Tuesday, December 20, 2011

Technical Table Characteristics

Data class
The data class defines the physical area of the database (for ORACLE the TABLESPACE) in which your table is logically stored. If you choose a data class correctly, your table will automatically be assigned to the correct area when it is created on the database.
The most important data classes are (other than the system data):
APPL0 Master data
APPL1 Transaction data
APPL2 Organisational and customizing data
Master data is data which is frequently read, but rarely updated. Transaction data is data which is frequently updated. Organizational and customizing data is data which is defined when the system is initialized and then rarely changed.
There are two more data classes available, USR and USR1. These are reserved for user developments. The tables assigned to these data classes are stored in a tablespace for user developments.
Note:The data class only has an effect on table storage for the database systems ORACLE and INFORMIX.
Size category
The size category determines the probable space requirement for a table in the database.
You can select the categories 0 to 4 for your table. Each category is assigned a specific fixed storage area value in the database. When you create a table, initial space is saved for it in the database. If more space is required later as a result of data that has been entered, the storage space is increased in accordance with the category selected.
Press F4 on the field Size category to see the number of data records that can be maintained for the individual categories of your table without complications ensuing. These complications could be for example a reorganization becoming necessary because the maximum space to be reserved for the table was exceeded due to the maintained size category.
Buffering status
The buffering status specifies whether or not a table may be buffered.
This depends on how the table is used, for example on the expected volume of data in the table or on the type of access to a table. (mainly read or mainly write access to the table. In the latter case, for example, one would not select buffering).
You should therefore select:
- Buffering not allowed if a table may not be buffered.
- Buffering allowed but not activated if buffering is principally allowed for a table, but at the moment no buffering
should be active. The buffering type specified in this case is only a suggestion.
- Buffering allowed if the table should be buffered. In this case a buffering type must be specified.
Buffering type
The buffering type defines whether and how the table should be buffered.
There are the following types of buffering:
single-record buffering
generic area buffering
full buffering
In generic area buffering, a number of key fields between 1 and no. of key fields-1 must be specified.
Log data changes
The logging flag defines whether changes to the data records of a table should be logged. If logging is activated, every change (with UPDATE, DELETE) to an existing data record by a user or an application program is recorded in a log table in the database.
Note: Activating logging slows down accesses that change the table.
First of all, a record must be written in the log table for each change. Secondly, many users access this log table in parallel. This could cause lock situations even though the users are working with different application tables.
Logging Dependencies
Logging only takes place if parameter rec/client in the system profile is set correctly. Setting the flag on its own does not cause the table changes to be logged.
The existing logs can be displayed with Transaction Table history (SCU3).
Convert to transparent table or maintain transparency
This flag shows that a table should be transparent and that this attribute should be kept even after a change of release or an upgrade.
Transparent Table Use
You can convert pooled tables into transparent tables in a simple manner using the transparent flag. The pooled table must have ‘active’ status.
Activate the technical settings after setting the flag. You can now decide whether the table should be converted to a transparent table in the background or interactively for a pooled table.
If you want to change the type of a table whose transparent flag has been set, you must first reset the flag and activate the technical settings. The table type must then be changed explicitly and the table must be converted using the database utility.
Note: Only use the transparent flag if the table type is to change from pooled to transparent. You should never use the flag for other table conversions.

1 comment:

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