Oracle “formats” the database files into a number of Oracle blocks when they are first created—making it easier for the RDBMS software to manage the files and easier to read data into the memory areas.

The block size should be a multiple of the operating system block size. Regardless of the block size, the entire block is not available for holding data; Oracle takes up some space to manage the contents of the block. This block header has a minimum size, but it can grow.
These Oracle blocks are the smallest unit of storage. Increasing the Oracle block size can improve performance, but it should be done only when the database is first created.
Each Oracle block is numbered sequentially for each database file starting at 1. Two blocks can have the same block address if they are in different database files.
http://walkin-intervie w.com/database-interview-quest ions/what-is-oracle-block-can- two-oracle-blocks-have-the-sam e-address/

Answered by Nishu's , an ibibo Master, at 11:18 PM on October 26, 2008

Oracle “formats” the database files into a number of Oracle blocks when they are first created—making it easier for the RDBMS software to manage the files and easier to read data into the memory areas.

The block size should be a multiple of the operating system block size. Regardless of the block size, the entire block is not available for holding data; Oracle takes up some space to manage the contents of the block. This block header has a minimum size, but it can grow.
These Oracle blocks are the smallest unit of storage. Increasing the Oracle block size can improve performance, but it should be done only when the database is first created.
Each Oracle block is numbered sequentially for each database file starting at 1. Two blocks can have the same block address if they are in different database files.

Answered by Alok , an ibibo Citizen, at 7:30 PM on October 22, 2008

Oracle “formats” the database files into a number of Oracle blocks when they are first created—making it easier for the RDBMS software to manage the files and easier to read data into the memory areas.
The block size should be a multiple of the operating system block size. Regardless of the block size, the entire block is not available for holding data; Oracle takes up some space to manage the contents of the block. This block header has a minimum size, but it can grow.
These Oracle blocks are the smallest unit of storage. Increasing the Oracle block size can improve performance, but it should be done only when the database is first created.
Each Oracle block is numbered sequentially for each database file starting at 1. Two blocks can have the same block address if they are in different database files.

Answered by Hem@nt .... , an ibibo Master, at 10:18 AM on October 22, 2008

well vinay !Oracle “formats” the database files into a number of Oracle blocks when they are first created—making it easier for the RDBMS software to manage the files and easier to read data into the memory areas.

The block size should be a multiple of the operating system block size. Regardless of the block size, the entire block is not available for holding data; Oracle takes up some space to manage the contents of the block. This block header has a minimum size, but it can grow.
These Oracle blocks are the smallest unit of storage. Increasing the Oracle block size can improve performance, but it should be done only when the database is first created.
Each Oracle block is numbered sequentially for each database file starting at 1. Two blocks can have the same block address if they are in different database files.

Answered by raj u , an ibibo Master, at 10:14 AM on October 22, 2008

well, The Operating System Block size is the minimum unit of operation (read /write) by the OS and is a property of the OS file system. While creating an Oracle database we have to choose the 'Data Base Block Size' as a multiple of the Operating System Block size. The minimum unit of operation (read /write) by the Oracle database would be this 'Oracle Block', and not the OS block. Once set, the 'Data Base Block Size' cannot be changed during the life of the database (except in the case of Oracle 9i). To decide on a suitable block size for the database, we take into consideration factors like the size of the database and the concurrent number of transactions expected. Proper block sizing and its use are very important from the tuning point of view.
The availability of the block in the "free list" is determined by the PCTFREE value. Initially, an empty block will be listed in the free list table, and it will continue to remain there until the free space reaches the PCTFREE value. When the free space reaches the PCTFREE value, the block is removed from the free list, and it is re-listed in the free list table when the volume of data in the block comes below the PCTUSED value. Oracle uses the free list to increase the performance. So for every insert operation, Oracle needs to search for the free blocks only from the 'free list' table instead of searching all blocks.
source site: http://www.dbasupport.com/oracle/or a9i/rowchaining.shtml

Answered by Uttam , an ibibo Master, at 9:35 AM on October 22, 2008

Another name for an Oracle data block is a "logical block", but you won't hear many people call it that and I'm glad. Because for now I want you to consider it a physical construct in our layers of logical and physical pieces.

That's because data blocks impact/influence/determine storage, backup and recovery, SQL performance, memory usage, I/O, scalability, and probably anything else I haven't mentioned.

And the cool thing is, data blocks are very easy to understand.

yes of course two oracle blocks can have the same address if they are from different database files.

Answered by Koushik , an ibibo Specialist, at 9:05 AM on October 22, 2008

Oracle "formats" the database files into a number of Oracle blocks when they are first created�making it easier for the RDBMS software to manage the files and easier to read data into the memory areas.
The block size should be a multiple of the operating system block size. Regardless of the block size, the entire block is not available for holding data; Oracle takes up some space to manage the contents of the block. This block header has a minimum size, but it can grow.
These Oracle blocks are the smallest unit of storage. Increasing the Oracle block size can improve performance, but it should be done only when the database is first created.
Each Oracle block is numbered sequentially for each database file starting at 1. Two blocks can have the same block address if they are in different database files.

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Answered by Deepak , an ibibo Master, at 7:01 AM on October 22, 2008

Oracle "formats" the database files into a number of Oracle blocks when they are first created—making it easier for the RDBMS software to manage the files and easier to read data into the memory areas.
The block size should be a multiple of the operating system block size. Regardless of the block size, the entire block is not available for holding data; Oracle takes up some space to manage the contents of the block. This block header has a minimum size, but it can grow.
These Oracle blocks are the smallest unit of storage. Increasing the Oracle block size can improve performance, but it should be done only when the database is first created.
Each Oracle block is numbered sequentially for each database file starting at 1. Two blocks can have the same block address if they are in different database files.

Answered by Anju Singh , an ibibo Master, at 6:39 AM on October 22, 2008