42443 occurrence(s) of I/O requests taking longer than 15 seconds to complete
One thing that I don't understand is error got logged only after restarting the web application and then when same UPDATE query was run, it ran fine without waiting on I/O.
[quote]Could outdated statistics be the reason behind I/O latency?
It looks like your disk subsystem is having frequent problems keeping up with the workload being thrown at it. Outdated statistics are not necessarily a cause of that but they can contribute to the problem. If some statistics are out of date and the query optimizer is using sub-optimal execution plans because of them then the database engine may be working harder than it should have to in order to retrieve results to satisfy a query. When is the last time you ran index and stats maintenance routines on your databases? Adding index and stats maintenance to an already overloaded system needs to be done carefully.
I would also recommend you check the disk subsystem for overall health including running CHECKDB on your databases (PS which also need to be done at a time chosen carefully on an already overloaded system).
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