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Java & Spring Boot

1.Java Memory Model Foundations: Visibility, Ordering, and Safe Publication
2.ConcurrentHashMap Internals: Coordinating Updates Without One Global Lock
3.Spring Transaction Boundaries: Where to Commit and When to Split
4.JVM Memory Errors: Diagnose Heap Exhaustion, StackOverflow, and Leaks
5.Java Thread Dumps: Find Deadlocks, Starvation, and Lock Contention
6.Java equals and hashCode: Fix Broken HashMap and HashSet Lookups
7.Java Exception Debugging: Trace the Root Cause and Fix the Boundary
8.Advanced Java and Spring: Runtime, Concurrency, Proxies, and Reactive Failure Modes
9.Java Appointment Times: Resolve DST Gaps and Overlaps Explicitly
10.Java deadlines: spend one budget across every stage
11.Java class-loader retention: why an undeployed app can remain in memory

Python & Async APIs

1.Python Data Model Foundations: Objects, Types, and Reliable Boundaries
2.Python Collections: Lists, Tuples, Sets, and Map/Reduce Trade-offs
3.Python Error Debugging: Tracebacks, Root Causes, and Safe Fixes
4.FastAPI Async Patterns: When to Use Background Tasks vs Real Concurrency
5.FastAPI Backpressure: Protecting Your Service from Unbounded Fan-Out
6.Async Python Cancellation and Timeouts: Stop Work Without Leaking It
7.Debugging Flaky Python Tests: Time, State, Concurrency, and Isolation
8.Python Async Runtime Advanced: GIL, ASGI Lifecycles, and Safe Concurrency
9.Python Runtime Advanced: Native Memory, ASGI Lifecycles, and Worker Failure
10.Python Event Times: Normalize Offsets Without Losing Elapsed Time
11.Python queues: bound waiting work and own its completion
12.Python TaskGroups: make sibling failure and cleanup part of the design

Security & Authentication

1.Authentication Foundations: Sessions, Cookies, and Trust Boundaries
2.Security Boundaries: Object Authorization, Input Validation, and Secret Handling
3.Tenant authorization: carry trusted scope into every lookup
4.CSRF defenses: reason from browser credential attachment, not CORS

Distributed Systems

1.Distributed Systems Foundations: Consistency, Retries, and Delivery Semantics
2.Kafka Consumer Groups: Architecture & Common Pitfalls
3.Idempotency and the Transactional Outbox: Making Retries Safe
4.Distributed Systems Advanced: Rebalancing, Sagas, Consensus, and Trace Context
5.Consensus and Observability Advanced: Quorums, Split Brain, and Trace Context
6.Event-Time Windows: Watermarks, Late Data, and Correctable Results
7.Fencing tokens: reject workers whose lease has expired
8.Causal order: what a logical clock can and cannot tell you

DevOps & Delivery

1.DevOps Foundations: Reproducible Builds and Artifact Promotion
2.DevOps Foundations: Safe Changes, Health Signals, and Rollback Boundaries
3.Docker Multi-Stage Builds: Optimization Patterns for Production
4.Production Observability: Signals, Service Objectives, and Useful Alerts
5.Reliable CI Pipelines: Fast Feedback Without Hiding Failures
6.Delivery Engineering Advanced: Build Caches, Runner Isolation, and Safe Releases
7.Release Safety Advanced: State, Schema Compatibility, and Artifact Trust
8.Incident Timelines: Separate Event Time, Receipt Time, and Clock Evidence
9.Scheduled jobs: separate a logical run from its attempts
10.CI workload identity: replace copied cloud keys with scoped claims

Databases & SQL

1.Relational Databases and SQL Foundations: Model the Invariant First
2.PostgreSQL MVCC and Indexes: Reads, Vacuum, and Query Plans
3.MySQL InnoDB: Transactions, Indexes, and Reading EXPLAIN
4.Oracle SQL: Analytic Functions, Execution Plans, and Bind Variables
5.SQL Query Recipes: Joins, Grouping, Window Functions, and Safe Pagination
6.Top-N and Third-Highest Salary Queries in PostgreSQL, MySQL, and Oracle
7.Stored Functions, Procedures, and Triggers: Put Logic in the Right Layer
8.Database Locks and Isolation: Diagnose Blocking, Deadlocks, and Retries
9.Fix Slow SQL: N+1 Queries, Missing Indexes, and Bad Cardinality Estimates
10.Database Internals Advanced: MVCC Anomalies, Cost Models, Sharding, and Storage Engines
11.SQL Event Gaps: LAG, Stable Ordering, and Explicit Window Frames
12.SQL keyset pagination: continue an order without promising a snapshot
13.PostgreSQL concurrent indexes: reason about locks, retries, and invalid states

Unix & Linux

1.Unix Foundations: File Permissions, Ownership, and Descriptors
2.grep, sed, and awk: Reliable Text Search and Small Stream Programs
3.Shell Script Debugging: Trace Failures, Preserve Exit Codes, and Fix Safely
4.TCP, UDP, ss, netstat, and tcpdump: A Layered Network Debugging Guide
5.pipefail, Signals, and Unix Process Management
6.Unix Signals and Child Processes: What Your Service Must Clean Up
7.DNS Troubleshooting: Trace Name Resolution Before Blaming the Network
8.Linux Disk Full Errors: Blocks, Inodes, Deleted Files, and Safe Cleanup
9.Linux Under Load: Epoll, File Descriptors, OOM, TCP Queues, and VFS
10.Unix Log Sorting: Normalize Offset Timestamps Before Ordering Events
11.Unix file publication: replace names without exposing partial bytes
12.Unix process inheritance: environment variables and file descriptors

HTTP & APIs

1.HTTP Foundations: Methods, Status Codes, and Representation Boundaries
2.Reliable API Clients: Pagination, Conditional Requests, and Retry Budgets
3.HTTP conditional writes: detect an edit based on stale state
4.HTTP range requests: resume transfers without stitching different files

Kubernetes & Platform

1.Kubernetes Foundations: Pods, Workloads, and Declarative State
2.Kubernetes Foundations: Services, Configuration, and Least-Privilege Access
3.Kubernetes Foundations: Objects, Controllers, and Reconciliation
4.Kubernetes Rollouts: Readiness, Health Checks, and Safe Deployments
5.Kubernetes Requests, Limits, and Autoscaling: A Practical Capacity Model
6.Kubernetes Advanced Operations: Packet Paths, Rollouts, DNS, and Operators
7.Kubernetes CronJobs: Timezones, Missed Starts, and Duplicate Work
8.Kubernetes disruption budgets: protect capacity, not every failure
9.Kubernetes finalizers: deletion is a protocol, not a cleanup callback

TypeScript & Node.js

1.TypeScript Foundations: Narrow Unknown Data Before Trusting It
2.Node.js Foundations: Event Loop Work, Backpressure, and Cancellation
3.TypeScript results: distinguish absence, invalid input, and dependency failure
4.TypeScript async iterators: connect pull-based demand to resource cleanup

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databases

10 min

Top-N and Third-Highest Salary Queries in PostgreSQL, MySQL, and Oracle

Choose between distinct salary ranking, row ranking, and pagination syntax while handling ties and NULLs explicitly.

Q&A

How do you find the third-highest distinct salary in SQL?

Use DENSE_RANK for distinct values and state whether you want salary values or employee rows.

Read the concise answer

Filter out NULL salaries, compute DENSE_RANK() OVER (ORDER BY salary DESC), then select rank 3. DENSE_RANK treats equal salaries as the same rank. PostgreSQL, MySQL 8+, and Oracle support this window-function approach; if you instead mean the third row, use ROW_NUMBER with a deterministic tie-breaker.

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