In the days before it was possible to get query statistics from the Performance Schema, the slow query log was the main source of information to find queries that are candidates for optimization. Even today, the slow query log should not be completely dismissed.
The slow query log has three main advantages over the statement digest information in the Performance Schema. The logged queries are persisted, so you can review the information after MySQL has been restarted, the queries are logged with timestamps, and the actual queries are logged. For these reasons, the ...
