Putting It All Together

You've built every piece:

• Probabilistic levels (lesson 1)
• Multi-level structure (2)
• Search (3)
• Insert (4)
• Delete (5)
• Range queries (6)
• Concurrent considerations (7)

Where you'll see skip lists in production:

• Redis sorted sets (ZSET) — implemented as skip list + hash map
• LevelDB / RocksDB — memtable is a skip list (now SkipListRep)
• Java ConcurrentSkipListMap — replacement for synchronized TreeMap
• Apache Cassandra — Memtable
• MongoDB WiredTiger — has skip-list option
• Coq, Agda, Idris — implementations in proof systems for sorted maps

Compared to alternatives:

• B-tree: better cache locality, more complex code
• Red-black tree: tighter memory, harder concurrency
• Hash map: O(1) point lookups but no ordering

Skip list is the sweet spot for ordered concurrent maps in moderate-size data.