In database systems and operating systems, what do we mean by a deadlock between processes or transactions?

Introduction / Context:
Deadlocks are a classic problem in operating systems and database systems. They occur when multiple processes or transactions compete for resources such as locks, and a circular waiting relationship prevents all of them from making progress. Understanding deadlocks is important for designing safe locking strategies, transaction management, and concurrency control. This question asks for a clear definition of deadlock in the context of processes or transactions.

Given Data / Assumptions:

• Multiple processes or database transactions may need exclusive access to resources such as files, tables, or rows.
• Locks or similar mechanisms are used to enforce mutual exclusion on these resources.
• Processes may acquire resources one at a time while holding others.
• There is a possibility of circular waiting where each participant holds a resource that the next one needs.

Concept / Approach:
A deadlock occurs when a set of processes or transactions are in a state where each is waiting for an event that only another process in the same set can cause. In a simple scenario, process A holds resource X and waits for resource Y, while process B holds resource Y and waits for resource X. Since neither can release what the other needs until it acquires its own needed resource, both remain blocked forever unless external intervention breaks the cycle. In database systems, deadlocks often involve row or table locks. Operating systems and database managers implement detection, prevention, or avoidance strategies to handle such situations.

Step-by-Step Solution:
Step 1: Identify the resources that processes or transactions are competing for, such as locks on data items.Step 2: Observe that each participant has acquired some resources and is now waiting for additional ones.Step 3: Check whether there is a cycle in the wait for graph, where the resource wait dependencies form a closed loop.Step 4: If such a cycle exists and no participant can proceed without acquiring further resources from the cycle, the system is in deadlock.Step 5: Recognise that external action, such as aborting a transaction or preempting a resource, is needed to break the deadlock.

Verification / Alternative check:
Many database systems provide logs or views that show deadlock errors, often including a wait for graph. These records illustrate that each transaction is waiting for locks held by another. In operating systems, textbooks define deadlock in terms of four conditions: mutual exclusion, hold and wait, no preemption, and circular wait. When all these conditions hold simultaneously, a deadlock can occur. Comparing the technical definition with observed behaviour in real systems confirms the described concept.

Why Other Options Are Wrong:
Option B describes a process running quickly, which is not a deadlock; in fact, that process makes progress. Option C refers to context switching, which is normal behaviour in multitasking and does not imply circular waiting. Option D talks about temporary delays from slow disk reads, which are performance issues but not necessarily deadlocks because progress resumes once the operation completes. These situations do not involve the circular waiting condition that defines deadlock.

Common Pitfalls:
A common pitfall is confusing deadlock with general performance problems or simple contention. High load can cause delays without true deadlock. Another mistake is designing locking schemes that acquire resources in inconsistent orders across different parts of the application, which increases the risk of circular waits. Best practices include acquiring locks in a consistent global order, using timeouts, and relying on built in deadlock detection and retry mechanisms in database systems. Understanding the definition of deadlock helps developers recognise and mitigate these issues in concurrent applications.

Final Answer:
Correct answer: A situation where two or more processes or transactions are each waiting for resources held by the others so that none of them can proceed