Managing DB Objects   «Prev  Next»
Lesson 3Data blocks
ObjectiveThe role of Oracle data blocks.

Oracle Data Blocks

The data block is the smallest unit of Oracle storage. All Oracle Input/Output (I/O) operates on the basis of one or more data blocks.
The data block is based on the underlying blocks in the operating system, as shown in the following MouseOver.

Data Blocks System Blocks

You can set the size of the Oracle data block for the entire database when you create the database.
A data block is made up of one more operating system blocks.
The size of the operating system block depends on the particular operating system on which you are running Oracle.

Configuring data blocks

The default data block size for an Oracle database is 2 KB, but Oracle can support data blocks up to 32 KB with standard hardware, and more with some hardware. Most databases use data blocks that are at least 4 KB.
The size of a data block affects the overall performance of your Oracle system. The larger the size of the data block, the more information is read, at a minimum, and the more operating system I/O operations may be necessary. If your database is used with mostly smaller rows, reduce the number of I/O operations by setting the data block size smaller. If your database is used with mostly larger pieces of data, such as BLOBs[1], set the data block size larger to avoid unnecessary additional I/O.
The next lesson discusses Oracle segments.

[1] BLOB: A binary large object (BLOB) is a large piece of data.