Finding what to fix.
WHY IT IS THE PRIMARY TOOL
It records exactly what was slow, with figures.
WHAT EACH ENTRY CONTAINS
The query Time taken Lock time Rows examined Rows sent
WHAT THE MOST USEFUL RATIO IS
Rows examined against rows sent.
WHY
A large gap means the database read far more than it returned.
WHAT TO DO WITH A RAW LOG
Summarise it.
WHY
The same query appears thousands of times with different values.
WHAT SUMMARY TOOLS PROVIDE
Queries grouped by shape, ranked by total time.
WHY TOTAL TIME RATHER THAN SLOWEST
A query taking a moment, run constantly, may cost more than one slow report.
WHAT TO FIX FIRST
Whatever consumes the most total time.
WHAT TO LOOK AT NEXT
Queries examining the most rows.
WHAT TO DO FOR EACH
Read the execution plan Identify the missing or unusable index Test the change on a copy
WHAT TO MEASURE AFTERWARDS
The same summary, comparing.
WHAT TO SET UP
Regular review, rather than only during incidents.
WHY
It catches degradation before it becomes an outage.
WHAT TO ROTATE
The log itself, which grows.
