We have implemented snapshot isolation level in one of our production database in order to avoid blocking at the time of snapshot generation process in replication..I have impletemented on database level used below query

alter database dbname set read_committed_snapshot ON.

Without using allow_snapshot_isolation ON does it work ?

I have a question about followiing scenario:

I have excecuted the following command for session 1:

SET TRANSACTION ISOLATION LEVEL SNAPSHOT
BEGIN TRAN
SELECT entity_updateTime
FROM user_Table
GO

SET TRANSACTION ISOLATION LEVEL SNAPSHOT
BEGIN TRAN
UPDATE User_Table
SET entity_UpdateTime=GETDATE()
GO

Now let us say if i tried to execute the same command for session 2. It seems table is locked. I can not see output. Getting error message “Executing query…..”

SET TRANSACTION ISOLATION LEVEL SNAPSHOT
BEGIN TRAN
SELECT entity_updateTime
FROM user_Table
GO

SET TRANSACTION ISOLATION LEVEL SNAPSHOT
BEGIN TRAN
UPDATE User_Table
SET entity_UpdateTime=GETDATE()
GO

Any help is greatly appreciated !

Best Wishes,
Brij

–UNIT PRICE IS 18 PRIOR TO TRANSACTION
–THOUGHT ROW COPIED TO tempdb UNIT PRICE WOULD BE 18
–WHY DOES IT COPY 19 AND NOT 18 PRIOR TO TRANSACTION START

SET TRANSACTION ISOLATION LEVEL SNAPSHOT;
BEGIN TRAN;
UPDATE production.products SET
unitprice +=1 FROM production.products WHERE productid=1;

SELECT unitprice FROM production.products WHERE productid=1;
COMMIT TRAN;

–UNIT PRICE RESULTS RETURN 19

here we get strange issue with ISOLATION LEVEL SNAPSHOT in one of our sql stored procedure

we have used the ISOLATION LEVEL SNAPSHOT in stored procedure : test1.sql

and from this sp we called the sql function name “testfun.sql” from this sp ,
and as per my knowledge , we can not use any isolation level in sql function.

and the our sql stored procedure “test1.sql” just have select query only, but it give me the below error

and sql function “testfun.sql” have one temp declared table and we just insert data in it and return that table from the function

“com.microsoft.sqlserver.jdbc.SQLServerException:
Snapshot isolation transaction failed in database ‘test’ because
the object accessed by the statement has been modified by a DDL statement
in another concurrent transaction since the start of this transaction.
It is disallowed because the metadata is not versioned.
A concurrent update to metadata can lead to inconsistency if mixed with snapshot isolation.
”

now what is the root caue of the issue, can you help me to resolve my issue?

Thanks

Thank you for this excellent post!

I tried the queries however didn’t get the expected result…

Step 1:
ALTER DATABASE AdventureWorks
SET ALLOW_SNAPSHOT_ISOLATION ON
GO

Step 2:
SELECT ModifiedDate
FROM HumanResources.Shift
GO

Step 3:
– Session 1
SET TRANSACTION ISOLATION LEVEL SNAPSHOT
BEGIN TRAN
UPDATE HumanResources.Shift
SET ModifiedDate = GETDATE()
GO

Step 4:
– Session 2
SET TRANSACTION ISOLATION LEVEL SNAPSHOT
BEGIN TRAN
SELECT ModifiedDate
FROM HumanResources.Shift
GO

and I see the updated records!! Why? Dreadfully, I tried SET READ_COMMITTED_SNAPSHOT ON/OFF. It appears to be following Lost Update. I’m using SQLServer2008.

Great post. I hope this comment/question is not ‘too late’ …

Every transaction that needs to use snapshot isolation level has to configure it explicitly before it begins with ‘SET TRANSACTION ISOLATION LEVEL SNAPSHOT’, right? Setting ‘ALLOW_SNAPSHOT_ISOLATION’ on database level is not enough, but required of course?
My point is if you want to use a snapshot isolation across your existing application you can not simply turn it on … code changes required for all tranactions.

In SQL Server 2008, if I understand correctly, setting a ‘READ_COMMITTED_SNAPSHOT’ (under default READ_COMMITTED isolation) on db level is enough? That way no code changes are required.
But READ_COMMITTED_SNAPSHOT allows multi-versioning for single statement(s) only (while SNAPSHOT isolation level does it for entire transaction).

I’d like to hear your opinion … Thank you.

2. You have application where few tables present 80-90% of all data and being hit periodically (by SELECTs and UPDATEs). every UPDATE/INSERT on such table may take seconds which will cause others to stay in waiting list.

These are examples from my own experience.

Good luck!

I have a database that’s been added to for the past 10-15 years and at this point contains tables with a massive amounts of indexes and various apps hitting the db go at the data from a slightly different angle, resulting in a lot of deadlocks.

I’ve been working for a while now in a production control project. The system is responsible of tracking every parcel that is running around in our factory. When ever parcel is transferred from a location to another it’s location must be updated to the DB. This, of course, means heck load of updates to some tables.

So to prevent locking issues with reads/writes we enabled snapshot isolation level and we don’t have to worry about lock storms anymore :)