Chapter 12 (File Management) Flashcards
What are some desirable properties of files?
Long-term existence
Shareable between processes
Structure
What operation allows a process to perform functions on a file?
Open
What is a field?
Basic element of data containing a single value
T/F A field can only be fixed length
F, fixed or variable length
What is a record?
Collection of related fields treated as a unit
T/F A record cannot be variable length
F, it can
What is a file?
Collection of similar records treated as a single entity
What is a database?
Collection of related data (1 or more files)
What are the criteria for choosing a file organization?
Rapid access
Ease of update
Economy of storage
Simple maintenance
Reliability
List the five fundamental file organizations
Pile
Sequential file
Indexed sequential file
Indexed file
Direct or hashed file
How does pile collect data?
In the order it arrives
How is data accessed in pile?
Exhaustive search
What is the purpose of pile?
Accumulate a mass of data and save it
Which file organization may be useful to store data prior to processing it?
Pile
T/F In a sequential file, some fields are different
F, all are the same
What are the attributes of a sequential file?
Field names and lengths
Where are new records placed for a sequential file?
Log file or transaction file
Where is a sequential file useful?
Batch processing
How can additions be handled in an indexed sequential file?
Overflow file
What’s special about an indexed sequential file?
Reduces time to access a single record while still providing sequential processing
What’s the difference between a partial and exhaustive index?
Partial index only has pointers to records having the field of interest. Exhaustive index has pointers to every record
When are direct or hash file mostly useful?
If records are only accessed one at a time
How are indexes often implemented?
B-trees
What’s the primary benefit of the B-tree for indexes?
Fewer disk accesses
What is a directory?
A file owned by the OS and managed by the file management system
What information does a directory contain?
Attributes, location, and ownership
What are some directory operations?
Search
Create file
Delete file
List directory
Update directory
T/F Every level of a directory structure may contain files and subdirectories
T
What are two issues with file sharing?
Access rights
Simultaneous access
What are the typical classes for access rights?
Specific user
Group of users
All
What are some examples of access rights?
None
Knowledge
Execution
Reading
Appending
Updating
Changing protection
Deletion
What are two approaches for simultaneous access?
Lock the file when it is to be updated
Lock individual records during update
When is a blocking of records performed?
When writing data
List three blocking methods
Fixed
Variable-length spanned
Variable-length unspanned
What are the properties of the variable-length spanned blocking method?
Variable-length records which may span blocks
Unlimited record size
May require multiple I/O’s
What are the properties of the variable-length unspanned blocking method?
Variable-length records which do not span blocks
May cause internal fragmentation
What does a file consist of?
Collection of blocks
What are two management issues for secondary storage management?
Allocating blocks to files
Maintaining a list of free blocks
What are some file allocation issues?
Whether to allocate the maximum space required all at once, or to allocate space in portions
If portions are used, how big should a portion be?
If portions are used, how to keep track of the portions?
What are some techniques for free space management?
Bit tables
Chained free portions
Indexing
Free block list
