StackScholar

Data

LSM Tree

Writes buffer in a memtable and flush as immutable sorted files, merged by background compaction.

Why interviewers ask about it

Sequential writes make it excellent for high ingest; reads must check several files, so Bloom filters are essential. Compaction causes the p99 spikes that page you at 3 a.m.

Related terms

B+ Tree

A balanced tree with all data in the leaves and high fan-out, so a billion rows is only four levels deep.

Bloom Filter

A probabilistic set that answers 'definitely not present' or 'possibly present', with no false negatives.

This term is part of the free System Design interview preparation module - browse the full glossary for every definition.