URGENT - Problem with read commited isolation level

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URGENT - Problem with read commited isolation level

spaliwal

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Points: 544
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January 13, 2004 at 4:21 am

#106728

Hi Gurus,

I am using default READ COMMITED isolation level . While inserting a single

row in a table it is now allowing to read any row from the table. As i know

it uses row level locking then why it is now allowing to read rows which are

already commited ?

say table name ABC with code, Name coloumns

existing rows are -

01 Tom

02 Jerry

03 Mouse

Say in a session i am giving and it is not commited yet

INSERT INO ABC values ('04','Mickey')

and in another session Immediately i give

SELECT * from ABC where Code = '01'

It wont return any row for 01 even it is already commited

locks on the table are

RID X

Page IX

Table IX

Database S

Immediate help is greatly appreciated .

TIA ,

Sheilesh

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Johan Bijnens SSC Guru Points: 134873 More actions · Answer 1

Do you have an index on column Code ?

If not it will have to perform a table-scan and therefor it will not be able to read through the uncommitted row(s).

Johan

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spaliwal Mr or Mrs. 500 Points: 544 More actions · Answer 2

Oops , My question is wrong - Pl. read the below one text 'now' is changed to 'not'

Alzdba, I dont have index on 'Code' field

Hi Gurus,

I am using default READ COMMITED isolation level . While inserting a single

row in a table it is not allowing to read any other row from the table. As i know

it uses row level locking then why it is not allowing to read rows which are

already commited ?

say table name ABC with code, Name coloumns

existing rows are -

01 Tom

02 Jerry

03 Mouse

Say in a session i am giving INSERT and it is not commited yet -

INSERT INTO ABC values ('04','Mickey')

and in another session Immediately i give

SELECT * from ABC where Code = '01'

It wont return any row for 01 even 01 row is already commited.

locks on the table are

RID X

Page IX

Table IX

Database S

Immediate help is greatly appreciated .

TIA ,

Sheilesh

Johan Bijnens SSC Guru Points: 134873 More actions · Answer 3

read my previous reply

Activate the "show (estimated) execution plan" in QueryAnalyser, maybe that will clarify the issue.

Johan

Learn to play, play to learn !

Dont drive faster than your guardian angel can fly ...
but keeping both feet on the ground wont get you anywhere :w00t:

- How to post Performance Problems
- How to post data/code to get the best help[/url]

- How to prevent a sore throat after hours of presenting ppt

press F1 for solution, press shift+F1 for urgent solution 😀

Need a bit of Powershell? How about this

Who am I ? Sometimes this is me but most of the time this is me

spaliwal Mr or Mrs. 500 Points: 544 More actions · Answer 4

spaliwal

Mr or Mrs. 500

Points: 544

January 13, 2004 at 6:55 am

#489730

alzdba,

I am not getting your comments in last mail.Pl. elaborate.where will i should see the execution plan in INSERT session or in SELECT session ?

Johan Bijnens SSC Guru Points: 134873 More actions · Answer 5

Perform it on both, maybe that gets it all into the daylight, but at least perform it where you are having the problem (i.e. the select).

- QA\Query\display estimated execution plan

- QA\Query\show execution plan

Johan

Learn to play, play to learn !

Dont drive faster than your guardian angel can fly ...
but keeping both feet on the ground wont get you anywhere :w00t:

- How to post Performance Problems
- How to post data/code to get the best help[/url]

- How to prevent a sore throat after hours of presenting ppt

press F1 for solution, press shift+F1 for urgent solution 😀

Need a bit of Powershell? How about this

Who am I ? Sometimes this is me but most of the time this is me

justevolved SSC Enthusiast Points: 188 More actions · Answer 6

The Problem lies in how sql server handles locking mechanism. If sql server feels that placing 4 row locks would be more resource intensive than placing a single page lock it would do the latter.

So in u'r case if there is no index on the column which is in the where clause sql server does a table scan and hence does not return u the row. Try and put an index on the column and the row will be returned. As suggested try and check the execution plan.

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