Have you considered using snapshot isolation? Enabling read_committed_snapshot in the database will cause all reads (selects) to be lock free:
alter database [...] set read_committed_snapshot on;
No application changes. Some semantics change under snapshot and your application may react weirdly, but that is the exception not the norm. The vast majority of applications don't notice any difference, they just get a free performance boost.
Anyway, I though to answer also the original question: how to detect (and possibly kill) a long running query. Actually, the engine already does that for you. There is an event raised when a threshold is passed: Blocked Process Report Event Class. The threshold is configured via the blocked process threshold Option. Any trace event can be turned into an Event Notification and event notifications can activate procedures. Connect the dots and you have on-demand activated code that runs when the engine detects a query that has crossed an execution time threshold. No polling, no monitoring. Note though that the notification is asynchronous, by the time you process it the query may had completed so that has to be taken into account.
Here is an example:
use msdb;
go
create queue blocked_process_report_queue;
go
create service blocked_process_report_service
on queue blocked_process_report_queue
([http://schemas.microsoft.com/SQL/Notifications/PostEventNotification]);
create event notification blocked_process_report_notification
on server
for BLOCKED_PROCESS_REPORT
to service N'blocked_process_report_service',
N'current database';
go
sp_configure 'show advanced options', 1 ;
GO
RECONFIGURE ;
GO
sp_configure 'blocked process threshold', 20 ;
GO
RECONFIGURE ;
Now in a new query set up a WAITFOR expecting a notification:
use msdb;
waitfor(
receive cast(message_body as xml), *
from blocked_process_report_queue);
And go ahead and cause some blockage. I used a process that created a table and didn't commit, and from another query windows I tried to select from the table. In 20 seconds (my configured threshold above) I got the blocking report:
<blocked-process-report>
<blocked-process>
<process id="process1b5a24ca8" ...>
<executionStack>
<frame line="1" stmtstart="-1"... />
</executionStack>
<inputbuf>
select * from t </inputbuf>
</process>
</blocked-process>
<blocking-process>
<process status="sleeping" spid="51" ...>
<executionStack />
<inputbuf>
begin transaction
create table t (a int) </inputbuf>
</process>
</blocking-process>
</blocked-process-report>
I'll leave the task of wrapping this up into an automated process as an exercise to the reader. And yes, the queue/service/activated procedure must be in [msdb].
“I'm wondering if there is some odd setting that is killing older, not active connections?” – short answer is no.
This is probably network issue, or SQL Server being under big performance impact or DNS or something similar.
Is your application on the same machine as SQL Server ? Do you have any other issues? Can you run SQL Server from Enterprise manager w/o issues?
Best Answer
Do you know exactly what the INSERT statement is and what line of EF code generates it? Just wrap whatever calls that around some logging code and log all the SQL to a text file (preferably using log4net, nlog, ETW etc.
Just wrap the code that calls the insert code with a call to set and unset the delegate described here.
e.g.
Honestly, if you can deal with a slight slowdown in performance, and have the disk space just log everything. I log all the SQL in my Always Encrypted Sample app.
Assuming your INSERTS are wrapped around transactions, you should be able to see that instantly with this. Make sure your logging has timestamps so you can see how long the transaction remains open for.