We had a performance issue that we solved by restarting the sql server service. That's obviously not the way we want to continue handling our performance issues.
When a sql server performs better after restart the probable causes to me are
- wrong cached query plans
- memory pressure
To rule out wrong query plans being cached query plans we first dropped the query cache with
but the problem persisted.
I am still not sure about memory pressure. Page life expectancy goes down during the bad performance period to 50s. But cache hit ratio is 100%.
Are the numbers suggesting memory pressure here or are there other possible reasons?
I put a beautiful red line where we restarted the sql server service.
At the time of the issue we did not have more requests than usual.