Oracle Database - Block (Db Block or Data Block)

Articles which talk about block management.

At the finest level of granularity in the logical structure of an Oracle Database, the data is stored in data blocks.

One data block corresponds to a specific number of bytes of physical database space on disk. The standard block size is specified by the DB_BLOCK_SIZE initialization parameter. A common block size is 8k. In addition, you can specify up to four other block sizes. A database uses and allocates free database space in Oracle Database data blocks.

A block is also see as:

1. the individual rows,
2. the set of rows for each possible transaction on the block,
3. the entire set of rows in the block.

Blocks may be retrieved and used by the database in one of two ways :

• current
• or consistent

A query will generally perform ”Oracle Database - consistent gets statistic” and the term logical I/O refer often to it.

A current mode get is a retrieval of a block as it exists right now. You will see these most frequently during modification statement, which must update only the latest copy of the block.

Statistic : Oracle Database - Db Block Get Statistics

Consistent gets are the retrieval of blocks from the buffer_cache in “read consistent” mode and may include read asides to UNDO (rollback segments).

Statistic : Oracle Database - consistent gets statistic

• Consistent Gets
• Overview of Data Block