Distributed Database Systems Quiz 2

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Questions and Answers

What is the main purpose of concurrency control algorithms in a distributed database system?

To enforce the durability property for distributed transactions

To enforce the atomicity property for concurrent transactions

To enforce the consistency property for distributed transactions

To enforce the isolation property for concurrent transactions (correct)

Which property of reliability measures ensures that once a transaction is committed, its changes are permanent and persistent, even after system failures?

Durability (correct)

Isolation

Atomicity

Consistency

What is the primary function of distributed transaction processing in a distributed database system?

Optimizing query processing

Enforcing data replication

Managing concurrent transactions (correct)

Ensuring data integrity

Which aspect of data management in a distributed database system aims to handle large volumes of data from different sources in a scalable and efficient manner?

Big Data Processing Signup and view all the answers

What is the primary role of data replication in a distributed database system?

Improving data availability Signup and view all the answers

In terms of distributed database systems, what does integrity enforcement primarily aim to ensure?

Correctness of transactions on the database Signup and view all the answers

In a timestamp-based concurrency control algorithm, how is the serialization order established?

By assigning each transaction a unique timestamp at initiation Signup and view all the answers

What is the preferred method for timestamp assignment in a distributed DBMS to maintain uniqueness?

Using the system clock values of each system Signup and view all the answers

What is the two-tuple form of a timestamp in the context of assigning timestamps based on local counters?

Local counter value, site identifier Signup and view all the answers

What does the basic timestamp ordering algorithm try to achieve?

To execute an operation as soon as it receives it Signup and view all the answers

According to the TO Rule in the basic TO algorithm, when is operation Oij executed before Okl?

When ts(Ti) < ts(Tk) Signup and view all the answers

What does a scheduler enforcing the TO rule do when it encounters a new operation?

Checks it against conflicting operations and accepts it if the transaction is younger than all conflicting ones Signup and view all the answers

What is the purpose of assigning read and write timestamps to each data item in the basic TO algorithm?

To keep track of which transactions have read or written a specific data item Signup and view all the answers

What is a drawback of the basic TO algorithm despite its deadlock freedom?

It can potentially lead to numerous restarts of a transaction Signup and view all the answers

What does the conservative TO algorithms attempt to lower?

The number of transaction restarts Signup and view all the answers

What does the conservative TO algorithms do with operations instead of causing them to wait?

Delays each operation until there are no conflicting operations Signup and view all the answers

According to the conservative TO algorithms, what does it delay each operation until?

There are no conflicting operations Signup and view all the answers

What do conservative TO algorithms attempt to achieve?

To minimize system overhead by reducing restarts Signup and view all the answers

Study Notes

Concurrency Control in Distributed Database Systems

The main purpose of concurrency control algorithms is to manage concurrent access to shared data in a distributed database system.

Reliability Measures

The property of reliability measures that ensures once a transaction is committed, its changes are permanent and persistent, even after system failures, is durability.

Distributed Transaction Processing

The primary function of distributed transaction processing is to manage multiple transactions executing concurrently in a distributed database system.

Data Management

Data management in a distributed database system aims to handle large volumes of data from different sources in a scalable and efficient manner, particularly focusing on data integration.

Data Replication

The primary role of data replication in a distributed database system is to maintain multiple copies of data to improve availability and performance.

Integrity Enforcement

Integrity enforcement in a distributed database system primarily aims to ensure data consistency and correctness.

Timestamp-Based Concurrency Control Algorithm

In a timestamp-based concurrency control algorithm, the serialization order is established by assigning a unique timestamp to each transaction.
The preferred method for timestamp assignment in a distributed DBMS is to maintain uniqueness by using a combination of a unique site identifier and a local timestamp.
The two-tuple form of a timestamp in the context of assigning timestamps based on local counters is (site-id, local-timestamp).

Basic Timestamp Ordering (TO) Algorithm

The basic timestamp ordering algorithm tries to achieve a serialization order that is consistent with the timestamp order.
According to the TO Rule, operation Oij is executed before Okl if the timestamp of Oij is less than the timestamp of Okl.
When a scheduler encounters a new operation, it executes it if its timestamp is the smallest among all pending operations.
Assigning read and write timestamps to each data item in the basic TO algorithm ensures that the system maintains a consistent serialization order.

Drawbacks and Enhancements

A drawback of the basic TO algorithm is that it is prone to starvation, where a transaction may be indefinitely postponed due to higher-timestamp transactions.
The conservative TO algorithms attempt to lower the possibility of starvation by allowing operations to proceed if they do not conflict with already committed transactions.
Instead of causing operations to wait, conservative TO algorithms execute them as soon as possible while maintaining a consistent serialization order.
According to the conservative TO algorithms, each operation is delayed until its timestamp is smaller than all other timestamps of operations that have been executed or are currently executing.
Conservative TO algorithms aim to achieve a higher level of concurrency while maintaining a consistent serialization order.

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Description

Test your knowledge of distributed database systems with this quiz focusing on topics such as introduction to distributed database, design, query processing, transaction processing, concurrency control, DBMS reliability, data replication, big data processing, and web data management.