人人都是 DBA（XI）I/O 信息收集脚本汇编

原文:

什么？有个 SQL 执行了 8 秒！

哪里出了问题？臣妾不知道啊，得找 DBA 啊。

DBA 人呢？离职了！！擦！！！

程序员在无处寻求帮助时，就得想办法自救，努力让自己变成 "伪 DBA"。

索引

数据文件和日志文件位置和大小

SELECT DB_NAME([database_id]) AS [Database Name]
    ,[file_id]
    ,[name]
    ,physical_name
    ,type_desc
    ,state_desc
    ,is_percent_growth
    ,growth
    ,CONVERT(BIGINT, growth / 128.0) AS [Growth in MB]
    ,CONVERT(BIGINT, size / 128.0) AS [Total Size in MB]
FROM sys.master_files WITH (NOLOCK)
WHERE [database_id] > 4
    AND [database_id] <> 32767
    OR [database_id] = 2
ORDER BY DB_NAME([database_id])
OPTION (RECOMPILE);

通常会查看：

• 数据文件是否与日志文件放到了不同的磁盘上？
• 难道都装到了 C 盘上？
• tempdb 是否指定了独立的磁盘？
• 有几个 tempdb 文件？
• 这些 tempdb 都多大了？
• 数据库是否包含多个文件？
• 数据文件的增长步长合适吗？

查看指定数据库文件的大小和可用空间

需要指定数据库，或使用 use 指定，例如 use TEST。

SELECT f.[name] AS [File Name]
    ,f.physical_name AS [Physical Name]
    ,CAST((f.size / 128.0) AS DECIMAL(15, 2)) AS [Total Size in MB]
    ,CAST(f.size / 128.0 - CAST(FILEPROPERTY(f.[name], ‘SpaceUsed‘) AS INT) / 128.0 AS DECIMAL(15, 2)) AS [Available Space In MB]
    ,[file_id]
    ,fg.[name] AS [Filegroup Name]
FROM sys.database_files AS f WITH (NOLOCK)
LEFT OUTER JOIN sys.data_spaces AS fg WITH (NOLOCK) ON f.data_space_id = fg.data_space_id
OPTION (RECOMPILE);

服务器 Disk 容量和挂载信息

SELECT DISTINCT vs.volume_mount_point
    ,vs.file_system_type
    ,vs.logical_volume_name
    ,CONVERT(DECIMAL(18, 2), vs.total_bytes / 1073741824.0) AS [Total Size (GB)]
    ,CONVERT(DECIMAL(18, 2), vs.available_bytes / 1073741824.0) AS [Available Size (GB)]
    ,CAST(CAST(vs.available_bytes AS FLOAT) / CAST(vs.total_bytes AS FLOAT) AS DECIMAL(18, 2)) * 100 AS [Space Free %]
FROM sys.master_files AS f WITH (NOLOCK)
CROSS APPLY sys.dm_os_volume_stats(f.database_id, f.[file_id]) AS vs
OPTION (RECOMPILE);

SELECT db_name(vs.database_id) AS DatabaseName
    ,vs.file_id
    ,vs.volume_mount_point
    ,vs.volume_id
    ,vs.logical_volume_name
    ,vs.file_system_type
    ,(vs.total_bytes / 1024 / 1024 / 1024) AS [TotalSize(GB)]
    ,(vs.available_bytes / 1024 / 1024 / 1024) AS [AvailableSize(GB)]
    ,vs.supports_compression
    ,vs.supports_alternate_streams
    ,vs.supports_sparse_files
    ,vs.is_read_only
    ,vs.is_compressed
FROM sys.master_files mf
CROSS APPLY sys.dm_os_volume_stats(mf.database_id, mf.file_id) vs;

查看 Disk 剩余空间

EXEC master.dbo.xp_fixeddrives

SELECT DISTINCT SUBSTRING(volume_mount_point, 1, 1) AS Volume_mount_point
    ,total_bytes / 1024 / 1024 AS Total_MB
    ,available_bytes / 1024 / 1024 AS Available_MB
FROM sys.master_files AS f
CROSS APPLY sys.dm_os_volume_stats(f.database_id, f.file_id);

查询数据库设置的 Recovery Model

SELECT db.[name] AS [Database Name]
    ,db.recovery_model_desc AS [Recovery Model]
    ,db.state_desc
    ,db.log_reuse_wait_desc AS [Log Reuse Wait Description]
    ,CONVERT(DECIMAL(18, 2), ls.cntr_value / 1024.0) AS [Log Size (MB)]
    ,CONVERT(DECIMAL(18, 2), lu.cntr_value / 1024.0) AS [Log Used (MB)]
    ,CAST(CAST(lu.cntr_value AS FLOAT) / CAST(ls.cntr_value AS FLOAT) AS DECIMAL(18, 2)) * 100 AS [Log Used %]
    ,db.[compatibility_level] AS [DB Compatibility Level]
    ,db.page_verify_option_desc AS [Page Verify Option]
    ,db.is_auto_create_stats_on
    ,db.is_auto_update_stats_on
    ,db.is_auto_update_stats_async_on
    ,db.is_parameterization_forced
    ,db.snapshot_isolation_state_desc
    ,db.is_read_committed_snapshot_on
    ,db.is_auto_close_on
    ,db.is_auto_shrink_on
    ,db.target_recovery_time_in_seconds
    ,db.is_cdc_enabled
FROM sys.databases AS db WITH (NOLOCK)
INNER JOIN sys.dm_os_performance_counters AS lu WITH (NOLOCK) ON db.NAME = lu.instance_name
INNER JOIN sys.dm_os_performance_counters AS ls WITH (NOLOCK) ON db.NAME = ls.instance_name
WHERE lu.counter_name LIKE N‘Log File(s) Used Size (KB)%‘
    AND ls.counter_name LIKE N‘Log File(s) Size (KB)%‘
    AND ls.cntr_value > 0
OPTION (RECOMPILE);

通常会关注：

• 数据库实例（Instance）上建立了多少个数据库？
• 它们都分别使用了什么恢复模型（Recovery Model）？
• Log 重用是如何设置的？
• 事务日志（Transaction Log）现在多大了？
• 兼容等级（Compatibility Level）是怎么配置的？
• 页验证选项（Page Verify Option）的设置是什么？通常为 CHECKSUM。
• 是否设置了 Auto Update Statistics Asynchronously 选项？
• 确保未开启 auto_shrink 和 auto_close 选项。

查看最近的 Full Backup 信息

SELECT TOP (30) bs.machine_name
    ,bs.server_name
    ,bs.database_name AS [Database Name]
    ,bs.recovery_model
    ,CONVERT(BIGINT, bs.backup_size / 1048576) AS [Uncompressed Backup Size (MB)]
    ,CONVERT(BIGINT, bs.compressed_backup_size / 1048576) AS [Compressed Backup Size (MB)]
    ,CONVERT(NUMERIC(20, 2), (CONVERT(FLOAT, bs.backup_size) / CONVERT(FLOAT, bs.compressed_backup_size))) AS [Compression Ratio]
    ,DATEDIFF(SECOND, bs.backup_start_date, bs.backup_finish_date) AS [Backup Elapsed Time (sec)]
    ,bs.backup_finish_date AS [Backup Finish Date]
FROM msdb.dbo.backupset AS bs WITH (NOLOCK)
WHERE DATEDIFF(SECOND, bs.backup_start_date, bs.backup_finish_date) > 0
    AND bs.backup_size > 0
    AND bs.type = ‘D‘ -- Change to L if you want Log backups
    AND database_name = DB_NAME(DB_ID())
ORDER BY bs.backup_finish_date DESC
OPTION (RECOMPILE);

获取所有数据库的 VLF 数量

VLF ：Virtual Log File

SQL Server 将日志文件 LDF 划分为多个 VLF 以提高日志处理效率。VLF 的数量和大小不能通过配置指定，SQL Server 会按情况自行判断处理，而如果生成了过多的 VLF 则会产生性能问题。通过指定合理的日志文件初始大小和增长步长，可以有效的防止过多 VLF 的产生。

• 1M-64M 　　4
• 64M-1GB     8
• >1GB          16

CREATE TABLE #VLFInfo (
    RecoveryUnitID INT
    ,FileID INT
    ,FileSize BIGINT
    ,StartOffset BIGINT
    ,FSeqNo BIGINT
    ,[Status] BIGINT
    ,Parity BIGINT
    ,CreateLSN NUMERIC(38)
    );

CREATE TABLE #VLFCountResults (
    DatabaseName SYSNAME
    ,VLFCount INT
    );

EXEC sp_MSforeachdb N‘Use [?]; 

                INSERT INTO #VLFInfo 
                EXEC sp_executesql N‘‘DBCC LOGINFO([?])‘‘; 
     
                INSERT INTO #VLFCountResults 
                SELECT DB_NAME(), COUNT(*) 
                FROM #VLFInfo; 

                TRUNCATE TABLE #VLFInfo;‘

SELECT DatabaseName
    ,VLFCount
FROM #VLFCountResults
ORDER BY VLFCount DESC;

DROP TABLE #VLFInfo;

DROP TABLE #VLFCountResults;

较高的 VLF 数量会影响写入性能，并且会使数据库的恢复过程变慢，通常需要保持 VLF Counts 在 200 以下。

SQL Server 的错误日志位置

SELECT is_enabled
    ,[path]
    ,max_size
    ,max_files
FROM sys.dm_os_server_diagnostics_log_configurations WITH (NOLOCK)
OPTION (RECOMPILE);

查询近期的 Error Log 信息

DECLARE @Time_Start DATETIME;
DECLARE @Time_End DATETIME;

SET @Time_Start = getdate() - 2;
SET @Time_End = getdate();

-- Create the temporary table
CREATE TABLE #ErrorLog (
    logdate DATETIME
    ,processinfo VARCHAR(255)
    ,Message VARCHAR(500)
    )

-- Populate the temporary table
INSERT #ErrorLog (
    logdate
    ,processinfo
    ,Message
    )
EXEC master.dbo.xp_readerrorlog 0
    ,1
    ,NULL
    ,NULL
    ,@Time_Start
    ,@Time_End
    ,N‘desc‘;

-- Filter the temporary table
SELECT LogDate
    ,Message
FROM #ErrorLog
WHERE (
        Message LIKE ‘%error%‘
        OR Message LIKE ‘%failed%‘
        )
    AND processinfo NOT LIKE ‘logon‘
ORDER BY logdate DESC

-- Drop the temporary table 
DROP TABLE #ErrorLog

在错误日志中查询 I/O 超过 15s 的请求

CREATE TABLE #IOWarningResults (
    LogDate DATETIME
    ,ProcessInfo SYSNAME
    ,LogText NVARCHAR(1000)
    );

INSERT INTO #IOWarningResults
EXEC xp_readerrorlog 0
    ,1
    ,N‘taking longer than 15 seconds‘;

INSERT INTO #IOWarningResults
EXEC xp_readerrorlog 1
    ,1
    ,N‘taking longer than 15 seconds‘;

INSERT INTO #IOWarningResults
EXEC xp_readerrorlog 2
    ,1
    ,N‘taking longer than 15 seconds‘;

INSERT INTO #IOWarningResults
EXEC xp_readerrorlog 3
    ,1
    ,N‘taking longer than 15 seconds‘;

INSERT INTO #IOWarningResults
EXEC xp_readerrorlog 4
    ,1
    ,N‘taking longer than 15 seconds‘;

SELECT LogDate
    ,ProcessInfo
    ,LogText
FROM #IOWarningResults
ORDER BY LogDate DESC;

DROP TABLE #IOWarningResults;

如果能够查询出结果，可以说明 I/O 性能存在问题，但是哪里引起的还需进一步探索。

查询 Disk 的性能指标

SELECT [Drive]
    ,CASE 
        WHEN num_of_reads = 0
            THEN 0
        ELSE (io_stall_read_ms / num_of_reads)
        END AS [Read Latency (ms)]
    ,CASE 
        WHEN io_stall_write_ms = 0
            THEN 0
        ELSE (io_stall_write_ms / num_of_writes)
        END AS [Write Latency (ms)]
    ,CASE 
        WHEN (
                num_of_reads = 0
                AND num_of_writes = 0
                )
            THEN 0
        ELSE (io_stall / (num_of_reads + num_of_writes))
        END AS [Overall Latency (ms)]
    ,CASE 
        WHEN num_of_reads = 0
            THEN 0
        ELSE (num_of_bytes_read / num_of_reads)
        END AS [Avg Bytes/Read]
    ,CASE 
        WHEN io_stall_write_ms = 0
            THEN 0
        ELSE (num_of_bytes_written / num_of_writes)
        END AS [Avg Bytes/Write]
    ,CASE 
        WHEN (
                num_of_reads = 0
                AND num_of_writes = 0
                )
            THEN 0
        ELSE ((num_of_bytes_read + num_of_bytes_written) / (num_of_reads + num_of_writes))
        END AS [Avg Bytes/Transfer]
FROM (
    SELECT LEFT(UPPER(mf.physical_name), 2) AS Drive
        ,SUM(num_of_reads) AS num_of_reads
        ,SUM(io_stall_read_ms) AS io_stall_read_ms
        ,SUM(num_of_writes) AS num_of_writes
        ,SUM(io_stall_write_ms) AS io_stall_write_ms
        ,SUM(num_of_bytes_read) AS num_of_bytes_read
        ,SUM(num_of_bytes_written) AS num_of_bytes_written
        ,SUM(io_stall) AS io_stall
    FROM sys.dm_io_virtual_file_stats(NULL, NULL) AS vfs
    INNER JOIN sys.master_files AS mf WITH (NOLOCK) ON vfs.database_id = mf.database_id
        AND vfs.file_id = mf.file_id
    GROUP BY LEFT(UPPER(mf.physical_name), 2)
    ) AS tab
ORDER BY [Overall Latency (ms)]
OPTION (RECOMPILE);

通常 Latency 的值大于 20-25 ms 时可考虑有性能问题。

查看哪个数据库文件 I/O 瓶颈最严重

SELECT DB_NAME(fs.database_id) AS [Database Name]
    ,CAST(fs.io_stall_read_ms / (1.0 + fs.num_of_reads) AS NUMERIC(10, 1)) AS [avg_read_stall_ms]
    ,CAST(fs.io_stall_write_ms / (1.0 + fs.num_of_writes) AS NUMERIC(10, 1)) AS [avg_write_stall_ms]
    ,CAST((fs.io_stall_read_ms + fs.io_stall_write_ms) / (1.0 + fs.num_of_reads + fs.num_of_writes) AS NUMERIC(10, 1)) AS [avg_io_stall_ms]
    ,CONVERT(DECIMAL(18, 2), mf.size / 128.0) AS [File Size (MB)]
    ,mf.physical_name
    ,mf.type_desc
    ,fs.io_stall_read_ms
    ,fs.num_of_reads
    ,fs.io_stall_write_ms
    ,fs.num_of_writes
    ,fs.io_stall_read_ms + fs.io_stall_write_ms AS [io_stalls]
    ,fs.num_of_reads + fs.num_of_writes AS [total_io]
FROM sys.dm_io_virtual_file_stats(NULL, NULL) AS fs
INNER JOIN sys.master_files AS mf WITH (NOLOCK) ON fs.database_id = mf.database_id
    AND fs.[file_id] = mf.[file_id]
ORDER BY avg_io_stall_ms DESC
OPTION (RECOMPILE);

考虑将数据库文件移动到不同的磁盘上，或更快的磁盘阵列上以改进性能。

按照 Write I/O 进行排名

SELECT [ReadLatency] = CASE 
        WHEN [num_of_reads] = 0
            THEN 0
        ELSE ([io_stall_read_ms] / [num_of_reads])
        END
    ,[WriteLatency] = CASE 
        WHEN [num_of_writes] = 0
            THEN 0
        ELSE ([io_stall_write_ms] / [num_of_writes])
        END
    ,[Latency] = CASE 
        WHEN (
                [num_of_reads] = 0
                AND [num_of_writes] = 0
                )
            THEN 0
        ELSE ([io_stall] / ([num_of_reads] + [num_of_writes]))
        END
    ,[AvgBytesPerRead] = CASE 
        WHEN [num_of_reads] = 0
            THEN 0
        ELSE ([num_of_bytes_read] / [num_of_reads])
        END
    ,[AvgBytesPerWrite] = CASE 
        WHEN [num_of_writes] = 0
            THEN 0
        ELSE ([num_of_bytes_written] / [num_of_writes])
        END
    ,[AvgBytesPerTransfer] = CASE 
        WHEN (
                [num_of_reads] = 0
                AND [num_of_writes] = 0
                )
            THEN 0
        ELSE (([num_of_bytes_read] + [num_of_bytes_written]) / ([num_of_reads] + [num_of_writes]))
        END
    ,LEFT([mf].[physical_name], 2) AS [Drive]
    ,DB_NAME([vfs].[database_id]) AS [DB]
    ,[mf].[physical_name]
    ,[mf].file_id
FROM sys.dm_io_virtual_file_stats(NULL, NULL) AS [vfs]
JOIN sys.master_files AS [mf] ON [vfs].[database_id] = [mf].[database_id]
    AND [vfs].[file_id] = [mf].[file_id]
ORDER BY [WriteLatency] DESC;

获取数据库的 I/O 使用率

WITH Aggregate_IO_Statistics
AS (
    SELECT DB_NAME(database_id) AS [Database Name]
        ,CAST(SUM(num_of_bytes_read + num_of_bytes_written) / 1048576 AS DECIMAL(12, 2)) AS io_in_mb
    FROM sys.dm_io_virtual_file_stats(NULL, NULL) AS [DM_IO_STATS]
    GROUP BY database_id
    )
SELECT ROW_NUMBER() OVER (
        ORDER BY io_in_mb DESC
        ) AS [I/O Rank]
    ,[Database Name]
    ,io_in_mb AS [Total I/O (MB)]
    ,CAST(io_in_mb / SUM(io_in_mb) OVER () * 100.0 AS DECIMAL(5, 2)) AS [I/O Percent]
FROM Aggregate_IO_Statistics
ORDER BY [I/O Rank]
OPTION (RECOMPILE);

查看指定数据库文件的 I/O 状况

需要指定数据库，或使用 use 指定，例如 use TEST。

SELECT DB_NAME(DB_ID()) AS [Database Name]
    ,df.[name] AS [Logical Name]
    ,vfs.[file_id]
    ,df.physical_name AS [Physical Name]
    ,vfs.num_of_reads
    ,vfs.num_of_writes
    ,vfs.io_stall_read_ms
    ,vfs.io_stall_write_ms
    ,CAST(100. * vfs.io_stall_read_ms / (vfs.io_stall_read_ms + vfs.io_stall_write_ms) AS DECIMAL(10, 1)) AS [IO Stall Reads Pct]
    ,CAST(100. * vfs.io_stall_write_ms / (vfs.io_stall_write_ms + vfs.io_stall_read_ms) AS DECIMAL(10, 1)) AS [IO Stall Writes Pct]
    ,(vfs.num_of_reads + vfs.num_of_writes) AS [Writes + Reads]
    ,CAST(vfs.num_of_bytes_read / 1048576.0 AS DECIMAL(10, 2)) AS [MB Read]
    ,CAST(vfs.num_of_bytes_written / 1048576.0 AS DECIMAL(10, 2)) AS [MB Written]
    ,CAST(100. * vfs.num_of_reads / (vfs.num_of_reads + vfs.num_of_writes) AS DECIMAL(10, 1)) AS [# Reads Pct]
    ,CAST(100. * vfs.num_of_writes / (vfs.num_of_reads + vfs.num_of_writes) AS DECIMAL(10, 1)) AS [# Write Pct]
    ,CAST(100. * vfs.num_of_bytes_read / (vfs.num_of_bytes_read + vfs.num_of_bytes_written) AS DECIMAL(10, 1)) AS [Read Bytes Pct]
    ,CAST(100. * vfs.num_of_bytes_written / (vfs.num_of_bytes_read + vfs.num_of_bytes_written) AS DECIMAL(10, 1)) AS [Written Bytes Pct]
FROM sys.dm_io_virtual_file_stats(DB_ID(), NULL) AS vfs
INNER JOIN sys.database_files AS df WITH (NOLOCK) ON vfs.[file_id] = df.[file_id]
OPTION (RECOMPILE);

协助从 I/O 角度来观察数据库文件所承载的压力。

找出 I/O 平均使用最多的语句

SELECT TOP (50) OBJECT_NAME(qt.objectid, dbid) AS [SP Name]
    ,(qs.total_logical_reads + qs.total_logical_writes) / qs.execution_count AS [Avg IO]
    ,qs.execution_count AS [Execution Count]
    ,SUBSTRING(qt.[text], qs.statement_start_offset / 2 + 1, (
            CASE 
                WHEN qs.statement_end_offset = - 1
                    THEN LEN(CONVERT(NVARCHAR(max), qt.[text])) * 2
                ELSE qs.statement_end_offset
                END - qs.statement_start_offset
            ) / 2) AS [Query Text]
FROM sys.dm_exec_query_stats AS qs WITH (NOLOCK)
CROSS APPLY sys.dm_exec_sql_text(qs.sql_handle) AS qt
WHERE qt.[dbid] = DB_ID()
ORDER BY [Avg IO] DESC
OPTION (RECOMPILE);

参考资料：

查询正在等待 I/O 的请求等待时间

SELECT DB_NAME(database_id) AS [DBNAME]
    ,file_id
    ,io_stall
    ,io_pending_ms_ticks
    ,scheduler_address
FROM sys.dm_io_virtual_file_stats(NULL, NULL) iovfs
    ,sys.dm_io_pending_io_requests AS iopior
WHERE iovfs.file_handle = iopior.io_handle

《人人都是 DBA》系列文章索引：

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