As part of another question (https://dba.stackexchange.com/questions/54171/sql-server-2012-performance-issues-maybe-due-to-linked-server) I've identified a CPU spike to be directly related to a spike in Bytes Received, which leads me to believe it is likely due to the link server.
THE ENVIRONMENT
2 servers, one server accesses a database on the first via a linked server, for nice diagram, please see https://dba.stackexchange.com/questions/54171/sql-server-2012-performance-issues-maybe-due-to-linked-server
CPU spike directly related to Bytes Received Spike
QUESTION How to find which queries could be causing it??
TYPES OF QUERIES WE RUN
I've went through all our stored procedures, and they are optimized. Here are the types of linked server access that we do:
select one value from remote table
select @userid = userid from FBGC.FBGCommon.dbo.players where playerid = @playerid
execute stored procedure that returns result set of max few hundred rows
exec FBGC.Fbgcommon.dbo.qPlayersFriends @PlayerID
execute stored procedure that returns one value
exec @HasEnoughCredits = FBGC.FBGCommon.dbo.qDoesPlayerHaveEnoughCredits @PlayerID, @Cost
delete a few rows from remove table
delete from FBGC.FBGCommon.dbo.InactivePlayersToBeWarned where PlayerID = @AccountOwnerPlayerID
Update one row in remote table, or add one row to remote table
update FBGC.FBGCommon.dbo.users set XP = XP + @XPForTitle where userid = @userid
insert into FBGC.FBGCommon.dbo.UserXPHistory (userid, time, XPReceived, XPFromTypeID, XPFromRealmID) values (@UserID, GETDATE(), @XPForTitle, 1, @ThisRealmID)
I believe all of these are optimized, yet, it appears we are joining tables over the linked server!
Some interesting wait stats that I do not know how to interpret. Ran a query from http://www.sqlskills.com/blogs/paul/wait-statistics-or-please-tell-me-where-it-hurts/
I get this DURING the CPU spike:
I get this when there is no CPU spike:
These wait times are on the server with DB2, the SQL 2012 server which accesses a remote database on another server running sql server 2008 (for diagram, see https://dba.stackexchange.com/questions/54171/sql-server-2012-performance-issues-maybe-due-to-linked-server
Restarting sql server help - no CPU spike for significant amount of time.
We've also found that, restarting SQL Server helps - we could be getting intermittent spikes for hours, many times an hour, then after restart, no spikes for an hour or more..
Process explorer
As suggested by @EdwardDortland, I used Process explorer to see what thread is consuming most CPU during the slow down
unfortunately, no single thread shows up as the main culprit - during CPU spike, simply all threads consume more CPU. although I am seeing a lot more threads highlighted in red (meaning deleted) during the CPU spike - not sure how to interpret this.
Threads before the CPU spike
Threads during the CPU spike
