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      公司LCS开通了对外和MSN通讯的供能,可老板要求员工只能和经过审批的人员通讯。跟踪Sql Server后发现解决之道,现分享给大家。
      先在LCS的数据库 rtc 增加一个Table 如mycontact, 只有一列 UserAtHost ,类型为 nvarchar 450,将公司允许的联络人汇入,然后修改名为
RtcpEnsureResourceExists 的 procedure 。以 下是修改过的,其中红色部分是新增的语句,xxx.com.cn是公司的网域名

---------------------------------------------------------------------------
--
--
CREATE procedure RtcpEnsureResourceExists
    @_UserAtHost    nvarchar(4000),
  
    @_ResourceId    ResourceId output
as
    set nocount on
    declare @Error int
    declare  @_contact          nvarchar(4000)
    --
    -- Check to see if the resource already exists; if not, insert it.
    --
    select @_ResourceId = ResourceId
      from Resource
     where UserAtHost = @_UserAtHost
 
    select @_contact=UserAtHost
     from mycontact
    where UserAtHost = @_UserAtHost
 
    if ((@_ResourceId is null) and (@_contact is not null)) or (@_UserAtHost like '%xxx.com.cn')  begin
        --
        -- Deadlock possibility:
        -- Unfortunately we have the potential for deadlock here.  If two
        -- connections have both acquired the shared lock on the row due
        -- to the query above, and the row does not exist, they both
        -- will try to escalate their shared lock to an exclusive lock in
        -- order to perform the following insert.  Preventing this by
        -- using with (updlock) on the select would not be a good thing
        -- however.  This is because the update lock would be held for the
        -- duration of the transaction (because we run at a high enough
        -- isolation level) thus preventing anyone from even selecting the
        -- row until our transaction was completed.  We explicitly choose
        -- the possibility of deadlock over the reduced concurrency.  Note
        -- that the possibility of deadlock is extremely rare -- two
        -- connections need to be ensuring that the same row exists at
        -- the same time when it doesn't exist.
        --
        insert Resource (UserAtHost) values (@_UserAtHost)
        set @Error = @@error
        if (@Error = 0) begin
            set @_ResourceId = scope_identity()
            return 0
        end
        --
        -- Unique key violation - row already exists, so select it again.
        --
        else if (@Error = 2627) begin
            select @_ResourceId = ResourceId
              from Resource
             where UserAtHost = @_UserAtHost
            if (@_ResourceId is null) begin
                exec dbo.DbRaiseError @@procid, 50120, @_UserAtHost
                return -1
            end
            else begin
                --
                -- Raise an error to indicate that Unique key violation was
                -- handled.
                --
                exec dbo.DbRaiseError @@procid, 50002
                return 0
            end
        end
        --
        -- Some other problem with inserting the row.
        --
        else begin
            exec dbo.DbRaiseError @@procid, 50001
            return -1
        end
    end
GO
posted on 2006-10-13 12:44 Kevensun 阅读(155) 评论(0)  编辑 收藏 引用
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