使用DMV，诊断和调优DB性能。

Posted 2021-03-19 ~沉%淀~

使用DMV，诊断和调优DB性能。

查看等待统计信息，找出SQL Server慢在哪里：

SELECT wait_type ,
SUM(wait_time_ms / 1000) AS [wait_time_s]
FROM sys.dm_os_wait_stats DOWS
WHERE wait_type NOT IN (
        N‘BROKER_EVENTHANDLER‘,             N‘BROKER_RECEIVE_WAITFOR‘,
        N‘BROKER_TASK_STOP‘,                N‘BROKER_TO_FLUSH‘,
        N‘BROKER_TRANSMITTER‘,              N‘CHECKPOINT_QUEUE‘,
        N‘CHKPT‘,                           N‘CLR_AUTO_EVENT‘,
        N‘CLR_MANUAL_EVENT‘,                N‘CLR_SEMAPHORE‘,
        N‘DBMIRROR_DBM_EVENT‘,              N‘DBMIRROR_EVENTS_QUEUE‘,
        N‘DBMIRROR_WORKER_QUEUE‘,           N‘DBMIRRORING_CMD‘,
        N‘DIRTY_PAGE_POLL‘,                 N‘DISPATCHER_QUEUE_SEMAPHORE‘,
        N‘EXECSYNC‘,                        N‘FSAGENT‘,
        N‘FT_IFTS_SCHEDULER_IDLE_WAIT‘,     N‘FT_IFTSHC_MUTEX‘,
        N‘HADR_CLUSAPI_CALL‘,               N‘HADR_FILESTREAM_IOMGR_IOCOMPLETION‘,
        N‘HADR_LOGCAPTURE_WAIT‘,            N‘HADR_NOTIFICATION_DEQUEUE‘,
        N‘HADR_TIMER_TASK‘,                 N‘HADR_WORK_QUEUE‘,
        N‘KSOURCE_WAKEUP‘,                  N‘LAZYWRITER_SLEEP‘,
        N‘LOGMGR_QUEUE‘,                    N‘ONDEMAND_TASK_QUEUE‘,
        N‘PWAIT_ALL_COMPONENTS_INITIALIZED‘,
        N‘QDS_PERSIST_TASK_MAIN_LOOP_SLEEP‘,
        N‘QDS_CLEANUP_STALE_QUERIES_TASK_MAIN_LOOP_SLEEP‘,
        N‘REQUEST_FOR_DEADLOCK_SEARCH‘,     N‘RESOURCE_QUEUE‘,
        N‘SERVER_IDLE_CHECK‘,               N‘SLEEP_BPOOL_FLUSH‘,
        N‘SLEEP_DBSTARTUP‘,                 N‘SLEEP_DCOMSTARTUP‘,
        N‘SLEEP_MASTERDBREADY‘,             N‘SLEEP_MASTERMDREADY‘,
        N‘SLEEP_MASTERUPGRADED‘,            N‘SLEEP_MSDBSTARTUP‘,
        N‘SLEEP_SYSTEMTASK‘,                N‘SLEEP_TASK‘,
        N‘SLEEP_TEMPDBSTARTUP‘,             N‘SNI_HTTP_ACCEPT‘,
        N‘SP_SERVER_DIAGNOSTICS_SLEEP‘,     N‘SQLTRACE_BUFFER_FLUSH‘,
        N‘SQLTRACE_INCREMENTAL_FLUSH_SLEEP‘,
        N‘SQLTRACE_WAIT_ENTRIES‘,           N‘WAIT_FOR_RESULTS‘,
        N‘WAITFOR‘,                         N‘WAITFOR_TASKSHUTDOWN‘,
        N‘WAIT_XTP_HOST_WAIT‘,              N‘WAIT_XTP_OFFLINE_CKPT_NEW_LOG‘,
        N‘WAIT_XTP_CKPT_CLOSE‘,             N‘XE_DISPATCHER_JOIN‘,
        N‘XE_DISPATCHER_WAIT‘,              N‘XE_TIMER_EVENT‘)
GROUP BY wait_type
ORDER BY SUM(wait_time_ms) DESC
 
 
WITH [Waits] AS
    (SELECT
        [wait_type],
        [wait_time_ms] / 1000.0 AS [WaitS],
        ([wait_time_ms] - [signal_wait_time_ms]) / 1000.0 AS [ResourceS],
        [signal_wait_time_ms] / 1000.0 AS [SignalS],
        [waiting_tasks_count] AS [WaitCount],
        100.0 * [wait_time_ms] / SUM ([wait_time_ms]) OVER() AS [Percentage],
        ROW_NUMBER() OVER(ORDER BY [wait_time_ms] DESC) AS [RowNum]
    FROM sys.dm_os_wait_stats
    WHERE [wait_type] NOT IN (
        N‘BROKER_EVENTHANDLER‘,             N‘BROKER_RECEIVE_WAITFOR‘,
        N‘BROKER_TASK_STOP‘,                N‘BROKER_TO_FLUSH‘,
        N‘BROKER_TRANSMITTER‘,              N‘CHECKPOINT_QUEUE‘,
        N‘CHKPT‘,                           N‘CLR_AUTO_EVENT‘,
        N‘CLR_MANUAL_EVENT‘,                N‘CLR_SEMAPHORE‘,
        N‘DBMIRROR_DBM_EVENT‘,              N‘DBMIRROR_EVENTS_QUEUE‘,
        N‘DBMIRROR_WORKER_QUEUE‘,           N‘DBMIRRORING_CMD‘,
        N‘DIRTY_PAGE_POLL‘,                 N‘DISPATCHER_QUEUE_SEMAPHORE‘,
        N‘EXECSYNC‘,                        N‘FSAGENT‘,
        N‘FT_IFTS_SCHEDULER_IDLE_WAIT‘,     N‘FT_IFTSHC_MUTEX‘,
        N‘HADR_CLUSAPI_CALL‘,               N‘HADR_FILESTREAM_IOMGR_IOCOMPLETION‘,
        N‘HADR_LOGCAPTURE_WAIT‘,            N‘HADR_NOTIFICATION_DEQUEUE‘,
        N‘HADR_TIMER_TASK‘,                 N‘HADR_WORK_QUEUE‘,
        N‘KSOURCE_WAKEUP‘,                  N‘LAZYWRITER_SLEEP‘,
        N‘LOGMGR_QUEUE‘,                    N‘ONDEMAND_TASK_QUEUE‘,
        N‘PWAIT_ALL_COMPONENTS_INITIALIZED‘,
        N‘QDS_PERSIST_TASK_MAIN_LOOP_SLEEP‘,
        N‘QDS_CLEANUP_STALE_QUERIES_TASK_MAIN_LOOP_SLEEP‘,
        N‘REQUEST_FOR_DEADLOCK_SEARCH‘,     N‘RESOURCE_QUEUE‘,
        N‘SERVER_IDLE_CHECK‘,               N‘SLEEP_BPOOL_FLUSH‘,
        N‘SLEEP_DBSTARTUP‘,                 N‘SLEEP_DCOMSTARTUP‘,
        N‘SLEEP_MASTERDBREADY‘,             N‘SLEEP_MASTERMDREADY‘,
        N‘SLEEP_MASTERUPGRADED‘,            N‘SLEEP_MSDBSTARTUP‘,
        N‘SLEEP_SYSTEMTASK‘,                N‘SLEEP_TASK‘,
        N‘SLEEP_TEMPDBSTARTUP‘,             N‘SNI_HTTP_ACCEPT‘,
        N‘SP_SERVER_DIAGNOSTICS_SLEEP‘,     N‘SQLTRACE_BUFFER_FLUSH‘,
        N‘SQLTRACE_INCREMENTAL_FLUSH_SLEEP‘,
        N‘SQLTRACE_WAIT_ENTRIES‘,           N‘WAIT_FOR_RESULTS‘,
        N‘WAITFOR‘,                         N‘WAITFOR_TASKSHUTDOWN‘,
        N‘WAIT_XTP_HOST_WAIT‘,              N‘WAIT_XTP_OFFLINE_CKPT_NEW_LOG‘,
        N‘WAIT_XTP_CKPT_CLOSE‘,             N‘XE_DISPATCHER_JOIN‘,
        N‘XE_DISPATCHER_WAIT‘,              N‘XE_TIMER_EVENT‘)
    AND [waiting_tasks_count] > 0
 )
SELECT
    MAX ([W1].[wait_type]) AS [WaitType],
    CAST (MAX ([W1].[WaitS]) AS DECIMAL (16,2)) AS [Wait_S],
    CAST (MAX ([W1].[ResourceS]) AS DECIMAL (16,2)) AS [Resource_S],
    CAST (MAX ([W1].[SignalS]) AS DECIMAL (16,2)) AS [Signal_S],
    MAX ([W1].[WaitCount]) AS [WaitCount],
    CAST (MAX ([W1].[Percentage]) AS DECIMAL (5,2)) AS [Percentage],
    CAST ((MAX ([W1].[WaitS]) / MAX ([W1].[WaitCount])) AS DECIMAL (16,4)) AS [AvgWait_S],
    CAST ((MAX ([W1].[ResourceS]) / MAX ([W1].[WaitCount])) AS DECIMAL (16,4)) AS [AvgRes_S],
    CAST ((MAX ([W1].[SignalS]) / MAX ([W1].[WaitCount])) AS DECIMAL (16,4)) AS [AvgSig_S]
FROM [Waits] AS [W1]
INNER JOIN [Waits] AS [W2]
    ON [W2].[RowNum] <= [W1].[RowNum]
GROUP BY [W1].[RowNum]
HAVING SUM ([W2].[Percentage]) - MAX ([W1].[Percentage]) < 95; -- percentage threshold
GO
获取一段时间内累计的File reads：



SELECT DB_NAME(mf.database_id) AS databaseName ,
mf.physical_name ,
divfs.num_of_reads ,
--other columns removed in this section. See Listing 6.14 for complete code
GETDATE() AS baselineDate
INTO #baseline
FROM sys.dm_io_virtual_file_stats(NULL, NULL) AS divfs
JOIN sys.master_files AS mf ON mf.database_id = divfs.database_id
AND mf.file_id = divfs.file_id
 
--过一段时间后执行下面的SQL
 
WITH currentLine
AS ( SELECT DB_NAME(mf.database_id) AS databaseName ,
mf.physical_name ,
num_of_reads ,
--other columms removed
GETDATE() AS currentlineDate
FROM sys.dm_io_virtual_file_stats(NULL, NULL) AS divfs
JOIN sys.master_files AS mf
ON mf.database_id = divfs.database_id
AND mf.file_id = divfs.file_id
)
SELECT currentLine.databaseName ,
currentLine.physical_name ,
--gets the time difference in milliseconds since the baseline was taken
DATEDIFF(millisecond,baseLineDate,currentLineDate) AS elapsed_ms,
--gets the change in time since the baseline was taken
currentLine.num_of_reads - #baseline.num_of_reads AS num_of_reads
--other columns removed
FROM currentLine
INNER JOIN #baseline ON #baseLine.databaseName = currentLine.databaseName
AND #baseLine.physical_name = currentLine.physical_name
根据IP获取连接个数

-- Get a count of SQL connections by IP address
SELECT dec.client_net_address ,
des.program_name ,
des.host_name ,
--des.login_name ,
COUNT(dec.session_id) AS connection_count
FROM sys.dm_exec_sessions AS des
INNER JOIN sys.dm_exec_connections AS dec
ON des.session_id = dec.session_id
-- WHERE LEFT(des.host_name, 2) = ‘WK‘
GROUP BY dec.client_net_address ,
des.program_name ,
des.host_name
-- des.login_name
-- HAVING COUNT(dec.session_id) > 1
ORDER BY des.program_name,
dec.client_net_address ;
查看谁在通过SSMS执行什么

SELECT dec.client_net_address ,
des.host_name ,
dest.text
FROM sys.dm_exec_sessions des
INNER JOIN sys.dm_exec_connections dec
ON des.session_id = dec.session_id
CROSS APPLY sys.dm_exec_sql_text(dec.most_recent_sql_handle) dest
WHERE des.program_name LIKE ‘Microsoft SQL Server Management Studio%‘
ORDER BY des.program_name ,
dec.client_net_address
查看当前session的session级别的设置
SELECT des.text_size ,
des.language ,
des.date_format ,
des.date_first ,
des.quoted_identifier ,
des.arithabort ,
des.ansi_null_dflt_on ,
des.ansi_defaults ,
des.ansi_warnings ,
des.ansi_padding ,
des.ansi_nulls ,
des.concat_null_yields_null ,
des.transaction_isolation_level ,
des.lock_timeout ,
des.deadlock_priority
FROM sys.dm_exec_sessions des
WHERE des.session_id = @@SPID
查看超过一个session的登录信息

SELECT login_name ,
COUNT(session_id) AS session_count
FROM sys.dm_exec_sessions
WHERE is_user_process = 1
GROUP BY login_name
ORDER BY login_name
识别有context swithing的sessions信息

SELECT session_id ,
login_name ,
original_login_name
FROM sys.dm_exec_sessions
WHERE is_user_process = 1
AND login_name <> original_login_name
识别不活动的sessions

DECLARE @days_old SMALLINT
SELECT @days_old = 5
SELECT des.session_id ,
des.login_time ,
des.last_request_start_time ,
des.last_request_end_time ,
des.[status] ,
des.[program_name] ,
des.cpu_time ,
des.total_elapsed_time ,
des.memory_usage ,
des.total_scheduled_time ,
des.total_elapsed_time ,
des.reads ,
des.writes ,
des.logical_reads ,
des.row_count ,
des.is_user_process
FROM sys.dm_exec_sessions des
INNER JOIN sys.dm_tran_session_transactions dtst
ON des.session_id = dtst.session_id
WHERE des.is_user_process = 1
AND DATEDIFF(dd, des.last_request_end_time, GETDATE()) > @days_old
AND des.status != ‘Running‘
ORDER BY des.last_request_end_time
识别孤立事务引起的闲置sessions

SELECT des.session_id ,
des.login_time ,
des.last_request_start_time ,
des.last_request_end_time ,
des.host_name ,
des.login_name
FROM sys.dm_exec_sessions des
INNER JOIN sys.dm_tran_session_transactions dtst
ON des.session_id = dtst.session_id
LEFT JOIN sys.dm_exec_requests der
ON dtst.session_id = der.session_id
WHERE der.session_id IS NULL
ORDER BY des.session_id
查看当前活动请求的执行计划、CPU消耗等

SELECT der.session_id ,
DB_NAME(der.database_id) AS database_name ,
deqp.query_plan ,
SUBSTRING(dest.text, der.statement_start_offset / 2,
( CASE WHEN der.statement_end_offset = -1
THEN DATALENGTH(dest.text)
ELSE der.statement_end_offset
END - der.statement_start_offset ) / 2)
AS [statement executing] ,
der.cpu_time
--der.granted_query_memory
--der.wait_time
--der.total_elapsed_time
--der.reads
FROM sys.dm_exec_requests der
INNER JOIN sys.dm_exec_sessions des
ON des.session_id = der.session_id
CROSS APPLY sys.dm_exec_sql_text(der.sql_handle) dest
CROSS APPLY sys.dm_exec_query_plan(der.plan_handle) deqp
WHERE des.is_user_process = 1
AND der.session_id <> @@spid
ORDER BY der.cpu_time DESC ;
-- ORDER BY der.granted_query_memory DESC ;
-- ORDER BY der.wait_time DESC;
-- ORDER BY der.total_elapsed_time DESC;
-- ORDER BY der.reads DESC;
查看当前谁在运行什么

-- Who is running what at this instant
SELECT dest.text AS [Command text] ,
des.login_time ,
des.[host_name] ,
des.[program_name] ,
der.session_id ,
dec.client_net_address ,
der.status ,
der.command ,
DB_NAME(der.database_id) AS DatabaseName
FROM sys.dm_exec_requests der
INNER JOIN sys.dm_exec_connections dec
ON der.session_id = dec.session_id
INNER JOIN sys.dm_exec_sessions des
ON des.session_id = der.session_id
CROSS APPLY sys.dm_exec_sql_text(sql_handle) AS dest
WHERE des.is_user_process = 1
比SP_WHO2更好的SQL

SELECT des.session_id ,
des.status ,
des.login_name ,
des.[HOST_NAME] ,
der.blocking_session_id ,
DB_NAME(der.database_id) AS database_name ,
der.command ,
des.cpu_time ,
des.reads ,
des.writes ,
dec.last_write ,
des.[program_name] ,
der.wait_type ,
der.wait_time ,
der.last_wait_type ,
der.wait_resource ,
CASE des.transaction_isolation_level
WHEN 0 THEN ‘Unspecified‘
WHEN 1 THEN ‘ReadUncommitted‘
WHEN 2 THEN ‘ReadCommitted‘
WHEN 3 THEN ‘Repeatable‘
WHEN 4 THEN ‘Serializable‘
WHEN 5 THEN ‘Snapshot‘
END AS transaction_isolation_level ,
OBJECT_NAME(dest.objectid, der.database_id) AS OBJECT_NAME ,
SUBSTRING(dest.text, der.statement_start_offset / 2,
( CASE WHEN der.statement_end_offset = -1
THEN DATALENGTH(dest.text)
ELSE der.statement_end_offset
END - der.statement_start_offset ) / 2)
AS [executing statement] ,
deqp.query_plan
FROM sys.dm_exec_sessions des
LEFT JOIN sys.dm_exec_requests der
ON des.session_id = der.session_id
LEFT JOIN sys.dm_exec_connections dec
ON des.session_id = dec.session_id
CROSS APPLY sys.dm_exec_sql_text(der.sql_handle) dest
CROSS APPLY sys.dm_exec_query_plan(der.plan_handle) deqp
WHERE des.session_id <> @@SPID
ORDER BY des.session_id
清除指定数据库的计划缓存

--Determine the id of your database
DECLARE @intDBID INTEGER
SET @intDBID = ( SELECT dbid
FROM master.dbo.sysdatabases
WHERE name = ‘mydatabasename‘
)
--Flush the procedure cache for your database
DBCC FLUSHPROCINDB (@intDBID)
Retrieving the text for a currently executing ad hoc query

SELECT dest.text ,
dest.dbid ,
dest.objectid
FROM sys.dm_exec_requests AS der
CROSS APPLY sys.dm_exec_sql_text(der.sql_handle) AS dest
WHERE session_id = @@spid ;
Retrieving the text for a currently executing batch
SELECT dest.text
FROM sys.dm_exec_requests AS der
CROSS APPLY sys.dm_exec_sql_text(der.sql_handle) AS dest
WHERE session_id <> @@spid
AND text LIKE ‘%waitfor%‘ ;
Returning the text of an executing stored procedure
SELECT dest.dbid ,
dest.objectid ,
dest.encrypted ,
dest.text
FROM sys.dm_exec_requests AS der
CROSS APPLY sys.dm_exec_sql_text(der.sql_handle)
AS dest
WHERE objectid = object_id(‘test‘, ‘p‘);

Parsing the SQL text using statement_start_offset and statement_end_offset
SELECT der.statement_start_offset ,
der.statement_end_offset ,
SUBSTRING(dest.text, der.statement_start_offset / 2,
( CASE WHEN der.statement_end_offset = -1
THEN DATALENGTH(dest.text)
ELSE der.statement_end_offset
END - der.statement_start_offset ) / 2)
AS statement_executing ,
dest.text AS [full statement code]
FROM sys.dm_exec_requests der
INNER JOIN sys.dm_exec_sessions des
ON des.session_id = der.session_id
CROSS APPLY sys.dm_exec_sql_text(der.sql_handle) dest
WHERE des.is_user_process = 1
AND der.session_id <> @@spid
ORDER BY der.session_id ;

Investigating offsets.
WAITFOR DELAY ‘00:01‘ ;
BEGIN TRANSACTION
-- WAITFOR DELAY ‘00:01‘ ;
INSERT INTO AdventureWorks.Production.ProductCategory
( Name, ModifiedDate )
VALUES ( ‘Reflectors‘, GETDATE() )
ROLLBACK TRANSACTION
SELECT Name ,
ModifiedDate
FROM AdventureWorks.Production.ProductCategory
WHERE Name = ‘Reflectors‘ ;
-- WAITFOR DELAY ‘00:01‘ ;

Requests by CPU consumption
SELECT der.session_id ,
DB_NAME(der.database_id) AS database_name ,
deqp.query_plan ,
SUBSTRING(dest.text, der.statement_start_offset / 2,
( CASE WHEN der.statement_end_offset = -1
THEN DATALENGTH(dest.text)
ELSE der.statement_end_offset
END - der.statement_start_offset ) / 2)
AS [statement executing] ,
der.cpu_time
--der.granted_query_memory
--der.wait_time
--der.total_elapsed_time
--der.reads
FROM sys.dm_exec_requests der
INNER JOIN sys.dm_exec_sessions des
ON des.session_id = der.session_id
CROSS APPLY sys.dm_exec_sql_text(der.sql_handle) dest
CROSS APPLY sys.dm_exec_query_plan(der.plan_handle) deqp
WHERE des.is_user_process = 1
AND der.session_id <> @@spid
ORDER BY der.cpu_time DESC ;
-- ORDER BY der.granted_query_memory DESC ;
-- ORDER BY der.wait_time DESC;
-- ORDER BY der.total_elapsed_time DESC;
-- ORDER BY der.reads DESC;
Who is running what

-- Who is running what at this instant
SELECT dest.text AS [Command text] ,
des.login_time ,
des.[host_name] ,
des.[program_name] ,
der.session_id ,
dec.client_net_address ,
der.status ,
der.command ,
DB_NAME(der.database_id) AS DatabaseName
FROM sys.dm_exec_requests der
INNER JOIN sys.dm_exec_connections dec
ON der.session_id = dec.session_id
INNER JOIN sys.dm_exec_sessions des
ON des.session_id = der.session_id
CROSS APPLY sys.dm_exec_sql_text(sql_handle) AS dest
WHERE des.is_user_process = 1

Flushing the cache of plans belonging to a particular database.

--Determine the id of your database
DECLARE @intDBID INTEGER
SET @intDBID = ( SELECT dbid
FROM master.dbo.sysdatabases
WHERE name = ‘mydatabasename‘
)
--Flush the procedure cache for your database
DBCC FLUSHPROCINDB (@intDBID)

Retrieving the query plan for a cached stored procedure
CREATE PROCEDURE ShowQueryText
AS
SELECT TOP 10
object_id ,
name
FROM sys.objects ;
--waitfor delay ‘00:00:00‘
 
SELECT TOP 10
object_id ,
name
FROM sys.objects ;
SELECT TOP 10
object_id ,
name
FROM sys.procedures ;
GO
EXEC dbo.ShowQueryText ;
GO
SELECT deqp.dbid ,
deqp.objectid ,
deqp.encrypted ,
deqp.query_plan
FROM sys.dm_exec_query_stats deqs
CROSS APPLY sys.dm_exec_query_plan(deqs.plan_handle) AS deqp
WHERE objectid = OBJECT_ID(‘ShowQueryText‘, ‘p‘) ;

Viewing the sql_handle and plan_handle.
SELECT deqs.plan_handle ,
deqs.sql_handle ,
execText.text
FROM sys.dm_exec_query_stats deqs
CROSS APPLY sys.dm_exec_sql_text(deqs.plan_handle) AS execText
WHERE execText.text LIKE ‘CREATE PROCEDURE ShowQueryText%‘

Extracting the SQL text for individual queries in a batch.
SELECT CHAR(13) + CHAR(10)
+ CASE WHEN deqs.statement_start_offset = 0
AND deqs.statement_end_offset = -1
THEN ‘-- see objectText column--‘
ELSE ‘-- query --‘ + CHAR(13) + CHAR(10)
+ SUBSTRING(execText.text, deqs.statement_start_offset / 2,
( ( CASE WHEN deqs.statement_end_offset = -1
THEN DATALENGTH(execText.text)
ELSE deqs.statement_end_offset
END ) - deqs.statement_start_offset ) / 2)
END AS queryText ,
deqp.query_plan
FROM sys.dm_exec_query_stats deqs
CROSS APPLY sys.dm_exec_sql_text(deqs.plan_handle) AS execText
CROSS APPLY sys.dm_exec_query_plan(deqs.plan_handle) deqp
WHERE execText.text LIKE ‘CREATE PROCEDURE ShowQueryText%‘

Returning the plan using sys.dm_exec_text_query_plan.
SELECT deqp.dbid ,
deqp.objectid ,
CAST(detqp.query_plan AS XML) AS singleStatementPlan ,
deqp.query_plan AS batch_query_plan ,
--this won‘t actually work in all cases because nominal plans aren‘t
-- cached, so you won‘t see a plan for waitfor if you uncomment it
ROW_NUMBER() OVER ( ORDER BY Statement_Start_offset )
AS query_position ,
CASE WHEN deqs.statement_start_offset = 0
AND deqs.statement_end_offset = -1
THEN ‘-- see objectText column--‘
ELSE ‘-- query --‘ + CHAR(13) + CHAR(10)
+ SUBSTRING(execText.text, deqs.statement_start_offset / 2,
( ( CASE WHEN deqs.statement_end_offset = -1
THEN DATALENGTH(execText.text)
ELSE deqs.statement_end_offset
END ) - deqs.statement_start_offset ) / 2)
END AS queryText
FROM sys.dm_exec_query_stats deqs
CROSS APPLY sys.dm_exec_text_query_plan(deqs.plan_handle,
deqs.statement_start_offset,
deqs.statement_end_offset)
AS detqp
CROSS APPLY sys.dm_exec_query_plan(deqs.plan_handle) AS deqp
CROSS APPLY sys.dm_exec_sql_text(deqs.plan_handle) AS execText
WHERE deqp.objectid = OBJECT_ID(‘ShowQueryText‘, ‘p‘) ;

Retrieving the plans for compiled objects.
SELECT refcounts ,
usecounts ,
size_in_bytes ,
cacheobjtype ,
objtype
FROM sys.dm_exec_cached_plans
WHERE objtype IN ( ‘proc‘, ‘prepared‘ ) ;

Total number of cached plans.
SELECT COUNT(*)
FROM sys.dm_exec_cached_plans ;

An overview of plan reuse.
SELECT MAX(CASE WHEN usecounts BETWEEN 10 AND 100 THEN ‘10-100‘
WHEN usecounts BETWEEN 101 AND 1000 THEN ‘101-1000‘
WHEN usecounts BETWEEN 1001 AND 5000 THEN ‘1001-5000‘
WHEN usecounts BETWEEN 5001 AND 10000 THEN ‘5001-10000‘
ELSE CAST(usecounts AS VARCHAR(100))
END) AS usecounts ,
COUNT(*) AS countInstance
FROM sys.dm_exec_cached_plans
GROUP BY CASE WHEN usecounts BETWEEN 10 AND 100 THEN 50
WHEN usecounts BETWEEN 101 AND 1000 THEN 500
WHEN usecounts BETWEEN 1001 AND 5000 THEN 2500
WHEN usecounts BETWEEN 5001 AND 10000 THEN 7500
ELSE usecounts
END
ORDER BY CASE WHEN usecounts BETWEEN 10 AND 100 THEN 50
WHEN usecounts BETWEEN 101 AND 1000 THEN 500
WHEN usecounts BETWEEN 1001 AND 5000 THEN 2500
WHEN usecounts BETWEEN 5001 AND 10000 THEN 7500
ELSE usecounts
END DESC ;

Investigating the most used plans.
SELECT TOP 2 WITH TIES
decp.usecounts ,
decp.cacheobjtype ,
decp.objtype ,
deqp.query_plan ,
dest.text
FROM sys.dm_exec_cached_plans decp
CROSS APPLY sys.dm_exec_query_plan(decp.plan_handle) AS deqp
CROSS APPLY sys.dm_exec_sql_text(decp.plan_handle) AS dest
ORDER BY usecounts DESC ;

Examining plan reuse for a single procedure
 SELECT usecounts ,
cacheobjtype ,
objtype ,
OBJECT_NAME(dest.objectid)
FROM sys.dm_exec_cached_plans decp
CROSS APPLY sys.dm_exec_sql_text(decp.plan_handle) AS dest
WHERE dest.objectid = OBJECT_ID(‘<procedureName>‘)
AND dest.dbid = DB_ID()
ORDER BY usecounts DESC ;

Examining single-use plans in the cache
-- Find single-use, ad hoc queries that are bloating the plan cache
SELECT TOP ( 100 )
[text] ,
cp.size_in_bytes
FROM sys.dm_exec_cached_plans AS cp
CROSS APPLY sys.dm_exec_sql_text(plan_handle)
WHERE cp.cacheobjtype = ‘Compiled Plan‘
AND cp.objtype = ‘Adhoc‘
AND cp.usecounts = 1
ORDER BY cp.size_in_bytes DESC ;

Examining plan attributes.
SELECT CAST(depa.attribute AS VARCHAR(30)) AS attribute ,
CAST(depa.value AS VARCHAR(30)) AS value ,
depa.is_cache_key
FROM ( SELECT TOP 1
*
FROM sys.dm_exec_cached_plans
ORDER BY usecounts DESC
) decp
OUTER APPLY sys.dm_exec_plan_attributes(decp.plan_handle) depa
WHERE is_cache_key = 1
ORDER BY usecounts DESC ;

Finding the CPU-intensive queries.
 SELECT TOP 3
total_worker_time ,
execution_count ,
total_worker_time / execution_count AS [Avg CPU Time] ,
CASE WHEN deqs.statement_start_offset = 0
AND deqs.statement_end_offset = -1
THEN ‘-- see objectText column--‘
ELSE ‘-- query --‘ + CHAR(13) + CHAR(10)
+ SUBSTRING(execText.text, deqs.statement_start_offset / 2,
( ( CASE WHEN deqs.statement_end_offset = -1
THEN DATALENGTH(execText.text)
ELSE deqs.statement_end_offset
END ) - deqs.statement_start_offset ) / 2)
END AS queryText
FROM sys.dm_exec_query_stats deqs
CROSS APPLY sys.dm_exec_sql_text(deqs.plan_handle) AS execText
ORDER BY deqs.total_worker_time DESC ;

Grouping by sql_handle to see query stats at the batch level.
SELECT TOP 100
SUM(total_logical_reads) AS total_logical_reads ,
COUNT(*) AS num_queries , --number of individual queries in batch
--not all usages need be equivalent, in the case of looping
--or branching code
MAX(execution_count) AS execution_count ,
MAX(execText.text) AS queryText
FROM sys.dm_exec_query_stats deqs
CROSS APPLY sys.dm_exec_sql_text(deqs.sql_handle) AS execText
GROUP BY deqs.sql_handle
HAVING AVG(total_logical_reads / execution_count) <> SUM(total_logical_reads)
/ SUM(execution_count)
ORDER BY 1 DESC

Investigating logical reads performed by cached stored procedures.
-- Top Cached SPs By Total Logical Reads (SQL 2008 only).
-- Logical reads relate to memory pressure
SELECT TOP ( 25 )
p.name AS [SP Name] ,
deps.total_logical_reads AS [TotalLogicalReads] ,
deps.total_logical_reads / deps.execution_count AS [AvgLogicalReads] ,
deps.execution_count ,
ISNULL(deps.execution_count / DATEDIFF(Second, deps.cached_time,
GETDATE()), 0) AS [Calls/Second] ,
deps.total_elapsed_time ,
deps.total_elapsed_time / deps.execution_count AS [avg_elapsed_time] ,
deps.cached_time
FROM sys.procedures AS p
INNER JOIN sys.dm_exec_procedure_stats
AS deps ON p.[object_id] = deps.[object_id]
WHERE deps.database_id = DB_ID()
ORDER BY deps.total_logical_reads DESC ;

Examine optimizer counters.
SELECT counter ,
occurrence ,
value
FROM sys.dm_exec_query_optimizer_info
WHERE counter IN ( ‘optimizations‘, ‘elapsed time‘, ‘final cost‘ ) ;
Trivial changes to query text can affect plan reuse.
SELECT COUNTER ,
OCCURRENCE ,
VALUE
FROM SYS.DM_EXEC_QUERY_OPTIMIZER_INFO
WHERE COUNTER IN ( ‘optimizations‘, ‘elapsed time‘, ‘final cost‘ ) ;

Locking due to single UPDATE statement against a user table in SQL Server
SELECT [resource_type] ,
DB_NAME([resource_database_id]) AS [Database Name] ,
CASE WHEN DTL.resource_type IN ( ‘DATABASE‘, ‘FILE‘, ‘METADATA‘ )
THEN DTL.resource_type
WHEN DTL.resource_type = ‘OBJECT‘
THEN OBJECT_NAME(DTL.resource_associated_entity_id,
DTL.[resource_database_id])
WHEN DTL.resource_type IN ( ‘KEY‘, ‘PAGE‘, ‘RID‘ )
THEN ( SELECT OBJECT_NAME([object_id])
FROM sys.partitions
WHERE sys.partitions.hobt_id =
DTL.resource_associated_entity_id
)
ELSE ‘Unidentified‘
END AS requested_object_name ,
[request_mode] ,
[resource_description]
FROM sys.dm_tran_locks DTL
WHERE DTL.[resource_type] <> ‘DATABASE‘ ;

Which sessions are causing blocking and what statement are they running?
SELECT DTL.[request_session_id] AS [session_id] ,
DB_NAME(DTL.[resource_database_id]) AS [Database] ,
DTL.resource_type ,
CASE WHEN DTL.resource_type IN ( ‘DATABASE‘, ‘FILE‘, ‘METADATA‘ )
THEN DTL.resource_type
WHEN DTL.resource_type = ‘OBJECT‘
THEN OBJECT_NAME(DTL.resource_associated_entity_id,
DTL.[resource_database_id])
WHEN DTL.resource_type IN ( ‘KEY‘, ‘PAGE‘, ‘RID‘ )
THEN ( SELECT OBJECT_NAME([object_id])
FROM sys.partitions
WHERE sys.partitions.hobt_id =
DTL.resource_associated_entity_id
)
ELSE ‘Unidentified‘
END AS [Parent Object] ,
DTL.request_mode AS [Lock Type] ,
DTL.request_status AS [Request Status] ,
DER.[blocking_session_id] ,
DES.[login_name] ,
CASE DTL.request_lifetime
WHEN 0 THEN DEST_R.TEXT
ELSE DEST_C.TEXT
END AS [Statement]
FROM sys.dm_tran_locks DTL
LEFT JOIN sys.[dm_exec_requests] DER
ON DTL.[request_session_id] = DER.[session_id]
INNER JOIN sys.dm_exec_sessions DES
ON DTL.request_session_id = DES.[session_id]
INNER JOIN sys.dm_exec_connections DEC
ON DTL.[request_session_id] = DEC.[most_recent_session_id]
OUTER APPLY sys.dm_exec_sql_text(DEC.[most_recent_sql_handle])
AS DEST_C
OUTER APPLY sys.dm_exec_sql_text(DER.sql_handle) AS DEST_R
WHERE DTL.[resource_database_id] = DB_ID()
AND DTL.[resource_type] NOT IN ( ‘DATABASE‘, ‘METADATA‘ )
ORDER BY DTL.[request_session_id] ;

Investigating locking and blocking based on waiting tasks.
SELECT DTL.[resource_type] AS [resource type] ,
CASE WHEN DTL.[resource_type] IN ( ‘DATABASE‘, ‘FILE‘, ‘METADATA‘ )
THEN DTL.[resource_type]
WHEN DTL.[resource_type] = ‘OBJECT‘
THEN OBJECT_NAME(DTL.resource_associated_entity_id)
WHEN DTL.[resource_type] IN ( ‘KEY‘, ‘PAGE‘, ‘RID‘ )
THEN ( SELECT OBJECT_NAME([object_id])
FROM sys.partitions
WHERE sys.partitions.[hobt_id] =
DTL.[resource_associated_entity_id]
)
ELSE ‘Unidentified‘
END AS [Parent Object] ,
DTL.[request_mode] AS [Lock Type] ,
DTL.[request_status] AS [Request Status] ,
DOWT.[wait_duration_ms] AS [wait duration ms] ,
DOWT.[wait_type] AS [wait type] ,
DOWT.[session_id] AS [blocked session id] ,
DES_blocked.[login_name] AS [blocked_user] ,
SUBSTRING(dest_blocked.text, der.statement_start_offset / 2,
( CASE WHEN der.statement_end_offset = -1
THEN DATALENGTH(dest_blocked.text)
ELSE der.statement_end_offset
END - der.statement_start_offset ) / 2
AS [blocked_command] ,
DOWT.[blocking_session_id] AS [blocking session id] ,
DES_blocking.[login_name] AS [blocking user] ,
DEST_blocking.[text] AS [blocking command] ,
DOWT.resource_description AS [blocking resource detail]
FROM sys.dm_tran_locks DTL
INNER JOIN sys.dm_os_waiting_tasks DOWT
ON DTL.lock_owner_address = DOWT.resource_address
INNER JOIN sys.[dm_exec_requests] DER
ON DOWT.[session_id] = DER.[session_id]
INNER JOIN sys.dm_exec_sessions DES_blocked
ON DOWT.[session_id] = DES_Blocked.[session_id]
INNER JOIN sys.dm_exec_sessions DES_blocking
ON DOWT.[blocking_session_id] = DES_Blocking.[session_id]
INNER JOIN sys.dm_exec_connections DEC
ON DTL.[request_session_id] = DEC.[most_recent_session_id]
CROSS APPLY sys.dm_exec_sql_text(DEC.[most_recent_sql_handle])
AS DEST_Blocking
CROSS APPLY sys.dm_exec_sql_text(DER.sql_handle) AS DEST_Blocked
WHERE DTL.[resource_database_id] = DB_ID()

Querying sys.dm_db_tran_active_transactions
 SELECT DTAT.transaction_id ,
DTAT.[name] ,
DTAT.transaction_begin_time ,
CASE DTAT.transaction_type
WHEN 1 THEN ‘Read/write‘
WHEN 2 THEN ‘Read-only‘
WHEN 3 THEN ‘System‘
WHEN 4 THEN ‘Distributed‘
END AS transaction_type ,
CASE DTAT.transaction_state
WHEN 0 THEN ‘Not fully initialized‘
WHEN 1 THEN ‘Initialized, not started‘
WHEN 2 THEN ‘Active‘
WHEN 3 THEN ‘Ended‘ -- only applies to read-only transactions
WHEN 4 THEN ‘Commit initiated‘-- distributed transactions only
WHEN 5 THEN ‘Prepared, awaiting resolution‘
WHEN 6 THEN ‘Committed‘
WHEN 7 THEN ‘Rolling back‘
WHEN 8 THEN ‘Rolled back‘
END AS transaction_state ,
CASE DTAT.dtc_state
WHEN 1 THEN ‘Active‘
WHEN 2 THEN ‘Prepared‘
WHEN 3 THEN ‘Committed‘
WHEN 4 THEN ‘Aborted‘
WHEN 5 THEN ‘Recovered‘
END AS dtc_state
FROM sys.dm_tran_active_transactions DTAT
INNER JOIN sys.dm_tran_session_transactions DTST
ON DTAT.transaction_id = DTST.transaction_id
WHERE [DTST].[is_user_transaction] = 1
ORDER BY DTAT.transaction_begin_time
Eliminating worktables from the results returned by active_transactions.
FROM sys.dm_tran_active_transactions DTAT
WHERE DTAT.name <> ‘worktable‘
ORDER BY DTAT.transaction_begin_time
Decoding the integer values returned by database_transaction_state.

CASE SDTDT.database_transaction_state
WHEN 1 THEN ‘Not initialized‘
WHEN 3 THEN ‘initialized, but not producing log records‘
WHEN 4 THEN ‘Producing log records‘
WHEN 5 THEN ‘Prepared‘
WHEN 10 THEN ‘Committed‘
WHEN 11 THEN ‘Rolled back‘
WHEN 12 THEN ‘Commit in process‘

Transaction log impact of active transactions.

SELECT DTST.[session_id],
DES.[login_name] AS [Login Name],
DB_NAME (DTDT.database_id) AS [Database],
DTDT.[database_transaction_begin_time] AS [Begin Time],
-- DATEDIFF(ms,DTDT.[database_transaction_begin_time], GETDATE()) AS [Duration
ms],
CASE DTAT.transaction_type
WHEN 1 THEN ‘Read/write‘
WHEN 2 THEN ‘Read-only‘
WHEN 3 THEN ‘System‘
WHEN 4 THEN ‘Distributed‘
END AS [Transaction Type],
CASE DTAT.transaction_state
WHEN 0 THEN ‘Not fully initialized‘
WHEN 1 THEN ‘Initialized, not started‘
WHEN 2 THEN ‘Active‘
WHEN 3 THEN ‘Ended‘
WHEN 4 THEN ‘Commit initiated‘
WHEN 5 THEN ‘Prepared, awaiting resolution‘
WHEN 6 THEN ‘Committed‘
WHEN 7 THEN ‘Rolling back‘
WHEN 8 THEN ‘Rolled back‘
END AS [Transaction State],
DTDT.[database_transaction_log_record_count] AS [Log Records],
DTDT.[database_transaction_log_bytes_used] AS [Log Bytes Used],
DTDT.[database_transaction_log_bytes_reserved] AS [Log Bytes RSVPd],
DEST.[text] AS [Last Transaction Text],
DEQP.[query_plan] AS [Last Query Plan]
FROM sys.dm_tran_database_transactions DTDT
INNER JOIN sys.dm_tran_session_transactions DTST
ON DTST.[transaction_id] = DTDT.[transaction_id]
INNER JOIN sys.[dm_tran_active_transactions] DTAT
ON DTST.[transaction_id] = DTAT.[transaction_id]
INNER JOIN sys.[dm_exec_sessions] DES
ON DES.[session_id] = DTST.[session_id]
INNER JOIN sys.dm_exec_connections DEC
ON DEC.[session_id] = DTST.[session_id]
LEFT JOIN sys.dm_exec_requests DER
ON DER.[session_id] = DTST.[session_id]
CROSS APPLY sys.dm_exec_sql_text (DEC.[most_recent_sql_handle]) AS DEST
OUTER APPLY sys.dm_exec_query_plan (DER.[plan_handle]) AS DEQP
ORDER BY DTDT.[database_transaction_log_bytes_used] DESC;
-- ORDER BY [Duration ms] DESC;

Which databases are using snapshot isolation
SELECT SD.[name] ,
SD.snapshot_isolation_state_desc ,
SD.is_read_committed_snapshot_on
FROM sys.databases SD
WHERE SD.snapshot_isolation_state_desc = ‘ON‘

Interrogating the active_snapshot_database_transactions DMV
 SELECT DTASDT.transaction_id ,
DTASDT.session_id ,
DTASDT.transaction_sequence_num ,
DTASDT.first_snapshot_sequence_num ,
DTASDT.commit_sequence_num ,
DTASDT.is_snapshot ,
DTASDT.elapsed_time_seconds ,
DEST.text AS [command text]
FROM sys.dm_tran_active_snapshot_database_transactions DTASDT
INNER JOIN sys.dm_exec_connections DEC
ON DTASDT.session_id = DEC.most_recent_session_id
INNER JOIN sys.dm_tran_database_transactions DTDT
ON DTASDT.transaction_id = DTDT.transaction_id
CROSS APPLY sys.dm_exec_sql_text(DEC.most_recent_sql_handle) AS DEST
WHERE DTDT.database_id = DB_ID()

Correlating the activity of the various transactions that are using the version store
SELECT DTTS.[transaction_sequence_num] ,
trx_current.[session_id] AS current_session_id ,
DES_current.[login_name] AS [current session login] ,
DEST_current.text AS [current session command] ,
DTTS.[snapshot_sequence_num] ,
trx_existing.[session_id] AS existing_session_id ,
DES_existing.[login_name] AS [existing session login] ,
DEST_existing.text AS [existing session command]
FROM sys.dm_tran_transactions_snapshot DTTS
INNER JOIN sys.[dm_tran_active_snapshot_database_transactions]
trx_current
ON DTTS.[transaction_sequence_num] =
trx_current.[transaction_sequence_num]
INNER JOIN sys.[dm_exec_connections] DEC_current
ON trx_current.[session_id] =
DEC_current.[most_recent_session_id]
INNER JOIN sys.[dm_exec_sessions] DES_current
ON DEC_current.[most_recent_session_id] =
DES_current.[session_id]
INNER JOIN sys.[dm_tran_active_snapshot_database_transactions]
trx_existing
ON DTTS.[snapshot_sequence_num] =
trx_existing.[transaction_sequence_num]
INNER JOIN sys.[dm_exec_connections] DEC_existing
ON trx_existing.[session_id] =
DEC_existing.[most_recent_session_id]
INNER JOIN sys.[dm_exec_sessions] DES_existing
ON DEC_existing.[most_recent_session_id] =
DES_existing.[session_id]
CROSS APPLY sys.[dm_exec_sql_text]
(DEC_current.[most_recent_sql_handle]) DEST_current
CROSS APPLY sys.[dm_exec_sql_text]
(DEC_existing.[most_recent_sql_handle]) DEST_existing
ORDER BY DTTS.[transaction_sequence_num] ,
DTTS.[snapshot_sequence_num] ;

Returning raw data from sys.dm_tran_version_store.
SELECT DB_NAME(DTVS.database_id) AS [Database Name] ,
DTVS.[transaction_sequence_num] ,
DTVS.[version_sequence_num] ,
CASE DTVS.[status]
WHEN 0 THEN ‘1‘
WHEN 1 THEN ‘2‘
END AS [pages] ,
DTVS.[record_length_first_part_in_bytes]
+ DTVS.[record_length_second_part_in_bytes] AS [record length (bytes)]
FROM sys.dm_tran_version_store DTVS
ORDER BY DB_NAME(DTVS.database_id) ,
DTVS.transaction_sequence_num ,
DTVS.version_sequence_num

Storage requirements for the version store
SELECT DB_NAME(DTVS.[database_id]) ,
SUM(DTVS.[record_length_first_part_in_bytes]
+ DTVS.[record_length_second_part_in_bytes]) AS [total store bytes
consumed]
FROM sys.dm_tran_version_store DTVS
GROUP BY DB_NAME(DTVS.[database_id]) ;
Finding the highest-consuming version store record within tempdb.

WITH version_store ( [rowset_id], [bytes consumed] )
AS ( SELECT TOP 1
[rowset_id] ,
SUM([record_length_first_part_in_bytes]
+ [record_length_second_part_in_bytes])
AS [bytes consumed]
FROM sys.dm_tran_version_store
GROUP BY [rowset_id]
ORDER BY SUM([record_length_first_part_in_bytes]
+ [record_length_second_part_in_bytes])
)
SELECT VS.[rowset_id] ,
VS.[bytes consumed] ,
DB_NAME(DTVS.[database_id]) AS [database name] ,
DTASDT.[session_id] AS session_id ,
DES.[login_name] AS [session login] ,
DEST.text AS [session command]
FROM version_store VS
INNER JOIN sys.[dm_tran_version_store] DTVS
ON VS.rowset_id = DTVS.[rowset_id]
INNER JOIN sys.[dm_tran_active_snapshot_database_transactions]
DTASDT
ON DTVS.[transaction_sequence_num] =
DTASDT.[transaction_sequence_num]
INNER JOIN sys.dm_exec_connections DEC
ON DTASDT.[session_id] = DEC.[most_recent_session_id]
INNER JOIN sys.[dm_exec_sessions] DES
ON DEC.[most_recent_session_id] = DES.[session_id]
CROSS APPLY sys.[dm_exec_sql_text](DEC.[most_recent_sql_handle])
DEST ;
Returning raw data from sys.dm_tran_top_version_generators.
SELECT DB_NAME(DTTVG.[database_id]) ,
DTTVG.[rowset_id] ,
DTTVG.[aggregated_record_length_in_bytes]
FROM sys.[dm_tran_top_version_generators] DTTVG
ORDER BY DTTVG.[aggregated_record_length_in_bytes] DESC ;
Querying index use in the AdventureWorks database
SELECT DB_NAME(ddius.[database_id]) AS database_name ,
OBJECT_NAME(ddius.[object_id], DB_ID(‘AdventureWorks‘))
AS [object_name] ,
asi.[name] AS index_name ,
ddius.user_seeks + ddius.user_scans + ddius.user_lookups AS user_reads
FROM sys.dm_db_index_usage_stats ddius
INNER JOIN AdventureWorks.sys.indexes asi
ON ddius.[object_id] = asi.[object_id]
AND ddius.index_id = asi.index_id ;
The combination of object_id and index_id cannot guarantee uniqueness at the instance level.
SELECT DB_NAME(ddius.[database_id]) AS [database_name] ,
ddius.[database_id] ,
ddius.[object_id] ,
ddius.[index_id]
FROM sys.[dm_db_index_usage_stats] ddius
INNER JOIN AdventureWorks.sys.[indexes] asi
ON ddius.[object_id] = asi.[object_id]
AND ddius.[index_id] = asi.[index_id]
Usage stats for indexes that have been used to resolve a query.

SELECT OBJECT_NAME(ddius.[object_id], ddius.database_id) AS [object_name] ,
ddius.index_id ,
ddius.user_seeks ,
ddius.user_scans ,
ddius.user_lookups ,
ddius.user_seeks + ddius.user_scans + ddius.user_lookups
AS user_reads ,
ddius.user_updates AS user_writes ,
ddius.last_user_scan ,
ddius.last_user_update
FROM sys.dm_db_index_usage_stats ddius
WHERE ddius.database_id > 4 -- filter out system tables
AND OBJECTPROPERTY(ddius.object_id, ‘IsUserTable‘) = 1
AND ddius.index_id > 0 -- filter out heaps
ORDER BY ddius.user_scans DESC
Finding unused indexes.
-- List unused indexes
SELECT OBJECT_NAME(i.[object_id]) AS [Table Name] ,
i.name
FROM sys.indexes AS i
INNER JOIN sys.objects AS o ON i.[object_id] = o.[object_id]
WHERE i.index_id NOT IN ( SELECT ddius.index_id
FROM sys.dm_db_index_usage_stats AS ddius
WHERE ddius.[object_id] = i.[object_id]
AND i.index_id = ddius.index_id AND database_id = DB_ID() )
AND o.[type] = ‘U‘
ORDER BY OBJECT_NAME(i.[object_id]) ASC ;
Querying sys.dm_db_index_usage_stats for indexes that are being maintained but not used.

SELECT ‘[‘ + DB_NAME() + ‘].[‘ + su.[name] + ‘].[‘ + o.[name] + ‘]‘
AS [statement] ,
i.[name] AS [index_name] ,
ddius.[user_seeks] + ddius.[user_scans] + ddius.[user_lookups]
AS [user_reads] ,
ddius.[user_updates] AS [user_writes] ,
SUM(SP.rows) AS [total_rows]
FROM sys.dm_db_index_usage_stats ddius
INNER JOIN sys.indexes i ON ddius.[object_id] = i.[object_id]
AND i.[index_id] = ddius.[index_id]
INNER JOIN sys.partitions SP ON ddius.[object_id] = SP.[object_id]
AND SP.[index_id] = ddius.[index_id]
INNER JOIN sys.objects o ON ddius.[object_id] = o.[object_id]
INNER JOIN sys.sysusers su ON o.[schema_id] = su.[UID]
WHERE ddius.[database_id] = DB_ID() -- current database only
AND OBJECTPROPERTY(ddius.[object_id], ‘IsUserTable‘) = 1
AND ddius.[index_id] > 0
GROUP BY su.[name] ,
o.[name] ,
i.[name] ,
ddius.[user_seeks] + ddius.[user_scans] + ddius.[user_lookups] ,
ddius.[user_updates]
HAVING ddius.[user_seeks] + ddius.[user_scans] + ddius.[user_lookups] = 0
ORDER BY ddius.[user_updates] DESC ,
su.[name] ,
o.[name] ,
i.[name ]
Genarage drop index command in SELECT

‘DROP INDEX [‘ + i.[name] + ‘] ON [‘ + su.[name] + ‘].[‘ + o.[name]
+ ‘] WITH ( ONLINE = OFF )‘ AS [drop_command]

How old are the index usage stats?
SELECT DATEDIFF(DAY, sd.crdate, GETDATE()) AS days_history
FROM sys.sysdatabases sd
WHERE sd.[name] = ‘tempdb‘ ;
Finding rarely-used indexes.

-- Potentially inefficient non-clustered indexes (writes > reads)
SELECT OBJECT_NAME(ddius.[object_id]) AS [Table Name] ,
i.name AS [Index Name] ,
i.index_id ,
user_updates AS [Total Writes] ,
user_seeks + user_scans + user_lookups AS [Total Reads] ,
user_updates - ( user_seeks + user_scans + user_lookups )
AS [Difference]
FROM sys.dm_db_index_usage_stats AS ddius WITH ( NOLOCK )
INNER JOIN sys.indexes AS i WITH ( NOLOCK )
ON ddius.[object_id] = i.[object_id]
AND i.index_id = ddius.index_id
WHERE OBJECTPROPERTY(ddius.[object_id], ‘IsUserTable‘) = 1
AND ddius.database_id = DB_ID()
AND user_updates > ( user_seeks + user_scans + user_lookups )
AND i.index_id > 1
ORDER BY [Difference] DESC ,
[Total Writes] DESC ,
[Total Reads] ASC ;
Detailed write information for unused indexes.

SELECT ‘[‘ + DB_NAME() + ‘].[‘ + su.[name] + ‘].[‘ + o.[name] + ‘]‘
AS [statement] ,
i.[name] AS [index_name] ,
ddius.[user_seeks] + ddius.[user_scans] + ddius.[user_lookups]
AS [user_reads] ,
ddius.[user_updates] AS [user_writes] ,
ddios.[leaf_insert_count] ,
ddios.[leaf_delete_count] ,
ddios.[leaf_update_count] ,
ddios.[nonleaf_insert_count] ,
ddios.[nonleaf_delete_count] ,
ddios.[nonleaf_update_count]
FROM sys.dm_db_index_usage_stats ddius
INNER JOIN sys.indexes i ON ddius.[object_id] = i.[object_id]
AND i.[index_id] = ddius.[index_id]
INNER JOIN sys.partitions SP ON ddius.[object_id] = SP.[object_id]
AND SP.[index_id] = ddius.[index_id]
INNER JOIN sys.objects o ON ddius.[object_id] = o.[object_id]
INNER JOIN sys.sysusers su ON o.[schema_id] = su.[UID]
INNER JOIN sys.[dm_db_index_operational_stats](DB_ID(), NULL, NULL,
NULL)
AS ddios
ON ddius.[index_id] = ddios.[index_id] 
AND ddius.[object_id] = ddios.[object_id]
AND SP.[partition_number] = ddios.[partition_number]
AND ddius.[database_id] = ddios.[database_id]
WHERE OBJECTPROPERTY(ddius.[object_id], ‘IsUserTable‘) = 1
AND ddius.[index_id] > 0
AND ddius.[user_seeks] + ddius.[user_scans] + ddius.[user_lookups] = 0
ORDER BY ddius.[user_updates] DESC ,
su.[name] ,
o.[name] ,
i.[name ]
Retrieving locking and blocking details for each index.

SELECT ‘[‘ + DB_NAME(ddios.[database_id]) + ‘].[‘ + su.[name] + ‘].[‘
+ o.[name] + ‘]‘ AS [statement] ,
i.[name] AS ‘index_name‘ ,
ddios.[partition_number] ,
ddios.[row_lock_count] ,
ddios.[row_lock_wait_count] ,
CAST (100.0 * ddios.[row_lock_wait_count]
/ ( ddios.[row_lock_count] ) AS DECIMAL(5, 2)) AS [%_times_blocked] ,
ddios.[row_lock_wait_in_ms] ,
CAST (1.0 * ddios.[row_lock_wait_in_ms]
/ ddios.[row_lock_wait_count] AS DECIMAL(15, 2))
AS [avg_row_lock_wait_in_ms]
FROM sys.dm_db_index_operational_stats(DB_ID(), NULL, NULL, NULL) ddios
INNER JOIN sys.indexes i ON ddios.[object_id] = i.[object_id]
AND i.[index_id] = ddios.[index_id]
INNER JOIN sys.objects o ON ddios.[object_id] = o.[object_id]
INNER JOIN sys.sysusers su ON o.[schema_id] = su.[UID]
WHERE ddios.row_lock_wait_count > 0
AND OBJECTPROPERTY(ddios.[object_id], ‘IsUserTable‘) = 1
AND i.[index_id] > 0
ORDER BY ddios.[row_lock_wait_count] DESC ,
su.[name] ,
o.[name] ,
i.[name ]
Investigating latch waits.
SELECT ‘[‘ + DB_NAME() + ‘].[‘ + OBJECT_SCHEMA_NAME(ddios.[object_id])
+ ‘].[‘ + OBJECT_NAME(ddios.[object_id]) + ‘]‘ AS [object_name] ,
i.[name] AS index_name ,
ddios.page_io_latch_wait_count ,
ddios.page_io_latch_wait_in_ms ,
( ddios.page_io_latch_wait_in_ms / ddios.page_io_latch_wait_count )
AS avg_page_io_latch_wait_in_ms
FROM sys.dm_db_index_operational_stats(DB_ID(), NULL, NULL, NULL) ddios
INNER JOIN sys.indexes i ON ddios.[object_id] = i.[object_id]
AND i.index_id = ddios.index_id
WHERE ddios.page_io_latch_wait_count > 0
AND OBJECTPROPERTY(i.object_id, ‘IsUserTable‘) = 1
ORDER BY ddios.page_io_latch_wait_count DESC ,
avg_page_io_latch_wait_in_ms DESC
Investigating lock escalation.

SELECT OBJECT_NAME(ddios.[object_id], ddios.database_id) AS [object_name] ,
i.name AS index_name ,
ddios.index_id ,
ddios.partition_number ,
ddios.index_lock_promotion_attempt_count ,
ddios.index_lock_promotion_count ,
( ddios.index_lock_promotion_attempt_count
/ ddios.index_lock_promotion_count ) AS percent_success
FROM sys.dm_db_index_operational_stats(DB_ID(), NULL, NULL, NULL) ddios
INNER JOIN sys.indexes i ON ddios.object_id = i.object_id
AND ddios.index_id = i.index_id
WHERE ddios.index_lock_promotion_count > 0
ORDER BY index_lock_promotion_count DESC ;
Indexes associated with lock contention.
SELECT OBJECT_NAME(ddios.object_id, ddios.database_id) AS object_name ,
i.name AS index_name ,
ddios.index_id ,
ddios.partition_number ,
ddios.page_lock_wait_count ,
ddios.page_lock_wait_in_ms ,
CASE WHEN DDMID.database_id IS NULL THEN ‘N‘
ELSE ‘Y‘
END AS missing_index_identified
FROM sys.dm_db_index_operational_stats(DB_ID(), NULL, NULL, NULL) ddios
INNER JOIN sys.indexes i ON ddios.object_id = i.object_id
AND ddios.index_id = i.index_id
LEFT OUTER JOIN ( SELECT DISTINCT
database_id ,
object_id
FROM sys.dm_db_missing_index_details
) AS DDMID ON DDMID.database_id = ddios.database_id
AND DDMID.object_id = ddios.object_id
WHERE ddios.page_lock_wait_in_ms > 0
ORDER BY ddios.page_lock_wait_count DESC ;
Finding beneficial missing indexes.
SELECT user_seeks * avg_total_user_cost * ( avg_user_impact * 0.01 )
AS [index_advantage] ,
dbmigs.last_user_seek ,
dbmid.[statement] AS [Database.Schema.Table] ,
dbmid.equality_columns ,
dbmid.inequality_columns ,
dbmid.included_columns ,
dbmigs.unique_compiles ,
dbmigs.user_seeks ,
dbmigs.avg_total_user_cost ,
dbmigs.avg_user_impact
FROM sys.dm_db_missing_index_group_stats AS dbmigs WITH ( NOLOCK )
INNER JOIN sys.dm_db_missing_index_groups AS dbmig WITH ( NOLOCK )
ON dbmigs.group_handle = dbmig.index_group_handle
INNER JOIN sys.dm_db_missing_index_details AS dbmid WITH ( NOLOCK )
ON dbmig.index_handle = dbmid.index_handle
WHERE dbmid.[database_id] = DB_ID()
ORDER BY index_advantage DESC ;
Investigating fragmented indexes.

SELECT ‘[‘ + DB_NAME() + ‘].[‘ + OBJECT_SCHEMA_NAME(ddips.[object_id],
DB_ID()) + ‘].[‘
+ OBJECT_NAME(ddips.[object_id], DB_ID()) + ‘]‘ AS [statement] ,
i.[name] AS [index_name] ,
ddips.[index_type_desc] ,
ddips.[partition_number] ,
ddips.[alloc_unit_type_desc] ,
ddips.[index_depth] ,
ddips.[index_level] ,
CAST(ddips.[avg_fragmentation_in_percent] AS SMALLINT)
AS [avg_frag_%] ,
CAST(ddips.[avg_fragment_size_in_pages] AS SMALLINT)
AS [avg_frag_size_in_pages] ,
ddips.[fragment_count] ,
ddips.[page_count]
FROM sys.dm_db_index_physical_stats(DB_ID(), NULL,
NULL, NULL, ‘limited‘) ddips
INNER JOIN sys.[indexes] i ON ddips.[object_id] = i.[object_id]
AND ddips.[index_id] = i.[index_id]
WHERE ddips.[avg_fragmentation_in_percent] > 15
AND ddips.[page_count] > 500
ORDER BY ddips.[avg_fragmentation_in_percent] ,
OBJECT_NAME(ddips.[object_id], DB_ID()) ,
i.[name ]
Number of rows in clustered tables and heaps.

SELECT object_schema_name(ddps.object_id) +
‘.‘ + OBJECT_NAME(ddps.object_id) AS name ,
SUM(ddps.row_count) AS row_count
FROM sys.dm_db_partition_stats AS ddps
JOIN sys.indexes ON indexes.object_id = ddps.object_id
AND indexes.index_id = ddps.index_id
WHERE indexes.type_desc IN ( ‘CLUSTERED‘, ‘HEAP‘ )
and objectproperty(ddps.object_id,‘IsMSShipped‘) = 0
GROUP BY ddps.object_id
Creating a three-partition salesOrder table.

CREATE PARTITION FUNCTION PFdateRange (SMALLDATETIME)
AS RANGE LEFT FOR VALUES (‘20020101‘,‘20030101‘) ;
GO
CREATE PARTITION SCHEME PSdateRange
AS PARTITION PFdateRange ALL TO ( [PRIMARY] )
GO
CREATE TABLE salesOrder
(
salesOrderId INT ,
customerId INT ,
orderAmount DECIMAL(10, 2) ,
orderDate SMALLDATETIME ,
CONSTRAINT PKsalesOrder PRIMARY KEY NONCLUSTERED ( salesOrderId )
ON [Primary] ,
CONSTRAINT AKsalesOrder UNIQUE CLUSTERED ( salesOrderId, orderDate )
)
--the ON clause causes this clustered table to be partitioned by orderDate
--using the partition function/scheme
ON PSdateRange(orderDate)
GO
--Generate some random data
INSERT INTO salesOrder
SELECT SalesOrderId ,
CustomerId ,
TotalDue ,
OrderDate
FROM AdventureWorks.Sales.SalesOrderHeader
Number of rows in each object, per partition.
SELECT indexes.name ,
indexes.type_desc ,
dps.row_count AS row_count ,
partition_id
FROM sys.dm_db_partition_stats AS dps
JOIN sys.indexes ON indexes.object_id = dps.object_id
AND indexes.index_id = dps.index_id
WHERE OBJECT_ID(‘salesOrder‘) = dps.object_id
Physical characteristics of each partition

SELECT OBJECT_NAME(indexes.object_id) AS Object_Name ,
ddps.index_id AS Index_ID ,
ddps.partition_number ,
ddps.row_count ,
ddps.used_page_count ,
ddps.in_row_reserved_page_count ,
ddps.lob_reserved_page_count ,
CASE pf.boundary_value_on_right
WHEN 1 THEN ‘less than‘
ELSE ‘less than or equal to‘
END AS comparison ,
value
FROM sys.dm_db_partition_stats ddps
JOIN sys.indexes ON ddps.object_id = indexes.object_id
AND ddps.index_id = indexes.index_id
JOIN sys.partition_schemes ps
ON ps.data_space_id = indexes.data_space_id
JOIN sys.partition_functions pf ON pf.function_id = ps.function_id
LEFT OUTER JOIN sys.partition_range_values prv
ON pf.function_id = prv.function_id
AND ddps.partition_number = prv.boundary_id
WHERE OBJECT_NAME(ddps.object_id) = ‘salesOrder ‘
AND ddps.index_id IN ( 0, 1 ) --CLUSTERED table or HEAP
Fragmentation statistics for the testClusteredIdentity clustered table
SELECT avg_fragmentation_in_percent AS avgFragPct ,
fragment_count AS fragCount ,
avg_fragment_size_in_pages AS avgFragSize
FROM sys.dm_db_index_physical_stats(DB_ID(), NULL, NULL, NULL, ‘DETAILED‘)
WHERE index_type_desc = ‘CLUSTERED INDEX‘
AND index_level = 0 -- the other levels are the index pages
AND OBJECT_NAME(object_id) = ‘testClusteredIdentity‘
Fragmentation statistics for testHeap.

SELECT avg_fragmentation_in_percent AS avgFragPct ,
fragment_count AS fragCount ,
avg_fragment_size_in_pages AS avgFragSize ,
forwarded_record_count AS forwardPointers
FROM sys.dm_db_index_physical_stats(DB_ID(), NULL, NULL, NULL, ‘DETAILED‘)
WHERE index_type_desc = ‘HEAP‘
AND index_level = 0 -- the other levels are the index pages
AND OBJECT_NAME(object_id) = ‘testHeap‘
Capturing baseline disk I/O statistics from sys.dm_io_virtual_file_stats in a temporary table.

SELECT DB_NAME(mf.database_id) AS databaseName ,
mf.physical_name ,
divfs.num_of_reads ,
divfs.num_of_bytes_read ,
divfs.io_stall_read_ms ,
divfs.num_of_writes ,
divfs.num_of_bytes_written ,
divfs.io_stall_write_ms ,
divfs.io_stall ,
size_on_disk_bytes ,
GETDATE() AS baselineDate
INTO #baseline
FROM sys.dm_io_virtual_file_stats(NULL, NULL) AS divfs
JOIN sys.master_files AS mf ON mf.database_id = divfs.database_id
AND mf.file_id = divfs.file_id
Querying the #baseline temporary table.
SELECT physical_name ,
num_of_reads ,
num_of_bytes_read ,
io_stall_read_ms
FROM #baseline
WHERE databaseName = ‘DatabaseName‘
Capturing 10 seconds of disk I/O statistics, since the baseline measurement.

WITH currentLine
AS ( SELECT DB_NAME(mf.database_id) AS databaseName ,
mf.physical_name ,
num_of_reads ,
num_of_bytes_read ,
io_stall_read_ms ,
num_of_writes ,
num_of_bytes_written ,
io_stall_write_ms ,
io_stall ,
size_on_disk_bytes ,
GETDATE() AS currentlineDate
FROM sys.dm_io_virtual_file_stats(NULL, NULL) AS divfs
JOIN sys.master_files AS mf
ON mf.database_id = divfs.database_id
AND mf.file_id = divfs.file_id
)
SELECT currentLine.databaseName ,
LEFT(currentLine.physical_name, 1) AS drive ,
currentLine.physical_name ,
DATEDIFF(millisecond,baseLineDate,currentLineDate) AS elapsed_ms,
currentLine.io_stall - #baseline.io_stall AS io_stall_ms ,
currentLine.io_stall_read_ms - #baseline.io_stall_read_ms
AS io_stall_read_ms ,
currentLine.io_stall_write_ms - #baseline.io_stall_write_ms
AS io_stall_write_ms ,
currentLine.num_of_reads - #baseline.num_of_reads AS num_of_reads ,
currentLine.num_of_bytes_read - #baseline.num_of_bytes_read
AS num_of_bytes_read ,
currentLine.num_of_writes - #baseline.num_of_writes AS num_of_writes ,
currentLine.num_of_bytes_written - #baseline.num_of_bytes_written
AS num_of_bytes_written
FROM currentLine
INNER JOIN #baseline ON #baseLine.databaseName = currentLine.databaseName
AND #baseLine.physical_name = currentLine.physical_name
WHERE #baseline.databaseName = ‘DatabaseName‘
Returning pending I/O requests.

SELECT mf.physical_name ,
dipir.io_pending ,
dipir.io_pending_ms_ticks
FROM sys.dm_io_pending_io_requests AS dipir
JOIN sys.dm_io_virtual_file_stats(NULL, NULL) AS divfs
ON dipir.io_handle = divfs.file_handle
JOIN sys.master_files AS mf ON divfs.database_id = mf.database_id
AND divfs.file_id = mf.file_id
ORDER BY dipir.io_pending , --Show I/O completed by the OS first
dipir.io_pending_ms_ticks DESC
The read:write ratio, by database, for amount of data transferred.

--uses a LIKE comparison to only include desired databases, rather than
--using the database_id parameter of sys.dm_io_virtual_file_stats
--if you have a rather large number of databases, this may not be the
--optimal way to execute the query, but this gives you flexibility
--to look at multiple databases simultaneously.
DECLARE @databaseName SYSNAME
SET @databaseName = ‘%‘
--‘%‘ gives all databases
SELECT CAST(SUM(num_of_bytes_read) AS DECIMAL)
/ ( CAST(SUM(num_of_bytes_written) AS DECIMAL)
+ CAST(SUM(num_of_bytes_read) AS DECIMAL) ) AS RatioOfReads ,
CAST(SUM(num_of_bytes_written) AS DECIMAL)
/ ( CAST(SUM(num_of_bytes_written) AS DECIMAL)
+ CAST(SUM(num_of_bytes_read) AS DECIMAL) ) AS RatioOfWrites ,
SUM(num_of_bytes_read) AS TotalBytesRead ,
SUM(num_of_bytes_written) AS TotalBytesWritten
FROM sys.dm_io_virtual_file_stats(NULL, NULL) AS divfs
WHERE DB_NAME(database_id) LIKE @databaseName
The read:write ratio, by drive, for amount of data transferred.

DECLARE @databaseName SYSNAME
SET @databaseName = ‘%‘
--‘%‘ gives all databases
SELECT LEFT(physical_name, 1) AS drive ,
CAST(SUM(num_of_bytes_read) AS DECIMAL)
/ ( CAST(SUM(num_of_bytes_written) AS DECIMAL)
+ CAST(SUM(num_of_bytes_read) AS DECIMAL) ) AS RatioOfReads ,
CAST(SUM(num_of_bytes_written) AS DECIMAL)
/ ( CAST(SUM(num_of_bytes_written) AS DECIMAL)
+ CAST(SUM(num_of_bytes_read) AS DECIMAL) ) AS RatioOfWrites ,
SUM(num_of_bytes_read) AS TotalBytesRead ,
SUM(num_of_bytes_written) AS TotalBytesWritten
FROM sys.dm_io_virtual_file_stats(NULL, NULL) AS divfs
JOIN sys.master_files AS mf ON mf.database_id = divfs.database_id
AND mf.file_id = divfs.file_id
WHERE DB_NAME(divfs.database_id) LIKE @databaseName
GROUP BY LEFT(mf.physical_name, 1)
The read:write ratio, by database, for number of read/write operations.

DECLARE @databaseName SYSNAME
SET @databaseName = ‘BusyDatabase‘
--obviously not the real name
--‘%‘ gives all databases
SELECT CAST(SUM(num_of_reads) AS DECIMAL)
/ ( CAST(SUM(num_of_writes) AS DECIMAL)
+ CAST(SUM(num_of_reads) AS DECIMAL) ) AS RatioOfReads ,
CAST(SUM(num_of_writes) AS DECIMAL)
/ ( CAST(SUM(num_of_reads) AS DECIMAL)
+ CAST(SUM(num_of_writes) AS DECIMAL) ) AS RatioOfWrites ,
SUM(num_of_reads) AS TotalReadOperations ,
SUM(num_of_writes) AS TotalWriteOperations
FROM sys.dm_io_virtual_file_stats(NULL, NULL) AS divfs
WHERE DB_NAME(database_id) LIKE @databaseName
Read:write ratio for all objects in a given database.

DECLARE @databaseName SYSNAME
SET @databaseName = ‘BusyDatabase‘ --obviously not the real name
--‘%‘ gives all databases
SELECT CASE
WHEN ( SUM(user_updates + user_seeks + user_scans + user_lookups) = 0 )
THEN NULL
ELSE ( CAST(SUM(user_seeks + user_scans + user_lookups)
AS DECIMAL)
/ CAST(SUM(user_updates + user_seeks + user_scans
+ user_lookups) AS DECIMAL) )
END AS RatioOfReads ,
CASE
WHEN ( SUM(user_updates + user_seeks + user_scans + user_lookups) = 0 )
THEN NULL
ELSE ( CAST(SUM(user_updates) AS DECIMAL)
/ CAST(SUM(user_updates + user_seeks + user_scans
+ user_lookups) AS DECIMAL) )
END AS RatioOfWrites ,
SUM(user_updates + user_seeks + user_scans + user_lookups)
AS TotalReadOperations ,
SUM(user_updates) AS TotalWriteOperations
FROM sys.dm_db_index_usage_stats AS ddius
WHERE DB_NAME(database_id) LIKE @databaseName
Read:write ratio per object.

--only works in the context of the database due to sys.indexes usage
USE BusyDatabase
--obviously not the real name
SELECT OBJECT_NAME(ddius.object_id) AS object_name ,
CASE
WHEN ( SUM(user_updates + user_seeks + user_scans + user_lookups) = 0 )
THEN NULL
ELSE ( CAST(SUM(user_seeks + user_scans + user_lookups) AS DECIMAL)
/ CAST(SUM(user_updates + user_seeks + user_scans
+ user_lookups) AS DECIMAL) )
END AS RatioOfReads ,
CASE
WHEN ( SUM(user_updates + user_seeks + user_scans + user_lookups) = 0 )
THEN NULL
ELSE ( CAST(SUM(user_updates) AS DECIMAL)
/ CAST(SUM(user_updates + user_seeks + user_scans
+ user_lookups) AS DECIMAL) )
END AS RatioOfWrites ,
SUM(user_updates + user_seeks + user_scans + user_lookups)
AS TotalReadOperations ,
SUM(user_updates) AS TotalWriteOperations
FROM sys.dm_db_index_usage_stats AS ddius
JOIN sys.indexes AS i ON ddius.object_id = i.object_id
AND ddius.index_id = i.index_id
WHERE i.type_desc IN ( ‘CLUSTERED‘, ‘HEAP‘ ) --only works in Current db
GROUP BY ddius.object_id
ORDER BY OBJECT_NAME(ddius.object_id)
An overview of tempdb utilization.

SELECT mf.physical_name ,
mf.size AS entire_file_page_count ,
dfsu.version_store_reserved_page_count ,
dfsu.unallocated_extent_page_count ,
dfsu.user_object_reserved_page_count ,
dfsu.internal_object_reserved_page_count ,
dfsu.mixed_extent_page_count
FROM sys.dm_db_file_space_usage dfsu
JOIN sys.master_files AS mf ON mf.database_id = dfsu.database_id
AND mf.file_id = dfsu.file_id
tempdb file size and version store usage.

SELECT SUM(mf.size) AS entire_page_count ,
SUM(dfsu.version_store_reserved_page_count) AS version_store_reserved_page_
count
FROM sys.dm_db_file_space_usage dfsu
JOIN sys.master_files AS mf ON mf.database_id = dfsu.database_id
AND mf.file_id = dfsu.file_id
Resetting the wait statistics.
DBCC SQLPERF (‘sys.dm_os_wait_stats‘, CLEAR);
The most common waits.

SELECT TOP 3
wait_type ,
waiting_tasks_count ,
wait_time_ms / 1000.0 AS wait_time_sec ,
CASE WHEN waiting_tasks_count = 0 THEN NULL
ELSE wait_time_ms / 1000.0 / waiting_tasks_count
END AS avg_wait_time_sec ,
max_wait_time_ms / 1000.0 AS max_wait_time_sec ,
( wait_time_ms - signal_wait_time_ms ) / 1000.0 AS resource_wait_time_sec
FROM sys.dm_os_wait_stats
WHERE wait_type NOT IN --tasks that are actually good or expected
--to be waited on
( ‘CLR_SEMAPHORE‘, ‘LAZYWRITER_SLEEP‘, ‘RESOURCE_QUEUE‘, ‘SLEEP_TASK‘,
‘SLEEP_SYSTEMTASK‘, ‘WAITFOR‘ )
ORDER BY waiting_tasks_count DESC
Report on top resource waits.

-- Isolate top waits for server instance since last restart
-- or statistics clear
WITH Waits
AS ( SELECT wait_type ,
wait_time_ms / 1000. AS wait_time_sec ,
100. * wait_time_ms / SUM(wait_time_ms) OVER ( ) AS pct ,
ROW_NUMBER() OVER ( ORDER BY wait_time_ms DESC ) AS rn
FROM sys.dm_os_wait_stats
WHERE wait_type NOT IN ( ‘CLR_SEMAPHORE‘, ‘LAZYWRITER_SLEEP‘,
‘RESOURCE_QUEUE‘, ‘SLEEP_TASK‘,
‘SLEEP_SYSTEMTASK‘,
‘SQLTRACE_BUFFER_FLUSH‘, ‘WAITFOR‘,
‘LOGMGR_QUEUE‘, ‘CHECKPOINT_QUEUE‘ )
)
SELECT wait_type ,
CAST(wait_time_sec AS DECIMAL(12, 2)) AS wait_time_sec ,
CAST(pct AS DECIMAL(12, 2)) AS wait_time_percentage
FROM Waits
WHERE pct > 1
ORDER BY wait_time_sec DESC
Seeking out locking waits.

SELECT wait_type ,
waiting_tasks_count ,
wait_time_ms ,
max_wait_time_ms
FROM sys.dm_os_wait_stats
WHERE wait_type LIKE ‘LCK%‘
AND Waiting_tasks_count > 0
ORDER BY waiting_tasks_count DESC
Is there any CPU pressure?

-- Total waits are wait_time_ms (high signal waits indicates CPU pressure)
SELECT CAST(100.0 * SUM(signal_wait_time_ms) / SUM(wait_time_ms)
AS NUMERIC(20,2)) AS [%signal (cpu) waits] ,
CAST(100.0 * SUM(wait_time_ms - signal_wait_time_ms)
/ SUM(wait_time_ms) AS NUMERIC(20, 2)) AS [%resource waits]
FROM sys.dm_os_wait_stats ;
Returning a list of PerfMon counter types.

SELECT DISTINCT
cntr_type
FROM sys.dm_os_performance_counters
ORDER BY cntr_type
Returning the values of directly usable PerfMon counters.

DECLARE @PERF_COUNTER_LARGE_RAWCOUNT INT
SELECT @PERF_COUNTER_LARGE_RAWCOUNT = 65792
SELECT object_name ,
counter_name ,
instance_name ,
cntr_value
FROM sys.dm_os_performance_counters
WHERE cntr_type = @PERF_COUNTER_LARGE_RAWCOUNT
ORDER BY object_name ,
counter_name ,
instance_name
Monitoring changes in the size of the transaction log.

--the default instance reports as SQLServer, but other
--instances as MSSQL$InstanceName
DECLARE @object_name SYSNAME
SET @object_name = CASE WHEN @@servicename = ‘MSSQLSERVER‘ THEN ‘SQLServer‘
ELSE ‘MSSQL$‘ + @@serviceName
END + ‘:Databases‘
DECLARE @PERF_COUNTER_LARGE_RAWCOUNT INT
SELECT @PERF_COUNTER_LARGE_RAWCOUNT = 65792
SELECT object_name ,
counter_name ,
instance_name ,
cntr_value
FROM sys.dm_os_performance_counters
WHERE cntr_type = @PERF_COUNTER_LARGE_RAWCOUNT
AND object_name = @object_name
AND counter_name IN ( ‘Log Growths‘, ‘Log Shrinks‘ )
AND cntr_value > 0
ORDER BY object_name ,
counter_name ,
instance_name
Which deprecated features are still in use?
DECLARE @object_name SYSNAME
SET @object_name = CASE WHEN @@servicename = ‘MSSQLSERVER‘ THEN ‘SQLServer‘
ELSE ‘MSSQL$‘ + @@serviceName
END + ‘:Deprecated Features‘
DECLARE @PERF_COUNTER_LARGE_RAWCOUNT INT
SELECT @PERF_COUNTER_LARGE_RAWCOUNT = 65792
SELECT object_name ,
counter_name ,
instance_name ,
cntr_value
FROM sys.dm_os_performance_counters
WHERE cntr_type = @PERF_COUNTER_LARGE_RAWCOUNT
AND object_name = @object_name
AND cntr_value > 0
Returning the values of ratio PerfMon counters.

DECLARE @PERF_LARGE_RAW_FRACTION INT ,
@PERF_LARGE_RAW_BASE INT
SELECT @PERF_LARGE_RAW_FRACTION = 537003264 ,
@PERF_LARGE_RAW_BASE = 1073939712
SELECT dopc_fraction.object_name ,
dopc_fraction.instance_name ,
dopc_fraction.counter_name ,
--when divisor is 0, return I return NULL to indicate
--divide by 0/no values captured
CAST(dopc_fraction.cntr_value AS FLOAT)
/ CAST(CASE dopc_base.cntr_value
WHEN 0 THEN NULL
ELSE dopc_base.cntr_value
END AS FLOAT) AS cntr_value
FROM sys.dm_os_performance_counters AS dopc_base
JOIN sys.dm_os_performance_counters AS dopc_fraction
ON dopc_base.cntr_type = @PERF_LARGE_RAW_BASE
AND dopc_fraction.cntr_type = @PERF_LARGE_RAW_FRACTION
AND dopc_base.object_name = dopc_fraction.object_name
AND dopc_base.instance_name = dopc_fraction.instance_name
AND ( REPLACE(dopc_base.counter_name,
‘base‘, ‘‘) = dopc_fraction.counter_name
--Worktables From Cache has "odd" name where
--Ratio was left off
OR REPLACE(dopc_base.counter_name,
‘base‘, ‘‘) = ( REPLACE(dopc_fraction.counter_name,
‘ratio‘, ‘‘) )
)
ORDER BY dopc_fraction.object_name ,
dopc_fraction.instance_name ,
dopc_fraction.counter_name
Returning the current value for the buffer cache hit ratio.

DECLARE @object_name SYSNAME
SET @object_name = CASE WHEN @@servicename = ‘MSSQLSERVER‘ THEN ‘SQLServer‘
ELSE ‘MSSQL$‘ + @@serviceName
END + ‘:Buffer Manager‘
DECLARE
@PERF_LARGE_RAW_FRACTION INT ,
@PERF_LARGE_RAW_BASE INT
SELECT @PERF_LARGE_RAW_FRACTION = 537003264 ,
@PERF_LARGE_RAW_BASE = 1073939712
SELECT dopc_fraction.object_name ,
dopc_fraction.instance_name ,
dopc_fraction.counter_name ,
--when divisor is 0, return I return NULL to indicate
--divide by 0/no values captured
CAST(dopc_fraction.cntr_value AS FLOAT)
/ CAST(CASE dopc_base.cntr_value
WHEN 0 THEN NULL
ELSE dopc_base.cntr_value
END AS FLOAT) AS cntr_value
FROM sys.dm_os_performance_counters AS dopc_base
JOIN sys.dm_os_performance_counters AS dopc_fraction
ON dopc_base.cntr_type = @PERF_LARGE_RAW_BASE
AND dopc_fraction.cntr_type = @PERF_LARGE_RAW_FRACTION
AND dopc_base.object_name = dopc_fraction.object_name
AND dopc_base.instance_name = dopc_fraction.instance_name
AND ( REPLACE(dopc_base.counter_name,
‘base‘, ‘‘) = dopc_fraction.counter_name
--Worktables From Cache has "odd" name where
--Ratio was left off
OR REPLACE(dopc_base.counter_name,
‘base‘, ‘‘) = ( REPLACE(dopc_fraction.counter_name,
‘ratio‘, ‘‘) )
)
WHERE dopc_fraction.object_name = @object_name
AND dopc_fraction.instance_name = ‘‘
AND dopc_fraction.counter_name = ‘Buffer cache hit ratio‘
ORDER BY dopc_fraction.object_name ,
dopc_fraction.instance_name ,
dopc_fraction.counter_name

Returning the values of "per second average" PerfMon counters.

DECLARE @PERF_COUNTER_BULK_COUNT INT
SELECT @PERF_COUNTER_BULK_COUNT = 272696576
--Holds initial state
DECLARE @baseline TABLE
(
object_name NVARCHAR(256) ,
counter_name NVARCHAR(256) ,
instance_name NVARCHAR(256) ,
cntr_value BIGINT ,
cntr_type INT ,
time DATETIME DEFAULT ( GETDATE() )
)
DECLARE @current TABLE
(
object_name NVARCHAR(256) ,
counter_name NVARCHAR(256) ,
instance_name NVARCHAR(256) ,
cntr_value BIGINT ,
cntr_type INT ,
time DATETIME DEFAULT ( GETDATE() )
)
--capture the initial state of bulk counters
INSERT INTO @baseline
( object_name ,
counter_name ,
instance_name ,
cntr_value ,
cntr_type
)
SELECT object_name ,
counter_name ,
instance_name ,
cntr_value ,
cntr_type
FROM sys.dm_os_performance_counters AS dopc
WHERE cntr_type = @PERF_COUNTER_BULK_COUNT
WAITFOR DELAY ‘00:00:05‘ --the code will work regardless of delay chosen
--get the followon state of the counters
INSERT INTO @current
( object_name ,
counter_name ,
instance_name ,
cntr_value ,
cntr_type
)
SELECT object_name ,
counter_name ,
instance_name ,
cntr_value ,
cntr_type
FROM sys.dm_os_performance_counters AS dopc
WHERE cntr_type = @PERF_COUNTER_BULK_COUNT
SELECT dopc.object_name ,
dopc.instance_name ,
dopc.counter_name ,
--ms to second conversion factor
1000 *
--current value less the previous value
( ( dopc.cntr_value - prev_dopc.cntr_value )
--divided by the number of milliseconds that pass
--casted as float to get fractional results. Float
--lets really big or really small numbers to work
/ CAST(DATEDIFF(ms, prev_dopc.time, dopc.time) AS FLOAT) )
AS cntr_value
--simply join on the names of the counters
FROM @current AS dopc
JOIN @baseline AS prev_dopc ON prev_dopc.object_name = dopc.object_name
AND prev_dopc.instance_name = dopc.instance_name
AND prev_dopc.counter_name = dopc.counter_name
WHERE dopc.cntr_type = @PERF_COUNTER_BULK_COUNT
AND 1000 * ( ( dopc.cntr_value - prev_dopc.cntr_value )
/ CAST(DATEDIFF(ms, prev_dopc.time, dopc.time) AS FLOAT) )
/* default to only showing non-zero values */ <> 0
ORDER BY dopc.object_name ,
dopc.instance_name ,
dopc.counter_name

Returning the values for the "average number of operations" PerfMon counters.

DECLARE @PERF_AVERAGE_BULK INT ,
@PERF_LARGE_RAW_BASE INT
SELECT @PERF_AVERAGE_BULK = 1073874176 ,
@PERF_LARGE_RAW_BASE = 1073939712
SELECT dopc_avgBulk.object_name ,
dopc_avgBulk.instance_name ,
dopc_avgBulk.counter_name ,
CAST(dopc_avgBulk.cntr_value AS FLOAT)
--when divisor is 0, return NULL to indicate
--divide by 0
/ CAST(CASE dopc_base.cntr_value
WHEN 0 THEN NULL
ELSE dopc_base.cntr_value
END AS FLOAT) AS cntr_value
FROM sys.dm_os_performance_counters dopc_base
JOIN sys.dm_os_performance_counters dopc_avgBulk
ON dopc_base.cntr_type = @PERF_LARGE_RAW_BASE
AND dopc_avgBulk.cntr_type = @PERF_AVERAGE_BULK
AND dopc_base.object_name = dopc_avgBulk.object_name
AND dopc_base.instance_name = dopc_avgBulk.instance_name
--Average Wait Time has (ms) in name,
--so it has handled "special"
AND ( REPLACE(dopc_base.counter_name,
‘base‘, ‘‘) = dopc_avgBulk.counter_name
OR REPLACE(dopc_base.counter_name,
‘base‘, ‘‘) = REPLACE(dopc_avgBulk.counter_name,
‘(ms)‘, ‘‘)
)
ORDER BY dopc_avgBulk.object_name ,
dopc_avgBulk.instance_name ,
dopc_avgBulk.counter_name

CPU configuration details.

-- Hardware information from SQL Server 2008
-- (Cannot distinguish between HT and multi-core)
SELECT cpu_count AS [Logical CPU Count] ,
hyperthread_ratio AS [Hyperthread Ratio] ,
cpu_count / hyperthread_ratio AS [Physical CPU Count] ,
physical_memory_in_bytes / 1048576 AS [Physical Memory (MB)] ,
sqlserver_start_time
FROM sys.dm_os_sys_info ;

Interrogating memory configuration.

--Determine if this is a 32- or 64-bit SQL Server edition
DECLARE @ServerAddressing AS TINYINT
SELECT @serverAddressing = CASE WHEN CHARINDEX(‘64‘,
CAST(SERVERPROPERTY(‘Edition‘)
AS VARCHAR(100))) > 0
THEN 64
ELSE 32
END ;
SELECT cpu_count / hyperthread_ratio AS SocketCount ,
physical_memory_in_bytes / 1024 / 1024 AS physical_memory_mb ,
virtual_memory_in_bytes / 1024 / 1024 AS sql_max_virtual_memory_mb ,
-- same with other bpool columns as they are page oriented.
-- Multiplying by 8 takes it to 8K, then / 1024 to convert to mb
bpool_committed * 8 / 1024 AS buffer_pool_committed_mb ,
--64 bit OS does not have limitations with addressing as 32 did
CASE WHEN @serverAddressing = 32
THEN CASE WHEN virtual_memory_in_bytes / 1024 /
( 2048 * 1024 ) < 1
THEN ‘off‘
ELSE ‘on‘
END
ELSE ‘N/A on 64 bit‘
END AS [/3GB switch]
FROM sys.dm_os_sys_info

Investigating scheduler activity.

-- Get Avg task count and Avg runnable task count
SELECT AVG(current_tasks_count) AS [Avg Task Count] ,
AVG(runnable_tasks_count) AS [Avg Runnable Task Count]
FROM sys.dm_os_schedulers
WHERE scheduler_id < 255
AND [status] = ‘VISIBLE ONLINE‘ ;

Investigating potential disk I/O or CPU pressure.

SELECT scheduler_id ,
cpu_id ,
Status ,
is_online ,
is_idle ,
current_tasks_count ,
runnable_tasks_count ,
current_workers_count ,
active_workers_count ,
work_queue_count ,
pending_disk_io_count ,
load_factor
FROM sys.dm_os_schedulers
WHERE scheduler_id < 255
AND runnable_tasks_count > 0
-- AND pending_disk_io_count > 0

Are there sufficient worker threads for the workload?

SELECT AVG(work_queue_count)
FROM sys.dm_os_schedulers
WHERE status = ‘VISIBLE ONLINE‘
Investigating context switching.
SELECT scheduler_id ,
preemptive_switches_count ,
context_switches_count ,
idle_switches_count ,
failed_to_create_worker
FROM sys.dm_os_schedulers
WHERE scheduler_id < 255
Is NUMA enabled?
-- Is NUMA enabled
SELECT CASE COUNT(DISTINCT parent_node_id)
WHEN 1 THEN ‘NUMA disabled‘
ELSE ‘NUMA enabled‘
END
FROM sys.dm_os_schedulers
WHERE parent_node_id <> 32 ;

Recent CPU utilization.

-- Get CPU Utilization History for last 30 minutes (in one minute intervals)
-- This version works with SQL Server 2008 and SQL Server 2008 R2 only
DECLARE @ts_now BIGINT = ( SELECT cpu_ticks / ( cpu_ticks / ms_ticks )
FROM sys.dm_os_sys_info
) ;
SELECT TOP ( 30 )
SQLProcessUtilization AS [SQL Server Process CPU Utilization] ,
SystemIdle AS [System Idle Process] ,
100 - SystemIdle – SQLProcessUtilization
AS [Other Process CPU Utilization] ,
DATEADD(ms, -1 * ( @ts_now - [timestamp] ), GETDATE())
AS [Event Time]
FROM ( SELECT record.value(‘(./Record/@id)[1]‘, ‘int‘) AS record_id ,
record.value(‘(./Record/SchedulerMonitorEvent/
SystemHealth/SystemIdle)[1]‘, ‘int‘)
AS [SystemIdle] ,
record.value(‘(./Record/SchedulerMonitorEvent/
SystemHealth/ProcessUtilization)[1]‘,
‘int‘)
AS [SQLProcessUtilization] ,
[timestamp]
FROM ( SELECT [timestamp] ,
CONVERT(XML, record) AS [record]
FROM sys.dm_os_ring_buffers
WHERE ring_buffer_type =
N‘RING_BUFFER_SCHEDULER_MONITOR‘
AND record LIKE N‘%<SystemHealth>%‘
) AS x
) AS y
ORDER BY record_id DESC ;
System memory usage.
SELECT total_physical_memory_kb / 1024 AS total_physical_memory_mb ,
available_physical_memory_kb / 1024 AS available_physical_memory_mb ,
total_page_file_kb / 1024 AS total_page_file_mb ,
available_page_file_kb / 1024 AS available_page_file_mb ,
system_memory_state_desc
FROM sys.dm_os_sys_memory

Memory usage by the SQL Server process.

SELECT physical_memory_in_use_kb ,
virtual_address_space_committed_kb ,
virtual_address_space_available_kb ,
page_fault_count ,
process_physical_memory_low ,
process_virtual_memory_low
FROM sys.dm_os_process_memory

Memory allocation in the buffer pool.

-- Get total buffer usage by database
SELECT DB_NAME(database_id) AS [Database Name] ,
COUNT(*) * 8 / 1024.0 AS [Cached Size (MB)]
FROM sys.dm_os_buffer_descriptors
WHERE database_id > 4 -- exclude system databases
AND database_id <> 32767 -- exclude ResourceDB
GROUP BY DB_NAME(database_id)
ORDER BY [Cached Size (MB)] DESC ;
-- Breaks down buffers by object (table, index) in the buffer pool
SELECT OBJECT_NAME(p.[object_id]) AS [ObjectName] ,
p.index_id ,
COUNT(*) / 128 AS [Buffer size(MB)] ,
COUNT(*) AS [Buffer_count]
FROM sys.allocation_units AS a
INNER JOIN sys.dm_os_buffer_descriptors
AS b ON a.allocation_unit_id = b.allocation_unit_id
INNER JOIN sys.partitions AS p ON a.container_id = p.hobt_id
WHERE b.database_id = DB_ID()
AND p.[object_id] > 100 -- exclude system objects
GROUP BY p.[object_id] ,
p.index_id
ORDER BY buffer_count DESC ;

Buffer pool usage.

-- Buffer Pool Usage for instance
SELECT TOP(20) [type], SUM(single_pages_kb) AS [SPA Mem, Kb]
FROM sys.dm_os_memory_clerks
GROUP BY [type]
ORDER BY SUM(single_pages_kb) DESC;

Which queries have requested, or have had to wait for, large memory grants?

-- Shows the memory required by both running (non-null grant_time)
-- and waiting queries (null grant_time)
-- SQL Server 2008 version
SELECT DB_NAME(st.dbid) AS [DatabaseName] ,
mg.requested_memory_kb ,
mg.ideal_memory_kb ,
mg.request_time ,
mg.grant_time ,
mg.query_cost ,
mg.dop ,
st.[text]
FROM sys.dm_exec_query_memory_grants AS mg
CROSS APPLY sys.dm_exec_sql_text(plan_handle) AS st
WHERE mg.request_time < COALESCE(grant_time, ‘99991231‘)
ORDER BY mg.requested_memory_kb DESC ;
-- Shows the memory required by both running (non-null grant_time)
-- and waiting queries (null grant_time)
-- SQL Server 2005 version
SELECT DB_NAME(st.dbid) AS [DatabaseName] ,
mg.requested_memory_kb ,
mg.request_time ,
mg.grant_time ,
mg.query_cost ,
mg.dop ,
st.[text]
FROM sys.dm_exec_query_memory_grants AS mg
CROSS APPLY sys.dm_exec_sql_text(plan_handle) AS st
WHERE mg.request_time < COALESCE(grant_time, ‘99991231‘)
ORDER BY mg.requested_memory_kb DESC ;

Returning the cache counters.

SELECT type ,
name ,
single_pages_kb ,
multi_pages_kb ,
single_pages_in_use_kb ,
multi_pages_in_use_kb ,
entries_count ,
entries_in_use_count
FROM sys.dm_os_memory_cache_counters
ORDER BY type,name;

Investigating the use of the plan cache.

SELECT name ,
type ,
entries_count ,
entries_in_use_count
FROM sys.dm_os_memory_cache_counters
WHERE type IN ( ‘CACHESTORE_SQLCP‘, ‘CACHESTORE_OBJCP‘ )
--ad hoc plans and object plans
ORDER BY name ,
type

Investigating plan reuse counts.

--in a different connection, execute this all at once:
USE tempdb
go
CREATE PROCEDURE test
AS
WAITFOR DELAY ‘00:00:30‘
SELECT *
FROM sys.sysobjects
go
EXECUTE test

Resetting the latch statistics.

DBCC SQLPERF (‘sys.dm_os_latch_stats‘, CLEAR);

Seeking out latch waits.

SELECT latch_class ,
waiting_requests_count AS waitCount ,
wait_time_ms AS waitTime ,
max_wait_time_ms AS maxWait
FROM sys.dm_os_latch_stats
ORDER BY wait_time_ms DESC
Finding the top ten CPU-consuming queries

SELECT TOP ( 10 )
SUBSTRING(ST.text, ( QS.statement_start_offset / 2 ) + 1,
( ( CASE statement_end_offset
WHEN -1 THEN DATALENGTH(st.text)
ELSE QS.statement_end_offset
END - QS.statement_start_offset ) / 2 ) + 1)
AS statement_text ,execution_count ,
total_worker_time / 1000 AS total_worker_time_ms ,
( total_worker_time / 1000 ) / execution_count
AS avg_worker_time_ms ,
total_logical_reads ,
total_logical_reads / execution_count AS avg_logical_reads ,
total_elapsed_time / 1000 AS total_elapsed_time_ms ,
( total_elapsed_time / 1000 ) / execution_count
AS avg_elapsed_time_ms ,
qp.query_plan
FROM sys.dm_exec_query_stats qs
CROSS APPLY sys.dm_exec_sql_text(qs.sql_handle) st
CROSS APPLY sys.dm_exec_query_plan(qs.plan_handle) qp
ORDER BY total_worker_time DESC
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版权声明：本文为CSDN博主「Burgess_Liu」的原创文章，遵循 CC 4.0 BY-SA 版权协议，转载请附上原文出处链接及本声明。
原文链接：https://blog.csdn.net/Burgess_Liu/article/details/52813727