SQL性能調(diào)優(yōu)
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SQL Server在運(yùn)行一段時(shí)間，隨著數(shù)據(jù)的積累，SQL運(yùn)行效率會(huì)逐步降低，為了使用業(yè)務(wù)系統(tǒng)正常動(dòng)作，經(jīng)常IT部門需要花高價(jià)請(qǐng)SQL調(diào)優(yōu)專家來解決。其實(shí)調(diào)優(yōu)也不復(fù)雜，主要是找到影響效率的SQL，然后對(duì)癥下藥，這里給出幾個(gè)技巧，相信對(duì)大家非常實(shí)用。
1、檢查SQL阻塞原因 select blocking_session_id, wait_duration_ms, session_id
from sys.dm_os_waiting_tasks
where blocking_session_id is not null
2、檢查前10個(gè)等待資源的SQL語句 select top 10 *
from sys.dm_os_wait_stats
order by wait_time_ms desc
3、查詢顯示 CPU 平均占用率最高的前50個(gè)SQL 語句 SELECT TOP 50 total_worker_time/execution_count AS [Avg CPU Time],
(SELECT SUBSTRING(text,statement_start_offset/2,(CASE WHEN statement_end_offset = -1 then LEN(CONVERT(nvarchar(max), text)) * 2 ELSE statement_end_offset end -statement_start_offset)/2) FROM sys.dm_exec_sql_text(sql_handle)) AS query_text, *
FROM sys.dm_exec_query_stats
ORDER BY [Avg CPU Time] DESC
4、CPU 瓶頸通常由以下原因引起：查詢計(jì)劃并非最優(yōu)、配置不當(dāng)、設(shè)計(jì)因素不良或硬件資源不足。下面的常用查詢可幫助您確定導(dǎo)致CPU瓶頸的原因。下面的查詢使您能夠深入了解當(dāng)前緩存的哪些批處理或過程占用了大部分CPU資源。軟件開發(fā)易勢(shì)科技 SELECT TOP 50
SUM(qs.total_worker_time) AS total_cpu_time,
SUM(qs.execution_count) AS total_execution_count,
COUNT(*) AS number_of_statements,
qs.sql_handle
FROM sys.dm_exec_query_stats AS qs
GROUP BY qs.sql_handle
ORDER BY SUM(qs.total_worker_time) DESC
5、下面的查詢顯示緩存計(jì)劃所占用的CPU總使用率（帶 SQL 文本）。 SELECT
total_cpu_time,
total_execution_count,
number_of_statements,
s2.text
ROM
(SELECT TOP 50
SUM(qs.total_worker_time) AS total_cpu_time,
SUM(qs.execution_count) AS total_execution_count,
COUNT(*) AS number_of_statements,
qs.sql_handle
FROM
sys.dm_exec_query_stats AS qs
GROUP BY qs.sql_handle
ORDER BY SUM(qs.total_worker_time) DESC) AS stats
CROSS APPLY sys.dm_exec_sql_text(stats.sql_handle) AS s2
6、下面的示例查詢顯示已重新編譯的前 25 個(gè)存儲(chǔ)過程。plan_generation_num 指示該查詢已重新編譯的次數(shù)。 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
7、效率較低的查詢計(jì)劃可能增大 CPU 占用率。下面的查詢顯示哪個(gè)查詢占用了最多的 CPU 累計(jì)使用率。 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
8、下面的查詢顯示一些可能占用大量 CPU 使用率的運(yùn)算符（例如 ‘%Hash Match%’、‘%Sort%’）以找出可疑對(duì)象。 select *
from
sys.dm_exec_cached_plans
cross apply sys.dm_exec_query_plan(plan_handle)
where
cast(query_plan as nvarchar(max)) like '%Sort%'
or cast(query_plan as nvarchar(max)) like '%Hash Match%'
復(fù)制代碼9、如果已檢測(cè)到效率低下并導(dǎo)致 CPU 占用率較高的查詢計(jì)劃，請(qǐng)對(duì)該查詢中涉及的表運(yùn)行 UPDATE STATISTICS 以查看該問題是否仍然存在。然后，收集相關(guān)數(shù)據(jù)并將此問題報(bào)告給 PerformancePoint Planning 支持人員。如果您的系統(tǒng)存在過多的編譯和重新編譯，可能會(huì)導(dǎo)致系統(tǒng)出現(xiàn)與 CPU 相關(guān)的性能問題。您可以運(yùn)行下面的 DMV 查詢來找出過多的編譯/重新編譯。 select * from sys.dm_exec_query_optimizer_info
where counter = 'optimizations' or counter = 'elapsed time'