Size Category of Database Tables

In Data Class we have defined the kind of Data we are going to have for our table. Now, it’s time to decide the expected Volume of Data. We do it via Size Category of Database Tables.

Initially Every Table receives equal amount of allowed space. If the data exceeds the initial space provided then an extent of memory is provided to the table, the amount of extended memory will depend upon the size category we provide.

In this way we actually prevent creation of Large extended memory and thus reduce the wastage of data base space.

Definition

Initially every table have some memory allotted. Size Category tells us the amount of space that will be extended after the initial memory is filled.

What will happen if extended memory created is also filled?

Then a new extend will be created again with the memory equal to the size category provided as shown below:

Size Category of Database Tables

We have 3 Table with Size Category 0, 1, 2 respectively. The Initial memory allotted for all tables are equal but later on depending upon the Size Category the extent is provided in the data base.

How Multiple Extends affects the Data base?

A table with multiple extensions affects database in following ways:

  • Decreases System Performance: Data will be fetched from two different sources.
  • Increases Database management: Database Reorganization is required
  • Lowers Systems Availability: For Database reorganization, it is taken offline.

TYPES OF SIZE CATEGORY

 

Size Category Expected Rows
0 0 to 1,000
1 1,000 to 4,200
2 4,200 to 17,000
3 17,000 to 68,000
4 68,000 to 270,000
5 270,000 to 540,000
6 540,000 to 1,000,000
7 1,000,000 to 2,100,000
8 2,100,000 to 4,300,000
9 4,300,000 to 170,000,000

 

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