Troubleshooting and Optimizing Queries with SQL Azure

- July 27, 2010

In you want to troubleshoot queries performance in SQL Azure, the following paper provides guidelines on the Dynamic Management Views that are available in SQL Azure, and how they can be used for troubleshooting purposes.

http://www.microsoft.com/downloads/details.aspx?FamilyID=0CEB6317-0E52-4A25-8AF2-2702C9C21358&displayLang=en

The following are some examples taken from the paper:

-- Identity excessive recompiles
select top 25 
    sql_text.text, 
    sql_handle, 
    plan_generation_num, 
    execution_count, 
    dbid, 
    objectid  
from  
    sys.dm_exec_query_stats a 
    cross apply sys.dm_exec_sql_text(sql_handle) as sql_text 
where  
    plan_generation_num >1 
order by plan_generation_num desc

-- Inefficient query plans:
select  
    highest_cpu_queries.plan_handle,  
    highest_cpu_queries.total_worker_time, 
    q.dbid, 
    q.objectid, 
    q.number, 
    q.encrypted, 
    q.[text] 
from  
    (select top 50  
        qs.plan_handle,  
        qs.total_worker_time 
    from  
        sys.dm_exec_query_stats qs 
    order by qs.total_worker_time desc) as highest_cpu_queries 
    cross apply sys.dm_exec_sql_text(plan_handle) as q 
order by highest_cpu_queries.total_worker_time desc

-- I/O Bottlenecks
select top 25  
    (total_logical_reads/execution_count) as avg_logical_reads, 
    (total_logical_writes/execution_count) as avg_logical_writes, 
    (total_physical_reads/execution_count) as avg_phys_reads, 
     Execution_count,  
    statement_start_offset as stmt_start_offset,  
    sql_handle,  
    plan_handle 
from sys.dm_exec_query_stats   
order by  
 (total_logical_reads + total_logical_writes) Desc