network that connects it.

2.The other programs that need to access the database run faster because there is less load on the database and less traffic on the network.
According to the benchmark tests, buffering a table can cause a select statement to run 10 to 100 times faster or more.

The next question that SAP had was, whether to allow all the tables to be buffered or not. Obviously we all would say ‘Yes’. However, buffers are stored entirely on RAM, so space is limited by the amount of RAM available. In fact, there is so much more data than there is RAM, that tables must be buffered with caution to prevent overruns. If a buffer overruns, it might swap to disk, which can eradicate any performance gained by buffering. So SAP has developed this concept in such a way that each individual table can be configured to be buffered or not. But the tables containing a numeric data type as the primary key cannot be buffered

Buffering can be activated through the technical settings of any table. The following screenshot shows table T001, which has been activated to be buffered.

How does this concept work?

When an ABAP program issues an open sql statement, the application server will first check whether the table has been activated to be buffered or not, if the table has been activated to be buffered, the server will check the RAM for the buffered data.

If the buffer is available, the program will read the data from the RAM else it will read it from the database, populate the buffer and subsequently read from the buffer.

I think this post should have given you a basic idea about the table buffers. Definitely this concept improves the performance of the system, but we have to take certain facts into consideration when we try to activate the table buffer on any table. On my next post I will talk about the implications of table buffers in a more detailed way. As well as I will take a look at the multi application server environment and the table buffers.

Please send me your comments.


Anonymous said...

Excellent explanation..Keep it up..I have one more question on Finance side since u r FI consultant.

When we do goods receipt, we debit to Inventory a/c and Credit GR/IR. On receipt of invoice, we Dr. GR/IR and Credit Vendor a/c..Inventory a/c is defined as Balance Sheet a/c. If we want to find out the total purchases to reflect it in Trading/P&L account, how do we determine it from SAP?

It would be good idea if you can provide blog on how accouting entries generated in SAP are mapped in P&L a/c and Balance sheet. Try to cover business scenario with complete life cycle.
Regards- Kamlesh

Zahid said...

Excellent explaination in simple works. I like to ask a question, that as a functional consultant, what is the concept of using the SAP tables.

Anonymous said...

Thank you for the explanation about table buffering concept in SAP.
Besides those advantages of table buffering you mentioned in the paper, there are disadvantages you should specify clearly. This would help SAP users to have an general point of view about the concept, therefore they can determine where and when to use table buffering in a proper way.