Oracle Database - (Data|Db|Logical|Oracle) Block or Page
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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 High Water Mark
Articles Related
Retrieval of block
Blocks may be retrieved and used by the database in one of two ways :
- current
- or consistent
A query will generally perform “Consistent Gets” and the term logical I/O refer often to it.
Current get
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|Current Get) Buffer Mode (CU)
Consistent get
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 : Consistent Gets