Causes of data unavailability in database systems: Which option best summarizes typical sources of downtime or inaccessibility?

Introduction / Context:
Data availability is a core nonfunctional requirement. Unavailability can arise from technical faults, human error, planned maintenance, or data quality issues that prevent safe usage. Recognizing the breadth of causes helps teams build resilient architectures and operations.

Given Data / Assumptions:

• We consider both technical outages and logical unavailability (data is present but not trustworthy).
• Maintenance windows can deliberately make data temporarily inaccessible.
• Server issues can include hardware, OS, DBMS, or network failures.

Concept / Approach:

“Availability” means the system can serve correct, timely data. If data is corrupted or inaccurate, it may be unavailable for business use even if the server is up. Similarly, planned activities (patching, schema changes, backups) can require downtime. Server or infrastructure problems obviously cause outright inaccessibility.

Step-by-Step Solution:

Verification / Alternative check:

Service-level incident reports often classify incidents across these buckets; capacity planning and maintenance calendars confirm planned outages as contributors to downtime.

Why Other Options Are Wrong:

Each single-cause option is incomplete; availability engineering must address all sources.

Common Pitfalls:

Focusing solely on hardware redundancy while ignoring data quality and change management; skipping chaos testing or backup restore drills.

Final Answer:

All of the above.