Delta Lake & Lakehouse — Quick Recall
🗺️ Memory Map
How to use this file:
- ⚡ = Must remember (95% chance of being asked)
- 🔑 = Key concept (core understanding needed)
- ⚠️ = Common trap (interviewers love to test this)
- 🧠 = Memory Map (mnemonic/acronym — memorize this!)
- 📝 = One-liner (flash-card style — cover answer, test yourself)
🧠 MASTER MEMORY MAP — Day 1
🧠 DELTA LAKE = "ACTS on your Data Lake"
DELTA LAKE"ACTS on your Data Lake"
AACID transactions (Atomicity, Consistency, Isolation, Durability)
CCheckpoints (summary every 10 commits)
TTransaction log (_delta_log/ folder = the brain)
SSchema enforcement (rejects bad data)
File Performance = "OVZ→LC" (Old Way → New Way)
OOPTIMIZE (compacts small files into big files)
VVACUUM (deletes old unused files)
ZZ-ORDER (sorts data for fast lookups — OLD way)
→
LLiquid Clustering (REPLACES partitioning + Z-ORDER — NEW way)
CClustering keys (the columns you cluster by)
Time Travel = "VTA"
VVersion number (VERSION AS OF 5)
TTimestamp (TIMESTAMP AS OF '2026-03-20')
AAction to recover (RESTORE TABLE ... TO VERSION AS OF)
Lakehouse = "Lake + Warehouse = Best of Both"
Lake→cheap storage, any format, schema-on-read
Warehouse→ACID, SQL, schema enforcement, fast queries
Lakehouse→all of the above on ONE platform
SECTION 1: DELTA LAKE INTERNALS
🧠 Memory Map: Transaction Log
_delta_log/ = "The BRAIN of Delta Lake"
_delta_log/ = "The BRAIN of Delta Lake"
JSON files = individual commits (diary entries)
Checkpoint = summary every 10 commits (monthly bank statement)
_last_checkpoint = pointer to latest summary
Remember: "JC-L" = JSON → Checkpoint → Last_checkpoint
⚡ MUST KNOW DIRECT QUESTIONS (Cover the answer, test yourself!)
**📝 Q1: What is Delt