Both SQL Server Audit and Extended Events can capture the same underlying engine events. That overlap is exactly why teams pick the wrong one — the question isn't "which tool can do this," it's "which tool is built for the purpose I actually have."
What SQL Server Audit Is Actually For
SQL Server Audit is purpose-built for compliance: it produces a tamper-evident, structured audit trail tied to specific actions (logins, permission changes, schema modifications, data access) and writes that trail to a file, the Windows Security log, or the Windows Application log. Audit specifications are declarative — you define what to capture using predefined audit action groups rather than constructing event logic by hand — which makes the resulting configuration straightforward to document and explain to an auditor. That's the real differentiator: Audit is designed to be defensible evidence, not just diagnostic data.
What Extended Events Is Actually For
Extended Events is a lightweight, highly flexible diagnostic and troubleshooting framework that can capture a far broader range of engine events than Audit — query execution details, wait statistics, lock escalation, deadlock graphs, plan compilation. It's the tool for "why is this query slow" and "what caused this deadlock," not for "prove that no unauthorized permission changes occurred last quarter." Extended Events sessions are also more configurable in terms of filtering and target types, which makes them well suited to narrow, temporary diagnostic capture without the overhead of logging everything continuously.
Performance Overhead: Smaller Than the Old Reputation Suggests, But Not Zero
Both tools are built on the lightweight Extended Events engine internally — Audit is implemented on top of it — so neither carries the heavy overhead of legacy SQL Trace. That said, overhead scales with what you capture and how granularly you filter. A narrowly scoped Audit specification capturing only permission and login changes has negligible impact. A broad Extended Events session capturing every statement completion on a high-throughput OLTP system will show measurably on CPU and I/O. Scope what you capture to what you actually need to answer — for either tool.
Storage Targets Matter for the Compliance Use Case
Where Audit output lands matters for whether it's actually defensible. A file target the SQL Server service account can modify isn't strong evidence; writing audit logs to a separate, access-restricted location — or to the Windows Security log, which has its own access controls — is what makes the audit trail meaningful rather than theoretical. This is one of the most common gaps found in security assessments: Audit is technically enabled, but configured in a way that wouldn't survive a real compliance review.
The Practical Answer: Use Both, for Different Jobs
Configure SQL Server Audit for the events that need a defensible, continuous compliance record — permission changes, login activity, schema modifications on regulated data. Use Extended Events for targeted, often temporary diagnostic capture when troubleshooting a specific performance or behavioral issue. Trying to make one tool do both jobs usually means either an under-built compliance trail or an over-built, performance-impacting diagnostic session running permanently in production.
If you're not sure whether your current Audit configuration would hold up under a real compliance review, request a SQL Server Security Assessment.