Explain the internal working of SQLite's B-tree storage structure?

Every table and index in SQLite is stored as a separate B-tree within the single database file — a balanced tree structure where each node is one fixed-size page (typically 4096 bytes), organized so that lookups, insertions, and range scans all stay efficient even as the table grows large.

flowchart TD
    A[Root page] --> B[Interior page]
    A --> C[Interior page]
    B --> D[Leaf page: rows 1-50]
    B --> E[Leaf page: rows 51-100]
    C --> F[Leaf page: rows 101-150]

Table B-trees are keyed by rowid and store the actual row data in their leaf pages; index B-trees are keyed by the indexed column's value and store a reference back to the corresponding rowid, which is then used to fetch the full row from the table's own B-tree. A lookup by primary key (rowid) is a single B-tree traversal; a lookup via a secondary index requires first traversing the index's B-tree, then a second traversal into the table's B-tree to fetch the actual row — which is why a "covering index" (one that includes every column a query needs) can skip that second traversal entirely.

Invest now in Acorns!!! 🚀
Join Acorns and get your $5 bonus!

Acorns is a micro-investing app that automatically invests your "spare change" from daily purchases into diversified, expert-built portfolios of ETFs. It is designed for beginners, allowing you to start investing with as little as $5. The service automates saving and investing. Disclosure: I may receive a referral bonus.

Invest now!!! Get Free equity stock (US, UK only)!

Use Robinhood app to invest in stocks. It is safe and secure. Use the Referral link to claim your free stock when you sign up!.

The Robinhood app makes it easy to trade stocks, crypto and more.

Webull! Receive free stock by signing up using the link: Webull signup.