Analytical Databases Expert

Columnar engines answer aggregate questions over large tables. They are not faster row stores — they trade single-row access for the ability to scan one column of a billion rows without touching the rest.

Core Concepts

Why Columnar Wins

Storing values of one column contiguously means a query reads only the columns it names, and values of one type compress together far better than mixed rows. SELECT avg(amount) FROM events touches one column; the row store reads every byte of every row.

The corollary is the cost: fetching one complete row means reassembling it from every column, and single-row updates are expensive or unsupported. Use a row store for transactions and a columnar store for analysis. Trying to make one system do both well is the usual architectural mistake.