Successful login auditing sounds simple: record every connection so security can reconstruct access. Enabling it in the SQL Server error log can instead generate large volumes of repetitive messages, accelerate log cycling, and bury the failures and engine events operators need during an incident. The question is not whether successful logins matter, but which mechanism preserves the required evidence without damaging its usefulness.
Why it matters in production
The design begins with a specific requirement. Teams should define which principals, databases, applications, source hosts, times, and outcomes matter; how quickly the data must be searchable; how long it is retained; who can alter it; and who reviews it. A compliance statement that says only 'log all access' is not yet an operational specification.
SQL Server Audit, Extended Events, the error log, and logon triggers have different strengths and risks. Audit provides structured security records and target controls. Extended Events allows focused technical capture. The error log is convenient but noisy. Logon triggers execute in the connection path and can create availability problems if designed poorly. Selection should follow evidence and performance needs.
Pilot the chosen method under real connection churn. Measure event rate, storage, write overhead, rollover, forwarding delay, query performance, and alert quality. Exclude known health checks only when their identity and behavior are stable, and preserve enough context to connect a login to later actions. Protect the collection path from the same administrators whose activity may need review.
Practical takeaway
The practical takeaway is that more audit volume can produce less visibility. Put successful-login evidence in a structured, controlled channel, filter it according to an explicit requirement, and test retention and investigation workflows. The goal is not to create the largest log; it is to answer who connected, from where, and what happened next when the answer matters.