重新启动或群集故障转移后SQL Server Extreme缓慢

Question

I have a SQL Server 2008 R2 SP1 cluster with 2008 OS. Any time a reboot happens or a failover happens the next several days any processing is extremely slow; however if we leave them running they run much better. I have been researching the possibility when the procedure cache is flushed then with all the plans needing to be rebuilt this is causing the slowness instead of being able to go to memory for the existing plan. Has anyone else experience this and what did you do to resolve so a reboot would not affect the system so negatively?

Answer 1

One thing you can do is monitor your most resource intensive queries after the procedure cache is flushed. Once you ID what queries are taking a long time reading from disk to get put back into the buffer pool, you can schedule a job to spin up those queries immediately after the reboot so when the first user goes to execute it, it is already in the buffer pool and will read from memory instead of disk. Here is a query to find I/O intensive queries after your reboot:

SELECT TOP 25 cp.usecounts AS [execution_count]
      ,qs.total_worker_time AS CPU
      ,qs.total_elapsed_time AS ELAPSED_TIME
      ,qs.total_logical_reads AS LOGICAL_READS
      ,qs.total_logical_writes AS LOGICAL_WRITES
      ,qs.total_physical_reads AS PHYSICAL_READS 
      ,SUBSTRING(text, 
                   CASE WHEN statement_start_offset = 0 
                          OR statement_start_offset IS NULL  
                           THEN 1  
                           ELSE statement_start_offset/2 + 1 END, 
                   CASE WHEN statement_end_offset = 0 
                          OR statement_end_offset = -1  
                          OR statement_end_offset IS NULL  
                           THEN LEN(text)  
                           ELSE statement_end_offset/2 END - 
                     CASE WHEN statement_start_offset = 0 
                            OR statement_start_offset IS NULL 
                             THEN 1  
                             ELSE statement_start_offset/2  END + 1 
                  )  AS [Statement]        
FROM sys.dm_exec_query_stats qs  
   join sys.dm_exec_cached_plans cp on qs.plan_handle = cp.plan_handle 
   CROSS APPLY sys.dm_exec_sql_text(cp.plan_handle) st
ORDER BY qs.total_physical_reads DESC;

Answer 2

Rebuilding plan most probably would not be the problem. I see simmilar behaviour on our system, problem is HDD array. I tested if we could move to SSD it would speed up cold start queries more than 10x.