SQL Update非常慢(大约20-50秒),Select只需不到1秒

Question

我有一个SQL Tabe"文档",其中包含很多行(最多几百万).

当我执行Select-Statement时,大约需要0.5秒.但是当我使用完全相同的WHERE子句执行更新时,大约需要20到50秒,具体取决于受影响的行数.

这是我的声明.

//选择

SELECT * FROM Document 
WHERE (State=20 OR State=23) AND 
LetterClosed IS NOT NULL AND 
TYPE=0 AND
SendLetter=1

//更新

UPDATE Document set State=32 
WHERE (State=20 OR State=23) AND 
LetterClosed IS NOT NULL AND 
TYPE=0 AND
SendLetter=1

OR-Mapper在内部将此update-statement发送到数据库:

exec sp_executesql N'Update
Document
SET
    State=@p4
WHERE
(
  (
    (
      (Document.State = @p0 OR Document.State = @p1) 
      AND Document.LetterClosed IS NOT NULL
    ) 
    AND Document.Type = @p2
  ) 
  AND Document.SendLetter = @p3
)'
,N'@p0 int,@p1 int,@p2 int,@p3 bit,@p4 int',@p0=20,@p1=23,@p2=0,@p3=1,@p4=32

问题是,我在LightSpeed(c#中的数据库OR-Mapper)30秒后得到Timeout-Exception.

谁能在这帮助我？

编辑:

这是我们由SQL-Server自动创建的索引:

CREATE NONCLUSTERED INDEX [_dta_index_Document_9_133575514__K42_1_2_3_4_5_6_7_8_9_11_12_13_14_15_16_17_18_19_20_21_22_23_24_25_26_27_28_29_30_31_32_33_34_] ON [Document] 

(
    [State] ASC
)
INCLUDE ( 
[Id],[DocumentId],[SendLetter],[SendFax],[Archive],[Crm],[Validation],[CreationDate],[PageCount],
[InformationLetter],[TermsOfDelivery],[DeliveryTypeNo],[SeparateDelivery],[FormName],[FormDescription],[TemplateFileName],[RecipientType],
[HealthInsuranceNo],[FamilyHealthInsuranceNo],[PensionInsuranceNo],[EmployerCompanyNo],[RecipientName1],[RecipientName2],[RecipientName3],
[RecipientStreet],[RecipientCountryCode],[RecipientZipCode],[RecipientCity],[RecipientFaxNo],[AuthorId],
[AuthorName],[AuthorEmailAddress],[CostcenterDepartment],[CostcenterDescription],[MandatorNo],[MandatorName],[ControllerId],
[ControllerName],[EditorId],[EditorName],[StateFax],[Editable],[LetterClosedDate],[JobId],[DeliveryId],[DocumentIdExternal],[JobGroupIdExternal],
[GcosyInformed]) WITH (SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, DROP_EXISTING = OFF, ONLINE = OFF) ON [PRIMARY]
go

CREATE NONCLUSTERED INDEX [_dta_index_Document_9_133575514__K2_1_46] ON [Document] 
(
    [DocumentId] ASC
)
INCLUDE ( [Id],
[JobId]) WITH (SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, DROP_EXISTING = OFF, ONLINE = OFF) ON [PRIMARY]
go

CREATE NONCLUSTERED INDEX [_dta_index_Document_9_133575514__K46_K2] ON [Document] 
(
    [JobId] ASC,
    [DocumentId] ASC
)WITH (SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, DROP_EXISTING = OFF, ONLINE = OFF) ON [PRIMARY]
go



CREATE NONCLUSTERED INDEX [Document_State_Id] ON [Document] 
(
    [State] ASC,
    [Id] ASC
)WITH (SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, DROP_EXISTING = OFF, ONLINE = OFF) ON [PRIMARY]
go

CREATE NONCLUSTERED INDEX [Document_State_CreationDate] ON [Document] 
(
    [State] ASC,
    [CreationDate] ASC
)WITH (SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, DROP_EXISTING = OFF, ONLINE = OFF) ON [PRIMARY]
go

编辑2:现在我有一个图形执行计划:执行计划:https://skydrive.live.com/redir？resid = 597F6CF1AB696567!444&authkey =!ABq72SAWXOoAXfI

执行计划索引更新详细信息:https://skydrive.live.com/？cid = 597f6cf1ab696567&id = 597F6CF1AB696567%21445&sff = 1&authkey =!ADDPWvxB2JLLvWo

此SQL-Update大约需要35秒才能执行.通常此更新仅需0.3秒.似乎另一个进程阻止了这个.我看到了一些其他选择,它们在此更新过程中开始,一直等到更新完成,直到完成select-execution.

所以看起来索引本身是正确的(通常是0.3秒执行).所有选择(来自java/jtds,php,.net)都是隔离级别读取提交(默认).这会帮助我在这里更改所有选择读取未提交以避免在索引更新期间阻止此操作吗？

谢谢托比

Answer 1

也许您在表 Document 上有索引。索引使选择速度更快，但更新/插入/删除操作速度较慢。

尝试删除不必要的索引。