Download CMPT 454 Q1 - Introduction, Memory, & HDD: Exercises and Questions and more Exams Database Management Systems (DBMS) in PDF only on Docsity!
CMPT 454 Q1 - Introduction, Memory, & HDD 100% Verified
T or F: Single queries can either be on one or more tables - Answer T Instead of reading all records in a table and returning all those that match, what can we do? -Answer Use an index
Multiple table queries generally entails _________ - Answer joins What is the time complexity of the naive algorithm of a join? - Answer O(n^2) What is a transaction? - Answer A single logical unit of work Transactions are often composed of multiple ___________. - Answer actions T or F: An OLTP usually is accessed by only one user at a time - Answer False. Multiple usersconcurrently
What is a benefit of concurrent transactions? - Answer 1. Increases throughput (number oftransactions processed over time)
What is a disadvantage of concurrent transactions? - Answer Can leave database in aninconsistent state
What does ACID stand for and what is it? - Answer Atomic, Consistent, Isolated, Durable. Transactions should maintain these properties.
What a system failure occurs, what must happen to a database? - Answer 1. Must recover
- Must be guaranteed to be in a consistent state after recovery Where is processing performed? - Answer Main memory A transaction completed in main memory is lost if ...? - Answer It has not been written to disc What makes a database inconsistent? - Answer When some of a transactions' actions arewritten to disk before the transaction is complete. These transactions must be rolled back.
Where are schemas defined? - Answer In the database How are schemas created? - Answer Running a CREATE A TABLE statement or using the DBMSGUI
A schema is associated with one or more constraints. Which are they? - Answer 1. Primary key
- Foreign key
- Other constraints What does a DBMS do? - Answer 1. Facilitates access to DBs
- Maps the conceptual to the physical view (data stored in main memory or secondary storage)
- Responsible for accessing data from storage devices What are the two major alternatives for the interface between DBMS and application? - Answer1. Embedded
- Application accesses the DB directly via API call
- Linked to the application at compile time
- Tiered client-server
Disadvantage:
- Expensive Tertiary storage should have ________ and _________. - Answer Large capacity, low cost What are some examples of tertiary storage devices? - Answer 1. Cloud storage
- Optical drives (CDs and DVDs)
- Magnetic tape What is a major advantage of persistent memory? - Answer It is non-volatile: retains data evenif there is a break in power supply
T or F: Main memory is bigger than persistent storage - Answer F. Much smaller thanpersistent storage
Database data must be transferred between ______________ and ______________. - Answer Mainmemory and storage
What does transient memory mean? - Answer Memory that is both persistent and working Where are operations like read, update, write performed? - Answer Main memory What are cylinders in an HDD? - Answer Set of tracks with same diameter on all surfaces Where is control information located? - Answer In the fixed-sized gaps that separate blocks How can blocks be addressed? - Answer By cylinder number
What do blocks map to? - Answer Pages T or F: When data from a disk is read into the main memory, only the desired record is read intothe main memory. - Answer F. The block in which the record resides gets written into main memory What must happen before most writes? - Answer An initial read of a disk block How many disk heads can read or write at a time? - Answer One If there are 3 platters in an HDD, how many disk heads are there? - Answer 6, one for eachsurface
What are the steps to access a block on a disk? - Answer 1. Disk head pivots over the desiredtrack (seek time)
- Wait for leading edge of block to reach the disk head (rotational delay)
- The desired block is read as it passes underneath the disk head (transfer time) What is a disk controller? - Answer The processor that controls the drive How do you calculate maximum rotational delay? - Answer 1/RPM * 60s How do you find average rotational delay? - Answer 1/2 * max rotational delay What is the minimum seek time? - Answer 0 - the disk head is on the desired track What is maximum seek time? - Answer The time it takes for disk head to move from innermostto outermost track
- Write failure
- sector cannot be written to or retrieved (caused by a power failure)
- Disk crash
