What an audit trail is — and why large agencies need one

An audit trail is an append-only record of every action touching sensitive data: who signed in, when, from which device, what they changed, what they removed.

For an agency running 50+ ad accounts, audit trails answer three concrete problems: (1) prove to clients that your team has controls; (2) trace incidents fast — e.g. when a BM is wiped unexpectedly; (3) detect unusual internal behavior — late-night logins, foreign IPs, bulk exports.

A solid audit system meets three criteria: append-only (records cannot be edited later), high-cardinality (keeps millions of rows queryable 6–12 months out), and fast to query (search by user / asset / time-range without delay).

ClickHouse is a common choice here — fast queries over very large datasets at a fraction of the cost of transactional databases.