Distributed Databases - Database MCQ Questions and answers- Technical Aptitude

A distributed database is a single logical database that is spread across multiple locations and interconnected by a network, enabling distributed data processing and access.

Option A: A single logical database that is spread to multiple locations and is interconnected by a network
This option correctly describes a distributed database. It emphasizes that although the database is distributed across multiple locations, it functions as a single logical unit, allowing users to access and manipulate data as if it were stored in a centralized location. The distributed nature of the database enables data sharing, replication, and distributed query processing over a network.

Option B: A loose collection of file that is spread to multiple locations and is interconnected by a network
This option describes a distributed file system rather than a distributed database. In a distributed file system, files are distributed across multiple locations and interconnected by a network, but there is no centralized control or management of data as in a distributed database.

Option C: A single logical database that is limited to one location
This option describes a centralized database rather than a distributed database. In a centralized database, all data is stored and managed within a single location or server, without distributed storage or processing capabilities.

Option D: A loose collection of file that is limited to one location
This option describes a local file system rather than a distributed database. In a local file system, files are stored and managed within a single location or device, with no distribution of data across multiple locations.

Therefore, in response to the question, the correct option is Option A: A single logical database that is spread to multiple locations and is interconnected by a network.

A semijoin is a relational operation used in distributed database systems to reduce the amount of data transferred between sites while performing join operations.

Option A: Only the joining attributes are sent from one site to another and then all of the rows are returned.
This option describes a scenario where only the joining attributes are transmitted from one site to another, but all rows from the joined tables are returned. However, in a semijoin operation, only the required rows from one table (the outer table) are returned, not all rows.

Option B: All of the attributes are sent from one site to another and then only the required rows are returned.
This option suggests that all attributes from one site are transmitted to another, and then only the required rows are returned. However, in a semijoin operation, only the joining attributes are transmitted, not all attributes.

Option C: Only the joining attributes are sent from one site to another and then only the required rows are returned.
This option accurately describes a semijoin operation. In a semijoin, only the joining attributes from one table (the outer table) are sent to another site, where they are used to filter the rows of the other table (the inner table). Only the rows from the inner table that match the joining attributes are returned, reducing the amount of data transferred between sites.

Therefore, in the context of a semijoin operation in a distributed database system, the correct option is Only the joining attributes are sent from one site to another and then only the required rows are returned (Option C).

While replication offers several advantages in a distributed database system, it also comes with certain disadvantages or limitations.

Option A: Reduced network traffic
This option describes a potential advantage of replication rather than a disadvantage. Replication can indeed reduce network traffic by allowing local access to data copies, thereby minimizing the need for data transfer across network links.

Option B: If the database fails at one site, a copy can be located at another site.
This option highlights a benefit of replication in terms of fault tolerance and high availability. Having copies of the database at multiple sites ensures data redundancy and resilience against failures. It does not represent a disadvantage of replication.

Option C: Each site must have the same storage capacity.
This option correctly identifies a disadvantage of replication. In a replication setup, each site hosting a copy of the database must have sufficient storage capacity to accommodate the replicated data. Ensuring uniform storage capacity across all sites can be challenging and may lead to resource constraints or inefficiencies, especially in heterogeneous environments where sites have different storage capabilities or requirements.

Option D: Each transaction may proceed without coordination across the network.
This option describes a characteristic of loosely coupled distributed systems rather than a specific disadvantage of replication. In distributed databases with replication, transactions may indeed proceed independently at each site without requiring immediate coordination across the network. While this decentralization of transaction processing can improve performance and scalability, it also introduces complexities related to maintaining data consistency and isolation.

Therefore, in the context of disadvantages of replication in a distributed database system, the correct option is Each site must have the same storage capacity (Option C).

A distributed database can employ various strategies to manage its data across multiple sites.

Option A: Totally centralized at one location and accessed by many sites
In this strategy, although the database is centralized at one location, it is accessed by multiple sites. This approach may involve having a central server that holds the entire database, and other sites access this central database over a network. While it simplifies data management and ensures data consistency, it can lead to network congestion and single points of failure.

Option B: Partially or totally replicated across sites
Replication involves creating and maintaining copies of data across multiple sites. In a distributed database, data can be partially or entirely replicated across sites to improve data availability, fault tolerance, and performance. Replication allows local access to data, reducing the need for network communication and enhancing responsiveness. However, it requires mechanisms to ensure data consistency among replicas.

Option C: Partitioned into segments at different sites
Partitioning, also known as sharding, involves dividing the database into segments or partitions, with each partition stored at a different site. This strategy aims to distribute data and workload evenly across sites, improving scalability and performance. By partitioning data, queries can be executed locally on the site where the relevant data resides, reducing network overhead and enhancing efficiency.

Option D: All of the above
All the mentioned strategies—centralization, replication, and partitioning—are viable approaches for managing data in a distributed database. Depending on the requirements of the application, a distributed database system may utilize one or a combination of these strategies to achieve its goals, such as improving performance, availability, and fault tolerance.

Therefore, in the context of a distributed database, the correct option is All of the above (Option D).

The evolution of distributed Database Management Systems (DBMS) involves several stages, each representing advancements in architecture and functionality to support distributed data processing.

Option A: Unit of work
The concept of a unit of work represents the earliest stage in the evolution of distributed DBMS. In this stage, transactions are processed as atomic units of work within a single centralized database system. Transactions are executed sequentially, and concurrency control is limited to within the boundaries of a single database.

Option B: Remote unit of work
The stage of remote unit of work builds upon the concept of a unit of work by introducing the capability to execute transactions that involve accessing data located on remote sites. In this stage, transactions may span multiple nodes or sites in a distributed environment, but the processing is still coordinated by a central authority.

Option C: Distributed unit of work
The distributed unit of work stage represents a further advancement where transactions can be processed independently at each participating node or site in a distributed system. Transactions are decomposed into subtransactions, and each subtransaction can be executed autonomously at its respective node. Coordination and synchronization mechanisms are implemented to ensure consistency and isolation across distributed transactions.

Option D: Distributed request
This option does not correspond to a recognized stage in the evolution of distributed DBMS. While distributed requests are integral to distributed database systems, they are typically associated with the execution of transactions or operations rather than representing a distinct evolutionary stage.

Therefore, in the context of the stages in the evolution of distributed DBMS, the correct option is Distributed request (Option D).

With failure transparency in a distributed database system, all actions of a transaction are committed or none of them are committed, ensuring transaction atomicity and consistency even in the event of failures.

Option A: True
This option correctly describes the principle of failure transparency in distributed transactions. Failure transparency guarantees that if a transaction encounters an error or failure at any point during its execution, all the actions performed by the transaction are rolled back or aborted to maintain data consistency and integrity. This ensures that the database remains in a consistent state despite failures and that partial updates or inconsistencies are avoided.

Option B: False
This option contradicts the concept of failure transparency. If transactions were not subject to failure transparency, it would mean that the system allows partial updates or inconsistent states to persist in the database, which could lead to data corruption or integrity violations. In distributed databases, failure transparency is a fundamental requirement to ensure transaction reliability and correctness.

Therefore, in the context of failure transparency in distributed database systems, the correct option is True (Option A).

In a distributed system, each site or node is subject to the same types of failure as in a centralized system, including hardware failures, software failures, network failures, and human errors.

Option A: True
This option correctly states that each site or node in a distributed system can experience various types of failures similar to those encountered in a centralized system. These failures can include hardware failures such as disk crashes or memory errors, software failures such as bugs or crashes in the operating system or application software, network failures such as link failures or packet loss, and human errors such as misconfiguration or accidental data deletion. Dealing with these failures is essential for ensuring the reliability, availability, and fault tolerance of the distributed system.

Option B: False
This option incorrectly suggests that distributed systems are immune to certain types of failures or have different failure characteristics compared to centralized systems. However, distributed systems face many of the same challenges and vulnerabilities as centralized systems, and failure management is a critical aspect of distributed system design and operation.

Therefore, in the context of failures in distributed systems compared to centralized systems, the correct option is True (Option A).

Replication in distributed database systems can utilize either synchronous or asynchronous technologies for data propagation and synchronization. However, asynchronous technologies are more commonly employed in a replicated environment due to their advantages in terms of performance and scalability.

Option A: True
This option correctly states that replication may utilize both synchronous and asynchronous distributed database technologies. Synchronous replication involves immediate data propagation and acknowledgment of updates across all replicas before committing a transaction, ensuring data consistency but potentially introducing latency and performance overhead. Asynchronous replication, on the other hand, allows updates to be propagated to replicas with a delay, enabling faster transaction processing but potentially leading to data inconsistencies or discrepancies between replicas. While both approaches have their benefits and trade-offs, asynchronous technologies are more prevalent in replicated environments due to their ability to provide higher performance and scalability.

Option B: False
This option contradicts the statement provided in the question. It suggests that only synchronous technologies are typical in a replicated environment, which is not accurate. While synchronous replication is suitable for scenarios requiring strict data consistency and integrity, asynchronous replication is more commonly used in replicated environments due to its advantages in terms of performance, scalability, and fault tolerance.

Therefore, in the context of replication technologies in distributed database systems, the correct option is True (Option A).

In pull replication, synchronization is less disruptive compared to other replication methods because updates occur only when needed by each site, rather than being dictated by a central master site.

Option A: True
This option correctly describes the characteristic of pull replication. In pull replication, individual sites or nodes initiate the synchronization process based on their own needs or schedules. When a site requires updates from other nodes, it pulls the necessary data or changes from those nodes. This approach allows each site to control the timing and frequency of synchronization, reducing the potential for disruption to ongoing operations. Pull replication is particularly suitable for distributed environments where network bandwidth or resource constraints may limit the feasibility of continuous or frequent updates from a central master site.

Option B: False
This option contradicts the statement provided in the question. It suggests that synchronization in pull replication is more disruptive or occurs according to a schedule determined by a central master site, which is not accurate. Pull replication is specifically designed to offer flexibility and minimize disruption by allowing individual sites to trigger synchronization as needed, based on local requirements and conditions.

Therefore, in the context of synchronization in pull replication in distributed database systems, the correct option is True (Option A).

In asynchronous replication technology, updates to data items are not immediately applied to all other copies across the network. Instead, updates are propagated with a delay, and inconsistencies between copies may exist temporarily.

Option A: True
This option incorrectly describes the behavior of asynchronous replication. It suggests that updates are immediately applied to all copies of a data item across the network, which is characteristic of synchronous replication rather than asynchronous replication. In synchronous replication, updates are propagated synchronously, ensuring that all copies are kept consistent in real-time.

Option B: False
This option correctly describes the behavior of asynchronous replication. In asynchronous replication, updates to data items are not immediately applied to all copies across the network. Instead, updates are propagated asynchronously with a delay. As a result, temporary inconsistencies or lag may exist between copies until updates are fully propagated to all nodes.

Therefore, in the context of asynchronous replication technology in distributed database systems, the correct option is False (Option B).