topic Question1 in Application Development and Automation Discussions

Question1

Former Member — Sun, 06 Apr 2008 03:38:51 GMT

Respected sir,

Plz help me to solve question as :

1.How many background jobs are running in your production system?

2.What is table buffer and single record buffer ?

3.What will observe with respect to buffer ?

4.If you see the same parameter value in all instance profiles what will you do ?

5.If you have observed enque overflow ? What will you do?

Re: Question1

Former Member — Sun, 06 Apr 2008 04:08:50 GMT

Hi Sandeep...

Ans to ur queries::

1> follow the following link to read about background jobs in production systems

http://help.sap.com/saphelp_nw70/helpdata/en/ed/a9bb3f8e236d3fe10000000a114084/content.htm

Re: Question1

Former Member — Sun, 06 Apr 2008 04:09:30 GMT

Ans to 2nd qstn>

Individual records of tables with single-record buffering are managed in the single-record table buffer TABLP.

Technical Implementation and Buffer Access

The single-record table buffer contains a central administrative structure, a table directory and the data area. The data area is organized in frames of a fixed size (default value 4 KB).

The table names are sorted alphabetically in the directory. The table entries are also stored sorted in the corresponding frames of the data area.

In a buffer access, a binary search is first used to find the entry in the table directory, followed by the corresponding frame and then the record searched for within the frame.

Frames can overflow in the data area if new data is inserted while adhering to the sort sequence. Such overflow frames have to be divided up and their administrative structure must be updated. This explains why the single-record table buffer is somewhat less efficient than the generic/full table buffer. In the single-record table buffer, the data records must be added one after the other while reorganizing the frame structure. In the generic/full buffer, however, all the data of a table is transferred in one step, already sorted by the database.

Managing Non-Existent Records

The single-record buffer also stores information about non-existent records of a table. If you attempt to access the table with a key that is not in the database, this information is stored in the buffer.

This is done with a flag that is added to every record stored in the buffer. The flag shows whether or not this record exists in the table. If you attempt to access a record that does not exist, an empty record is stored in the buffer with the corresponding key, and the flag is set to the value for a non-existent record. If you try to access this record again, the system sees in the buffer that this record does not exist in the database.

Single-record buffering is also recommended if you repeatedly try to access non-existent records of a table.

Displacement

If records of a table with single-record buffering are to be read and stored in the buffer, it might be necessary to remove other records from the buffer for space reasons. In this case, the records of the table that were least recently accessed are removed from the buffer.

Global Synchronization

The modifications made in the local buffers must be synchronized in distributed systems in order to keep the buffered data consistent. The general procedure for synchronization is described in Synchronization of Local Buffers.

The effect of different ABAP commands on the local and global synchronization of the single-record buffer is described below.

If changes are made with WHERE conditions (UPDATE dbtab WHERE ..., DELETE FROM dbtab WHERE ...), the entire table is invalidated in the buffer of the local server (server on which the command was submitted) and on all other servers at the time of the synchronization.

Changes without WHERE conditions (UPDATE dbtab, INSERT dbtab, DELETE dbtab) modify the corresponding records in the buffer of the local server and delete them in the buffers of all the other servers at the time of synchronization.

Modifications with a WHERE condition therefore place a much greater load on buffer management than those without a WHERE condition.

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Re: Question1

Former Member — Sun, 06 Apr 2008 04:10:47 GMT

Ans to qstn 2 continued>>>>

Table Buffer::

Use

The table buffer is located between the application and the database. Its goal is to cache portions of a database table in the application server to reduce database load and network communication. As you can see in the following figure, each server process of the J2EE Engine contains its own table buffer instance, which is shared among all threads of the server. Changes made to buffered data within one server process should be propagated to all other nodes to avoid inconsistencies in the remote buffers. The buffer synchronization mechanism used in the J2EE Engine guarantees that changes to buffered data are propagated to all remote buffers with a short delay.

The table buffer in a cluster of servers. Each cluster node has its own table buffer.

Activities

Using the Java Dictionary, you can enable buffering for individual tables. Furthermore, you can define the buffer granularity by specifying the columns that form the table’s generic buffer key. The data units that are stored in the buffer are called generic buffer areas. Buffering is transparent to the application program.

The first buffer access implicitly loads the data into the buffer so that a subsequent request can retrieve the data from the table buffer, rather than having to access the database. When a query is issued against a buffered table, the system checks if the query’s WHERE clause restricts the result set to a generic buffer area with respect to the generic key defined in this table. If this is the case, the query is issued against the table buffer instead of the database. If the respective generic buffer area is not yet in the buffer, then it is loaded into the buffer before the query is processed.

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Re: Question1

Former Member — Sun, 06 Apr 2008 04:12:31 GMT

To know about overflows , i suggest u to go through the following pdf

http://help.sap.com/printdocu/core/Print46c/en/data/pdf/BCCSTEQ/BCCSTEQ_PT.pdf

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