week 3 - Why Distribution? Flashcards
Four items that make up a distributed database system
1) Availability
2) Scalability
3) Reliability/ Fault Tolerance
4) Transparency
Why do corporations use distribution in databases?
1) It prevents data collisions for quicker updates.
2) It helps by allowing a better understanding of data around data within an organization.
3) Distributed databases can avoid large traffic because the replicated data can be accessed locally.
3) Distributed databases can avoid large traffic because the replicated data can be accessed locally.
1.Question 1
What does transparency refer to in database terminology?
1) Separation of higher level semantics of a database system from the lower level implementation issues.
2) The ability of users to see the details of how a database system works.
3) The ability of users to manage the details of lower level database implementation.
4) The ability of users to see where pieces of data are stored in a distributed database system.
1) Separation of higher level semantics of a database system from the lower level implementation issues.
What does scalability refer to in database terminology?
1) The ability of a database system to expand and serve more users.
2) The ability of a database system to provide faster access speed.
3) The ability of a database system to provide better access with a minimum quality of service guarantee.
4) The ability of a database system to provide the same level of service with a lower cost.
1) The ability of a database system to expand and serve more users.
What is Horizontal Fragmentation
Split rows of the table into two(+) rows
say half the rows go into one table and half go into another table
What is Vertical Fragmentation
Spit columns of the table into two(+) tables
Which comes first Fragmentation or Replication
Fragmentation
Three main properties of good Fragmentation
1) Completeness
2) Reconstruction
3) Disjointness
Completeness of Fragmentation
no data item would be lost
Reconstruction of Fragmentation
You need some element that you can use to create the relationship
Disjointness of Fragmentation
No supplicates
Why is fragmentation a useful concept in distributed database design?
1) It makes data easier to store through data chunking.
2) It reduces disk space utilization and allows for easy access to data.
3) It allows data to be quickly archived in the cloud.
2) It reduces disk space utilization and allows for easy access to data.
database selection symbol
Sigma(σ)
simple predicates
From original table (R) (maybe what they are using to for a key)
minterm predicates
What are the fragments (what you use to filter out the selection ?)
Derived Horizontal Fragmentation
Derived Horizontal Fragmentation
Is defined on a member relation of a link according to a selection operation specified on its owner• It is important to remember two points – First, the link between the owner and the member relations is defined as an equi-join
Create new join tables
Two advantages of replication
1) Increased availability
2) Faster query evaluation
3 Disadvantage of f replication
1) Updates are challenging
2) Transaction processing
3) Concurrency control can be an issue
What is a sharded deployment of a database?
1) A partial replication where each fragment resides at one site.
2) Each fragment resides in one site only.
3) A full replication where each fragment resides at each site.
2) Each fragment resides in one site only.
Is replication good if you have a lot of queries
Yes
What is the main disadvantage of full replication?
1) It requires less disk space to perform.
2) The process to perform a single update is slower since it must be updated on different databases to keep the copies consistent.
3) There is less data movement over a network.
2) The process to perform a single update is slower since it must be updated on different databases to keep the copies consistent.
Best Questions 3 for placement of Fragments
1) minimize query response time
2) maximize throughout?
3) minimize some cost?
