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DBMS → Database Architecture 22

What is the primary advantage of connection pooling?
It reuses established database connections reducing overhead of creating new connections for each request
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The query processor in a DBMS consists of which components?
DDL interpreter, DML compiler, and query evaluation engine
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Which architectural pattern does Apache Hadoop use?
Shared-nothing architecture with MapReduce
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What is data sharding in distributed database architecture?
Horizontally partitioning data across multiple database nodes based on a shard key
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The CAP theorem states you can only guarantee at most two of:
Consistency, Availability, Partition Tolerance
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In a Lambda architecture the speed layer is responsible for:
Processing real-time streaming data to provide low-latency approximate results
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Column-store database architecture is better suited for OLAP because:
Storing values of each column contiguously enables high compression and allows reading only required columns reducing I/O for aggregation queries
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What is the purpose of Write-Ahead Logging (WAL)?
To ensure all changes are logged to disk before they are applied enabling recovery after failures
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What is the difference between synchronous and asynchronous replication?
Synchronous waits for replica confirmation before committing; asynchronous commits immediately and replicates later
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What is MVCC (Multi-Version Concurrency Control)?
A concurrency control mechanism that maintains multiple versions of data to allow reads without blocking writes
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What is the purpose of a materialized view?
Materialized views physically store precomputed query results improving performance at the cost of storage and refresh overhead
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In a distributed database the 2PC protocol is used to:
Ensure atomicity of distributed transactions across multiple database nodes
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What is the database-per-service pattern in microservices?
Each microservice owns its private database preventing direct access by other services
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What is the primary architectural difference between OLTP and OLAP systems?
OLTP optimizes for many short transactions with point lookups; OLAP optimizes for complex analytical queries over large datasets
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Which component is responsible for lock management in concurrent transactions?
Lock Manager (part of Concurrency Control Manager)
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What is the SAGA pattern in microservices database architecture?
It manages long-running distributed transactions without using 2PC using a sequence of local transactions with compensating transactions
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What is data partitioning and how does horizontal differ from vertical?
Horizontal partitioning splits rows across multiple partitions; vertical partitioning splits columns across multiple tables
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What is NUMA and how does it affect database architecture?
A memory architecture where processors have different latencies to different memory regions requiring NUMA-aware data placement
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What does event-sourcing architecture store as the primary record?
An immutable sequence of events/changes from which current state can be derived
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The Shared Disk architecture (e.g. Oracle RAC) has which characteristic?
Multiple nodes share the same storage but have separate memory using cache coherency protocols
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What is the role of the catalog manager in DBMS architecture?
Maintains the data dictionary containing metadata about all database objects
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What is join pushdown in federated query systems?
Sending the join operation to a remote data source rather than fetching both tables to the coordinator allowing the remote DBMS to handle the join natively
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DBMS → Data Models 18

In the object-oriented data model what is encapsulation?
Bundling data (attributes) and methods that operate on that data within an object hiding internal implementation details
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The document data model (MongoDB) is best suited for which scenario?
Storing hierarchical semi-structured data where document structure can vary
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What is the semantic data model and its primary purpose?
A high-level conceptual model capturing the meaning of data to bridge the gap between the real world and DBMS implementation
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In the relational data model referential integrity is enforced by which constraint?
Foreign key constraint
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The key-value data model (Redis) has which fundamental characteristic?
It stores data as opaque values indexed by unique keys with very simple query capability
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What is the primary advantage of the graph data model over relational for highly connected data?
Graph databases natively model and traverse relationships without expensive JOIN operations making relationship-heavy queries much faster
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In wide-column store data model (Cassandra/HBase) what distinguishes it from relational?
Rows can have different columns grouped into families; optimized for distributed storage and time-series data
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What is the XML data model and what concept does it use?
It represents data as a hierarchical tree structure using elements, attributes, and text nodes defined by DTD or XML Schema
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What is a surrogate key and why is it preferred over natural keys?
A surrogate key is a system-generated artificial identifier (like auto-increment ID) with no business meaning preferred because natural keys can change and may be long/complex
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The star schema data model used in data warehouses consists of:
A central fact table surrounded by denormalized dimension tables
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What is a snowflake schema and how does it differ from a star schema?
Snowflake schema normalizes dimension tables into multiple related tables reducing redundancy but requiring more JOINs than star schema
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What does BASE stand for and how does it contrast with ACID?
BASE: Basically Available, Soft state, Eventual consistency - trades strict consistency for availability and partition tolerance
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What is the fundamental difference between conceptual, logical, and physical data models?
Conceptual: high-level business concepts; logical: entities, attributes, keys, DBMS-agnostic; physical: exact DBMS-specific implementation (tables, indexes, partitions)
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Which data model best supports multi-valued attributes natively without normalization?
Object-oriented model and document model
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What is the purpose of a junction table (bridge or associative entity)?
To resolve many-to-many relationships between two entities into two one-to-many relationships in the relational model
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What is the temporal data model and what problem does it solve?
A model that tracks time-varying data recording history with valid-time (when true in reality) and transaction-time (when recorded in DB) dimensions
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What is the entity-attribute-value (EAV) data models main disadvantage?
Data retrieval requires complex pivoting, referential integrity is difficult to enforce, and performance is poor for queries accessing multiple attributes
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In property graph models (Neo4j) what can both nodes and edges have?
Both nodes and edges can have key-value property maps and labels/types
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