- Assume (for now):
fixed length records:
Each attribute field is fixed length
- Fact:
- (Data) Records are stored in (disk) blocks
Graphically:
- File:
- A file consists of
one or more blocks
- The blocks of a file
are stored in
directory entries
Graphically:
block numbers <-------------------> +-----------+-------------------+-+-+-+-+-+ ...... +-+ | Filename | owner/access info | | | | | | | | +-----------+-------------------+-+-+-+-+-+ ...... +-+
- A file consists of
one or more blocks
- Structure of a block:
- Block header
(with information on the
records stored in the
block
- The records
Graphically:
- Block header
(with information on the
records stored in the
block
- Unspanned record storage:
- Every records are
stored within
one block
- I.e.: a record does not span over multiple blocks
- Every records are
stored within
one block
- Spanned record storage:
- Some records are
stored using
multiple blocks
- I.e.: a record can span over multiple blocks
- Some records are
stored using
multiple blocks
- Illustrated:
- How to store
spanned record:
- Format of a stored record:
- Example:
- A block of a file can store:
- Records of the
same relation
- Records of the different relation
- Records of the
same relation
- Clustered file:
- A file that stores
records of
one relation
- A file that stores
records of
one relation
- Unclustered file:
(less common)
- A file that stores
records of
multiple relation
- A file that stores
records of
multiple relation
- Block header:
- Each block has a
block header
- Information stored in a
block header:
- Information on
the role of the
block
(e.g., overflow block
- Information on the
source relation of each
record stored in the nlock
- The locations (offsets) of
the records stored in the
block
- Link(s) to other blocks (e.g., B+-tree - later)
- Information on
the role of the
block
(e.g., overflow block
- Each block has a
block header