Requests中出现大量ASYNC_NETWORK_IO等待

七夕活动，网页显示异常：
504 Gateway Time-out The server didn't respond in time.
开发询问数据库是否正常，当时正连接在实例上查询数据，感觉响应确实慢(敲一个命令，要几秒才显示出来)。只分配一个SQL Server身份验证的登录名
1、查看ERRORLOG是否有异常信息

xp_readerrorlog 0,1,null,null,'20170828','20170829','desc'

2、查看连接信息，是否有阻塞、等待类型、连接状态

select spid,kpid,blocked,waittime,waittype,waitresource,dbid,last_batch,status,open_tran 
from sys.sysprocesses where spid>50

在第2步中发现很多waittime>0的连接，且其等待类型全部是ASYNC_NETWORK_IO
3、查看正在执行的语句

SELECT er.session_id
    ,DB_NAME(sp.dbid) [Database]
    ,er.start_time
    ,er.status
    ,er.wait_type
    ,er.wait_time
    ,er.command
    ,er.transaction_isolation_level
    ,er.total_elapsed_time/1000 [total_elapsed_time(s)]
    ,er.estimated_completion_time/1000 [estimated_completion_time(s)]
    ,er.percent_complete
    ,[SQLQuery] = SUBSTRING(qt.Text, (er.statement_start_offset / 2) + 1, ((
            CASE
                WHEN er.statement_end_offset = - 1
                    THEN LEN(CONVERT(NVARCHAR(MAX), qt.TEXT)) * 2
                ELSE er.statement_end_offset
                END - er.statement_start_offset
            ) / 2) + 1)
    ,[BatchQuery] = qt.Text
    ,Program = program_name 
    ,sp.Hostname
    ,sp.loginame
    ,sp.nt_username
    ,sp.nt_domain
FROM sys.dm_exec_requests er
INNER JOIN sys.sysprocesses sp ON er.session_id = sp.spid
CROSS APPLY sys.dm_exec_sql_text(er.sql_handle) AS qt
WHERE er.session_id > 50

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