Like the title says, I have a stored procedure that suddenly started running very slowly. Previously it took about 5 seconds to execute, now it is taking seven minutes or more. This seems to have started when I altered the procedure, but the change I made should not have impacted the performance, as all I did was change the alias on two columns being returned. I'm not sure if altering the procedure actually caused this, however, because a similar procedure that also used to be very fast is having the same issues.

I tried updating statistics on the relevant tables and it did not help. I had this same problem last week and was able to fix it by doing that, but now it's a no go. I also tried using with recompile to no avail and deleted the procedure then re-added it.

This is the line that is taking much longer than before:

select PK_ShipDataSubsystemConfigID
,timestamp
,cast((
        select top 1 Longitude
        from [RemoteServer].[dbo].[Ships].LocationAttributes la
        inner join [RemoteServer].[dbo].[Ships].Locations l on l.ShipLocationId = la.ShipLocationId
        where l.SampleDateTime <= timestamp
            and l.SampleDateTime <= @ToDT
            and ShipId = @ShipId
        order by SampleDateTime desc
        ) as varchar(20)) as Longitude
,'Vessel Position Lng'
from FuelCalc
inner join ShipDataSubsystemConfig s on s.PK_ShipDataSubsystemConfigID =       FuelCalc.FK_ShipDataSubsystemConfigId
where timestamp > @FromDT
and timestamp < @ToDT
and FuelCalc.FK_ShipId = @ShipId
order by timestamp desc

Running the inner select by itself now takes at least 2 seconds, so I can understand why the whole procedure is taking so long. I am wondering if it has something to do with it being a call to a linked server. I tried creating a view joining the Locations and LocationAttributes tables to see if it made a difference, but it did not.

Any ideas? I have asked around with my coworkers and they are just saying I need to write a more efficient query (which may be true) but I really don't think that's causing my particular problem seeing as it was working fine until suddenly it wasn't. I looked at the execution plan but all it says is that the remote query is taking 100% of the time, but doesn't show the plan at more detail than that.