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External Article

In-Memory OLTP: Row Visibility in SQL Server’s MVCC

SQL Server's In-memory OLTP is fast, due to its multi-valued concurrency control (MVCC). MVCC avoids the need for locks by arranging for each user connected to the database to see a snapshot of the rows of the tables at a point in time, No changes made by the user will be seen by other users of the database until the changes have been completed and committed. It is conceptually simple but does the user always see the correct version of a row under all circumstances? Shel Burkow explains.

2016-10-17

3,150 reads

External Article

DELETE Operation in SQL Server HEAPs

You should stick to using tables in SQL Server, rather than heaps that have no clustered index, unless you have well-considered reasons to choose heaps. However, there are uses for heaps in special circumstances, and it is useful to know what these uses are, and when you should avoid heaps. Uwe Ricken explains, and demonstrates why you'd be unwise to use heaps rather than tables when the data is liable to change.

2016-10-14

3,646 reads

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Question of the Day

Changing the Schema

I set up a few users on my SQL Server 2022 instance.

CREATE LOGIN User1 WITH PASSWORD = 'Demo12#1'
CREATE USER User1 FOR LOGIN User1
GO
CREATE LOGIN User2 WITH PASSWORD = 'Demo12#2'
CREATE USER User2 FOR LOGIN User2
GO
CREATE LOGIN User3 WITH PASSWORD = 'Demo12#3'
CREATE USER User3 FOR LOGIN User3
GO
I then created a schema that one of them owned. Under this schema, I added a table with some data.
CREATE SCHEMA MySchema AUTHORIZATION User1
GO
CREATE TABLE Myschema.MyTable(myid INT)
GO
INSERT MySchema.MyTable
(
    myid
)
VALUES
(1), (2), (3)
GO
SELECT * FROM MySchema.MyTable
GO
I granted rights and verified that User2 could access this table.
GRANT SELECT ON Myschema.MyTable TO User2
GO
SETUSER 'USER2'
GO
SELECT * FROM MySchema.MyTable
GO
This worked. Now, I move this schema to a new user.
ALTER AUTHORIZATION ON SCHEMA::Myschema TO User3;
GO
What happens with this code?
SETUSER 'USER2'
GO
SELECT * FROM MySchema.MyTable
GO

See possible answers