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.
The data block sizes should be a multiple of the operating system's block size.
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:
- the individual rows,
- the set of rows for each possible transaction on the block,
- the entire set of rows in the block.
If you had 200,000 rows in a table, deleted half of them, then the table would still 'own' the same number of blocks. See Oracle Database - High Water Mark (HWM) - boundary between used and unused space
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.
Consistent gets are the retrieval of blocks from the buffer_cache in “read consistent” mode and may include read asides to UNDO (rollback segments).