Master 131 critical interview questions from Core C# Fundamentals → Advanced CLR Memory & GC → Deep SQL Server Tuning → Cloud Security & Distributed Microservices. Designed with simple analogies, elevator pitches, and live active-recall flashcards.
Focus heavily on the questions interviewers use to separate 10-YOE candidates from juniors:
| Isolation Level | Dirty Reads | Non-Repeatable | Phantom Reads | How it Works |
|---|---|---|---|---|
| Read Uncommitted | ❌ Yes (Risky) | ❌ Yes | ❌ Yes | Ignores shared locks (`NOLOCK`). |
| Read Committed (Default) | ✅ Prevented | ❌ Yes | ❌ Yes | Acquires & releases shared locks per statement. |
| RCSI (Recommended) | ✅ Prevented | ❌ Yes | ❌ Yes | Row versioning in TempDB. Readers never block writers! |
| Serializable | ✅ Prevented | ✅ Prevented | ✅ Prevented | Key-range locks. Maximum safety, high lock contention. |
| Area | Threshold | Key Nuance |
|---|---|---|
| Gen 0 | Short-lived objects | Sub-millisecond collection. Allocated in ephemeral segment. |
| Gen 1 | Medium-lived (buffer) | Acts as a buffer between Gen 0 and long-lived Gen 2. |
| Gen 2 | Long-lived (Singletons) | Full GC. Expensive pause. Triggered when Gen 2 or LOH is full. |
| LOH | >= 85,000 bytes | Not compacted by default (causes fragmentation). Use `ArrayPool |