带有 FAST_FORWARD 游标循环的存储过程开始快，结束慢

Question

我有一个存储过程，它使用 FAST_FORWARD 游标按时间顺序循环一组约 300k 记录，并根据许多运行变量和标志的状态将它们分配给声明集，部分实现为表变量。我已经对如何基于集合进行了很多思考，但我就是做不到。所以我坚持使用游标方法，需要优化这段代码。

我注意到，前 10% 的进度加载和处理速度非常快（2000 行/秒），接近 20% 的进度已减慢到约 300 行/秒，最后减慢到大约 60 行/秒。

IMO 这可能是由于 4 个原因：

• 光标变慢了，我认为使用 FAST_FORWARD 光标不太可能
• 处理速度变慢。对于我的“组”，我使用插入、更新和删除的表变量。在任何给定时刻都有最大值。这些变量中大约有 10 行。
• 插入目标表的速度变慢。我不明白为什么会这样，我没有在它们上定义触发器，它们只是普通的表。
• 邪恶的魔法

那个或者我的百分比计数器坏了：

SET @curprogress = @curprogress + 1
IF (@curprogress - ((@totprogress / 100) * (FLOOR(@curprogress * 100 / @totprogress)))) BETWEEN 0 AND 1 BEGIN
    SET @msg = CAST(FLOOR(@curprogress * 100 / @totprogress) AS VARCHAR)
    RAISERROR('%s%s', 0, 1, @msg, '%...') WITH NOWAIT;
END

有没有人知道要查找什么以及如何继续加快此查询的速度？

我的代码的符号摘录：

WHILE....
-- Fetch new record to be assigned to one of the open declaration sets
FETCH NEXT INTO @row_field1, @row_field2....
IF (@flag2 = 1) AND ((@flag1 = 0) OR (@row_field1 <> @prevrow_field1)) 
BEGIN
    -- Logging info: we are closing a child declaration set
    INSERT INTO @logtable SELECT '--> LOG MESSAGE'
    INSERT INTO @logtable
    SELECT format_message(@row_field1, @calc_field2, field3...)
    FROM @runningtable_sub S LEFT JOIN @runningtable_main M ON S.MainID = M.ID

    -- Update enddate of parent
    UPDATE M SET M.enddate = DATEADD(day,365,S.enddate)
    FROM @runningtable_sub S
    LEFT JOIN @runningtable_main M
    ON S.MainID = M.ID

    -- close and save child
    INSERT INTO outputtable_main
    SELECT @field1, COALESCE(Z.Field1,'NULL'), S.startdate, S.enddate,
        M.Startdate, M.Enddate
    FROM @runningtable_sub S 
    LEFT JOIN @runningtable_main M ON S.MainID = M.ID

    -- delete child from running table
    DELETE FROM @runningtable_sub WHERE S.enddate < @curdate
END

Answer 1

我可以想到很多原因会变慢，但如果不知道数据的基数就很难缩小范围。

随机观察：

1. 你的 format_message() 函数肯定是狗；所有 UDF 都是。但是您每次要插入多少行？
2. @runningtable_main 永远不会被清除。
3. 更新成本很高
4. 删除成本很高。如果您使用临时表并修改您的实现，您可以截断而不是删除

要自己解决一些问题，请添加工具：

DECLARE @now DATETIME, @duration INT, @rowcount INT

WHILE....
-- Fetch new record to be assigned to one of the open declaration sets
FETCH NEXT INTO @row_field1, @row_field2....
IF (@flag2 = 1) AND ((@flag1 = 0) OR (@row_field1 <> @prevrow_field1)) 
BEGIN
    PRINT '---------------'

    -- Logging info: we are closing a child declaration set
    INSERT INTO @logtable SELECT '--> LOG MESSAGE'
    SET @now = GETDATE()
    INSERT INTO @logtable
    SELECT format_message(@row_field1, @calc_field2, field3...)
    FROM @runningtable_sub S LEFT JOIN @runningtable_main M ON S.MainID = M.ID
    SELECT @rowcount = @@ROWCOUNT, @duration = DATEDIFF(ms,@now,GETDATE)
    RAISERROR('%i row(s) inserted into @logtable, %i milliseconds',-1,-1,@rowcount,@duration) WITH NOWAIT

    -- Update enddate of parent
    SET @now = GETDATE()
    UPDATE M SET M.enddate = DATEADD(day,365,S.enddate)
    FROM @runningtable_sub S
    LEFT JOIN @runningtable_main M
    ON S.MainID = M.ID
    SELECT @rowcount = @@ROWCOUNT, @duration = DATEDIFF(ms,@now,GETDATE)
    RAISERROR('%i row(s) updated in @runningtable_main, %i milliseconds',-1,-1,@rowcount,@duration) WITH NOWAIT

    -- close and save child
    SET @now = GETDATE()
    INSERT INTO outputtable_main
    SELECT @field1, COALESCE(Z.Field1,'NULL'), S.startdate, S.enddate,
        M.Startdate, M.Enddate
    FROM @runningtable_sub S 
    LEFT JOIN @runningtable_main M ON S.MainID = M.ID
    SELECT @rowcount = @@ROWCOUNT, @duration = DATEDIFF(ms,@now,GETDATE)
    RAISERROR('%i row(s) inserted into outputtable_main, %i milliseconds',-1,-1,@rowcount,@duration) WITH NOWAIT

    -- delete child from running table
    SET @now = GETDATE()
    DELETE FROM @runningtable_sub WHERE S.enddate < @curdate
    SELECT @rowcount = @@ROWCOUNT, @duration = DATEDIFF(ms,@now,GETDATE)
    RAISERROR('%i row(s) deleted from @runningtable_sub, %i milliseconds',-1,-1,@rowcount,@duration) WITH NOWAIT
END

如果您包含了整个代码（包括游标声明），而不仅仅是一个符号摘录，这里的某个人可能会为您重新编写它以提高效率和/或一起避免使用游标。