那些遇到过的问题

运行 dm_exec_query_stats 性能不佳

Dia*_*ane 5 performance sql-server dmv query-performance

我有一项工作每 5 分钟执行一次，从 DMV 收集两年多没有变化的信息，通常运行时间不到一分钟。

突然从上周开始，在没有部署任何更改的情况下，该作业开始在 15 台服务器中仅 1 台上运行超过 12 分钟。查看执行计划，没有任何变化，但读取、写入、CPU 时间和行计数都变了提高了一个数量级。插入的行数也没有太大变化。

这可能是底层系统表中的错误统计信息吗？如果是这样，如何解决这个问题，因为我无法在任何 DMV 上运行 UPDATE STATISTICS，而 DMV 只提供有关对象不存在的消息。

这是有问题的代码：

SELECT
    ISNULL(DB_NAME(st.dbid), 'NULL') AS [DatabaseName]  
    ,ISNULL(OBJECT_SCHEMA_NAME(st.objectid, st.dbid), 'NULL') AS [SchemaName] 
    ,ISNULL(OBJECT_NAME(st.objectid, st.dbid), 'NULL') AS [ObjectName]   
    ,cp.objtype AS [ObjectType]
    ,qs.statement_start_offset AS [StatementStartOffset]
    ,qs.statement_end_offset AS [StatementEndOffset]
    ,qs.query_hash AS [QueryHash]
    ,qs.query_plan_hash AS [QueryPlanHash]
    ,qs.sql_handle AS [SQLHandle]
    ,qs.plan_handle AS [PlanHandle]
    ,qs.plan_generation_num AS [PlanGenerationNumber]
    ,cp.usecounts AS [UseCounts]
    ,cp.refcounts AS [RefCounts]
    -- find the offset of the actual statement being executed
    ,SUBSTRING(st.text, 
            CASE
                WHEN qs.statement_start_offset = 0 OR qs.statement_start_offset IS NULL THEN 1  
                ELSE qs.statement_start_offset/2 + 1
            END, 
            CASE 
                WHEN qs.statement_end_offset = 0 OR qs.statement_end_offset = -1 OR qs.statement_end_offset IS NULL THEN LEN(st.text)  
                ELSE qs.statement_end_offset/2 
            END - 
            CASE
                WHEN qs.statement_start_offset = 0 OR qs.statement_start_offset IS NULL THEN 1  
                ELSE qs.statement_start_offset/2
            END + 1 
        ) AS [Statement]  
    ,qs.last_execution_time AS [LastExecutionTime]
    ,qs.creation_time AS [CreationTime]
    ,qs.execution_count AS [ExecutionCount]
    ,qs.total_logical_reads AS [TotalLogicalReads]
    ,qs.last_logical_reads AS [LastLogicalReads]
    ,qs.min_logical_reads AS [MinLogicalReads]
    ,qs.max_logical_reads AS [MaxLogicalReads]
    ,qs.total_logical_writes AS [TotalLogicalWrites]
    ,qs.last_logical_writes AS [LastLogicalWrites]
    ,qs.min_logical_writes AS [MinLogicalWrites]
    ,qs.max_logical_writes AS [MaxLogicalWrites]
    ,qs.total_physical_reads AS [TotalPhysicalReads]
    ,qs.last_physical_reads AS [LastPhysicalReads]
    ,qs.min_physical_reads AS [MinPhysicalReads]
    ,qs.max_physical_reads AS [MaxPhysicalReads]
    ,qs.total_worker_time AS [TotalWorkerTime]
    ,qs.last_worker_time AS [LastWorkerTime]
    ,qs.min_worker_time AS [MinWorkerTime]
    ,qs.max_worker_time AS [MaxWorkerTime]
    ,qs.total_clr_time AS [TotalCLRTime]
    ,qs.last_clr_time AS [LastCLRTime]
    ,qs.min_clr_time AS [MinCLRTime]
    ,qs.max_clr_time AS [MaxCLRTime]
    ,qs.total_elapsed_time AS [TotalElapsedTime]
    ,qs.last_elapsed_time AS [LastElapsedTime]
    ,qs.min_elapsed_time AS [MinElapsedTime]
    ,qs.max_elapsed_time AS [MaxElapsedTime]
    ,qs.total_rows AS [TotalRows]
    ,qs.last_rows AS [LastRows]
    ,qs.min_rows AS [MinRows]
    ,qs.max_rows AS [MaxRows]
INTO #QueryUsageStats
FROM sys.dm_exec_query_stats qs   
INNER JOIN sys.dm_exec_cached_plans cp 
ON qs.plan_handle = cp.plan_handle 
CROSS APPLY sys.dm_exec_sql_text(qs.plan_handle) st
WHERE 1=2;

CREATE UNIQUE CLUSTERED INDEX #PK_#QueryUsageStats ON #QueryUsageStats
(
    [DatabaseName] ASC,
    [SchemaName] ASC,
    [ObjectName] ASC,
    [ObjectType] ASC,
    [StatementStartOffset] ASC,
    [StatementEndOffset] ASC,
    [QueryHash] ASC,
    [QueryPlanHash] ASC,
    [PlanHandle] ASC
);

INSERT INTO #QueryUsageStats
SELECT
    ISNULL(DB_NAME(st.dbid), 'NULL') AS [DatabaseName]  
    ,ISNULL(OBJECT_SCHEMA_NAME(st.objectid, st.dbid), 'NULL') AS [SchemaName] 
    ,ISNULL(OBJECT_NAME(st.objectid, st.dbid), 'NULL') AS [ObjectName]   
    ,cp.objtype AS [ObjectType]
    ,qs.statement_start_offset AS [StatementStartOffset]
    ,qs.statement_end_offset AS [StatementEndOffset]
    ,qs.query_hash AS [QueryHash]
    ,qs.query_plan_hash AS [QueryPlanHash]
    ,qs.sql_handle AS [SQLHandle]
    ,qs.plan_handle AS [PlanHandle]
    ,qs.plan_generation_num AS [PlanGenerationNumber]
    ,cp.usecounts AS [UseCounts]
    ,cp.refcounts AS [RefCounts]
    -- find the offset of the actual statement being executed
    ,SUBSTRING(st.text, 
            CASE
                WHEN qs.statement_start_offset = 0 OR qs.statement_start_offset IS NULL THEN 1  
                ELSE qs.statement_start_offset/2 + 1
            END, 
            CASE 
                WHEN qs.statement_end_offset = 0 OR qs.statement_end_offset = -1 OR qs.statement_end_offset IS NULL THEN LEN(st.text)  
                ELSE qs.statement_end_offset/2 
            END - 
            CASE
                WHEN qs.statement_start_offset = 0 OR qs.statement_start_offset IS NULL THEN 1  
                ELSE qs.statement_start_offset/2
            END + 1 
        ) AS [Statement]  
    ,qs.last_execution_time AS [LastExecutionTime]
    ,qs.creation_time AS [CreationTime]
    ,qs.execution_count AS [ExecutionCount]
    ,qs.total_logical_reads AS [TotalLogicalReads]
    ,qs.last_logical_reads AS [LastLogicalReads]
    ,qs.min_logical_reads AS [MinLogicalReads]
    ,qs.max_logical_reads AS [MaxLogicalReads]
    ,qs.total_logical_writes AS [TotalLogicalWrites]
    ,qs.last_logical_writes AS [LastLogicalWrites]
    ,qs.min_logical_writes AS [MinLogicalWrites]
    ,qs.max_logical_writes AS [MaxLogicalWrites]
    ,qs.total_physical_reads AS [TotalPhysicalReads]
    ,qs.last_physical_reads AS [LastPhysicalReads]
    ,qs.min_physical_reads AS [MinPhysicalReads]
    ,qs.max_physical_reads AS [MaxPhysicalReads]
    ,qs.total_worker_time AS [TotalWorkerTime]
    ,qs.last_worker_time AS [LastWorkerTime]
    ,qs.min_worker_time AS [MinWorkerTime]
    ,qs.max_worker_time AS [MaxWorkerTime]
    ,qs.total_clr_time AS [TotalCLRTime]
    ,qs.last_clr_time AS [LastCLRTime]
    ,qs.min_clr_time AS [MinCLRTime]
    ,qs.max_clr_time AS [MaxCLRTime]
    ,qs.total_elapsed_time AS [TotalElapsedTime]
    ,qs.last_elapsed_time AS [LastElapsedTime]
    ,qs.min_elapsed_time AS [MinElapsedTime]
    ,qs.max_elapsed_time AS [MaxElapsedTime]
    ,qs.total_rows AS [TotalRows]
    ,qs.last_rows AS [LastRows]
    ,qs.min_rows AS [MinRows]
    ,qs.max_rows AS [MaxRows]
FROM sys.dm_exec_query_stats qs   
INNER JOIN sys.dm_exec_cached_plans cp 
ON qs.plan_handle = cp.plan_handle 
CROSS APPLY sys.dm_exec_sql_text(qs.plan_handle) st;
Run Code Online (Sandbox Code Playgroud)

这是生成的执行计划：

在此输入图像描述

请注意，我还删除了聚集索引，并且还像选择丢弃查询结果一样运行查询，但仍然需要超过 3 分钟或更多分钟。事实上，即使现在没有加入其他表，甚至没有 order by 子句，仅从 sys.dm_exec_query_stats 选择数据似乎也需要 3 分钟以上。

Bre*_*zar 4

Nick Craver 在 Opserver 中也遇到了性能问题。这是他直接与 MS 人员一起制定查询计划后最终得到的查询 - 连接看起来有点扭曲，但我记得，这是他能够获得一致的良好性能并避免超时问题的唯一方法：

SELECT AvgCPU, AvgDuration, AvgReads, AvgCPUPerMinute,
       TotalCPU, TotalDuration, TotalReads,
       PercentCPU, PercentDuration, PercentReads, PercentExecutions,
       ExecutionCount,
       ExecutionsPerMinute,
       PlanCreationTime, LastExecutionTime,
       SUBSTRING(st.text,
                 (StatementStartOffset / 2) + 1,
                 ((CASE StatementEndOffset
                   WHEN -1 THEN DATALENGTH(st.text)
                   ELSE StatementEndOffset
                   END - StatementStartOffset) / 2) + 1) AS QueryText,
        st.Text FullText,
        query_plan AS QueryPlan,
        PlanHandle,
        StatementStartOffset,
        StatementEndOffset,
        MinReturnedRows,
        MaxReturnedRows,
        AvgReturnedRows,
        TotalReturnedRows,
        LastReturnedRows,
        DB_NAME(DatabaseId) AS CompiledOnDatabase
FROM (SELECT TOP (@MaxResultCount) 
             total_worker_time / execution_count AS AvgCPU,
             total_elapsed_time / execution_count AS AvgDuration,
             total_logical_reads / execution_count AS AvgReads,
             Cast(total_worker_time / age_minutes As BigInt) AS AvgCPUPerMinute,
             execution_count / age_minutes AS ExecutionsPerMinute,
             Cast(total_worker_time / age_minutes_lifetime As BigInt) AS AvgCPUPerMinuteLifetime,
             execution_count / age_minutes_lifetime AS ExecutionsPerMinuteLifetime,
             total_worker_time AS TotalCPU,
             total_elapsed_time AS TotalDuration,
             total_logical_reads AS TotalReads,
             execution_count ExecutionCount,
             CAST(ROUND(100.00 * total_worker_time / t.TotalWorker, 2) AS MONEY) AS PercentCPU,
             CAST(ROUND(100.00 * total_elapsed_time / t.TotalElapsed, 2) AS MONEY) AS PercentDuration,
             CAST(ROUND(100.00 * total_logical_reads / t.TotalReads, 2) AS MONEY) AS PercentReads,
             CAST(ROUND(100.00 * execution_count / t.TotalExecs, 2) AS MONEY) AS PercentExecutions,
             qs.creation_time AS PlanCreationTime,
             qs.last_execution_time AS LastExecutionTime,
             qs.plan_handle AS PlanHandle,
             qs.statement_start_offset AS StatementStartOffset,
             qs.statement_end_offset AS StatementEndOffset,
             qs.min_rows AS MinReturnedRows,
             qs.max_rows AS MaxReturnedRows,
             CAST(qs.total_rows as MONEY) / execution_count AS AvgReturnedRows,
             qs.total_rows AS TotalReturnedRows,
             qs.last_rows AS LastReturnedRows,
             qs.sql_handle AS SqlHandle,
             Cast(pa.value as Int) DatabaseId
        FROM (SELECT *, 
                     CAST((CASE WHEN DATEDIFF(second, creation_time, GETDATE()) > 0 And execution_count > 1
                                THEN DATEDIFF(second, creation_time, GETDATE()) / 60.0
                                ELSE Null END) as MONEY) as age_minutes, 
                     CAST((CASE WHEN DATEDIFF(second, creation_time, last_execution_time) > 0 And execution_count > 1
                                THEN DATEDIFF(second, creation_time, last_execution_time) / 60.0
                                ELSE Null END) as MONEY) as age_minutes_lifetime
                FROM sys.dm_exec_query_stats) AS qs
             CROSS JOIN(SELECT SUM(execution_count) TotalExecs,
                               SUM(total_elapsed_time) TotalElapsed,
                               SUM(total_worker_time) TotalWorker,
                               SUM(total_logical_reads) TotalReads
                          FROM sys.dm_exec_query_stats) AS t
             CROSS APPLY sys.dm_exec_plan_attributes(qs.plan_handle) AS pa
     WHERE pa.attribute = 'dbid'
       {0}) sq
    CROSS APPLY sys.dm_exec_sql_text(SqlHandle) AS st
    CROSS APPLY sys.dm_exec_query_plan(PlanHandle) AS qp
Run Code Online (Sandbox Code Playgroud)

归档时间：

查看次数：

1193 次

最近记录：

7 年，5 月 前
相关归档
如何允许执行存储过程但不允许写入？ 11
在任何 RESTORE DATABASE 事件后自动执行存储过程 9
由于 LSN 链中断，无法创建恢复计划 7
是否可以从 sql server 日志文件中恢复一天的查询？ 6
在 SQL Server 中查询差异变化图 6
SQL Server 无通配符 LIKE 优化 5
每个数据库为 SQL Server 2008 R2 存储了哪些文件的信息在哪里 5
子选择需要“年龄” - EXCEPT要快得多 5
浏览时 SSAS 层次结构重复 1
T-SQL 或 PowerShell 将超过 2 天的 bak 文件移动到另一个位置 0
难疑归档
SQL Server Management Studio 18 无法打开（仅弹出启动画面） 110
重新索引会更新统计信息吗？ 48
什么时候是使用 MariaDB 而不是 MySQL 的合适时机，为什么？ 38
计算每个 MySQL 数据库的磁盘空间使用情况 38
带问号的蓝色图标 - 是什么意思？ 35
IntelliSense 不工作，但已启用 32
使用 SQL CLR 标量函数模拟 HASHBYTES 的可扩展方式是什么？ 31
是否有“最佳实践”类型的过程供开发人员遵循以进行数据库更改？ 31
在 SQL Server 中，当对只有聚集索引的表强制执行索引查找时，我能否保证没有显式 ORDER BY 子句的顺序？ 27
是否有 DBMS 允许引用视图（而不仅仅是基表）的外键？ 23