Different tables in Database dictionary

[former_member577909]

• Major differnece bewteen Transparant and cluster/pooled tables, and in real practice where does these tables used.

Thankyou for your time in giving the answers.

Bhaskar.

[Former Member]

Hi ,

Transparent tables are those table which have one to one mapping with the tables in the database. so this means that if we see a transparent table in SE11 or other similar transations , then there is a table with the same name in the database .

Pooled and Clustered tables have a one to many relation to tables in the database , it basically means for one table in DDIC there will be more than one table in the database.

The main difference between pooled and clustred tables is that in clustred table there shold be a relationship between the table which form a cluster , where as in pooled tables is not necessary to have this relationship , it just acts as a common interfcae to many table in the database , pooled tables are basically used to combine together tables which do not strore large volume of data , where as clustered tables store large volume of data , as the data is stored in various tables as clusters.

Regadrs

Arun

Message was edited by:

Arun R

[Former Member]

Hi Bhaskar,

Please refer the links,

Hope this helps..

Regards,

Hema.

• Reward points if it is useful.

[Former Member]

Examples of Pooled and Cluster tables:

CDHDR and CDPOS tables are stored in the table cluster CDCLS.

TRMAC is pooled table.

Pooled Table:

A pooled table in R/3 has a many-to-one relationship with a table in the database (see Figures 3.1 and 3.2). For one table in the database, there are many tables in the R/3 Data Dictionary. The table in the database has a different name than the tables in the DDIC, it has a different number of fields, and the fields have different names as well. Pooled tables are an SAP proprietary construct.

When you look at a pooled table in R/3, you see a description of a table. However, in the database, it is stored along with other pooled tables in a single table called a table pool. A table pool is a database table with a special structure that enables the data of many R/3 tables to be stored within it. It can only hold pooled tables.

R/3 uses table pools to hold a large number (tens to thousands) of very small tables (about 10 to 100 rows each). Table pools reduce the amount of database resources needed when many small tables have to be open at the same time. SAP uses them for system data. You might create a table pool if you need to create hundreds of small tables that each hold only a few rows of data. To implement these small tables as pooled tables, you first create the definition of a table pool in R/3 to hold them all. When activated, an associated single table (the table pool) will be created in the database. You can then define pooled tables within R/3 and assign them all to your table pool.

Pooled tables are primarily used by SAP to hold customizing data.

Cluster Table:

A cluster table is similar to a pooled table. It has a many-to-one relationship with a table in the database. Many cluster tables are stored in a single table in the database called a table cluster.

A table cluster is similar to a table pool. It holds many tables within it. The tables it holds are all cluster tables.

Like pooled tables, cluster tables are another proprietary SAP construct. They are used to hold data from a few (approximately 2 to 10) very large tables. They would be used when these tables have a part of their primary keys in common, and if the data in these tables are all accessed simultaneously.

Table clusters contain fewer tables than table pools and, unlike table pools, the primary key of each table within the table cluster begins with the same field or fields. Rows from the cluster tables are combined into a single row in the table cluster. The rows are combined based on the part of the primary key they have in common. Thus, when a row is read from any one of the tables in the cluster, all related rows in all cluster tables are also retrieved, but only a single I/O is needed.

A cluster is advantageous in the case where data is accessed from multiple tables simultaneously and those tables have at least one of their primary key fields in common. Cluster tables reduce the number of database reads and thereby improve performance.

Restrictions on Pooled and Cluster Tables

1. Pooled and cluster tables are usually used only by SAP and not used by customers, probably because of the proprietary format of these tables within the database and because of technical restrictions placed upon their use within ABAP/4 programs. On a pooled or cluster table:

2. Secondary indexes cannot be created.

3. You cannot use the ABAP/4 constructs select distinct or group by.

4.You cannot use native SQL.

5.You cannot specify field names after the order by clause. order by primary key is the only permitted variation.

To know different between all the three types, please have a look at below link:

<a href="http://www.sap-img.com/abap/the-different-types-of-sap-tables.htm">Different Tablesin SAP</a>

Best Regards,

Vibha

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