Author Archives: Stanislav_Panteleev

Designing a high-availability (HA) database system means ensuring the database remains operational with minimal downtime, even in the face of hardware failures, software bugs, or network issues. Here’s how you can approach the design, step by step: ✅ 1. Set … Continue reading →

Understanding the query execution plan (via EXPLAIN) is key to becoming a query performance master. Let’s break it down step by step. 🧠 What Is a Query Execution Plan? A query execution plan is a step-by-step blueprint of how the … Continue reading →

🧠 What Is a Database Optimizer? A database optimizer is a component of a database engine that takes your SQL query and figures out the best plan to execute it. It doesn’t just run the query directly — instead, it … Continue reading →

📘 What is Write-Ahead Logging (WAL)? Write-Ahead Logging is a safety mechanism used by databases to protect your data from being lost or corrupted. 💡 The key idea:Write changes to a log before applying them to the actual database. 🧠 … Continue reading →

🧠 What is the CAP Theorem? The CAP theorem is a rule that says a distributed system (like a NoSQL database spread over many servers) can only guarantee 2 out of 3 things at the same time: C = ConsistencyA … Continue reading →

🧪 ACID — A Super Rule for Databases Think of a database like a notebook where important things are written down: money transfers, orders, messages, etc. We want to make sure: The writing is correct It doesn’t get messed up … Continue reading →

Replication lag is the delay between when a change occurs on the primary database and when that same change is visible on a replica. 🔍 What Does That Mean? Imagine this sequence: A user updates their profile in the primary … Continue reading →

A read replica is a read-only copy of a database that stays in sync with the primary (writeable) database. It is updated asynchronously — meaning changes in the primary DB are eventually propagated to the replica. 🧠 What Is a … Continue reading →

Tracking changes in a table — known as auditing — is essential for data integrity, compliance, and debugging. There are several techniques, depending on how deep and automated you want the auditing to be. ✅ Common Methods to Track Changes … Continue reading →

An index-only scan is a performance optimization used by relational databases (like PostgreSQL, MySQL, Oracle) where a query is satisfied entirely by reading an index, without accessing the table (heap) at all. ✅ What Is an Index-Only Scan? In a … Continue reading →