Data block fundamentals
The following gives insight into Data block fundamentals.
- Freelist: Used to manage free data blocks
- High water mark: Used to track the last data block with row data
- PCTFREE: Determines when to perform a freelist un-link
- PCTUSED: Determines when to perform a freelist re-link
- Extents table: Used to manage new object extents
Oracle manages the storage space in the datafiles of a database in units called data blocks. A data block is the smallest unit of data used
by a database.
In contrast, at the physical, operating system level, all data is stored in bytes. Each operating system has a block size. Oracle requests data in multiples of Oracle data blocks, not operating system blocks.
The standard block size is specified by the initialization parameter DB_BLOCK_SIZE. In addition, you can specify of up to five nonstandard block sizes. The data block sizes should be a multiple of the operating system's block size within the maximum limit to avoid unnecessary I/O. Oracle data blocks are the smallest units of storage that Oracle can use or allocate.
In contrast, at the physical, operating system level, all data is stored in bytes. Each operating system has a block size. Oracle requests data in multiples of Oracle data blocks, not operating system blocks.
The standard block size is specified by the initialization parameter DB_BLOCK_SIZE. In addition, you can specify of up to five nonstandard block sizes. The data block sizes should be a multiple of the operating system's block size within the maximum limit to avoid unnecessary I/O. Oracle data blocks are the smallest units of storage that Oracle can use or allocate.
