HOLDLOCK with UPDLOCK

Question

It appears using either HOLDLOCK or UPDLOCK in a transaction (say T1), will not block read access from another transaction (say T2).

As I u

Answer 1

I believe Martin already explained how the updlock can result in an exclusive lock (+1)... and I would rather post this as a comment / question, but my comment is too large...

Here's a quick example of the updlock resulting in the x lock...

IF (OBJECT_ID('tblTest') IS NOT NULL)
    DROP TABLE tblTest

CREATE TABLE tblTest (
    ID INT NOT NULL
)

BEGIN TRANSACTION
    SELECT * FROM dbo.tblTest WITH (UPDLOCK, HOLDLOCK) WHERE ID = 1
    SELECT * FROM sys.dm_tran_locks WHERE request_session_id = @@SPID 
COMMIT

However, if you add a clustered index to your table, the exclusive table lock goes away, and is replaced with a RangeS-U lock...

ALTER TABLE dbo.tblTest 
ADD CONSTRAINT PK_tblTest 
PRIMARY KEY CLUSTERED (ID)

BEGIN TRANSACTION
    SELECT * FROM dbo.tblTest WITH (UPDLOCK, HOLDLOCK) WHERE ID = 1
    SELECT * FROM sys.dm_tran_locks WHERE request_session_id = @@SPID 
COMMIT

So basically, do you have a clustered index on this table?

EDIT:

Another example using a non-clustered index...

IF (OBJECT_ID('tblTest') IS NOT NULL)
    DROP TABLE tblTest

CREATE TABLE tblTest (
    ID INT NOT NULL
)

CREATE NONCLUSTERED INDEX 
IX_tblTest ON dbo.tblTest (ID) 

BEGIN TRANSACTION
    SELECT * FROM dbo.tblTest WITH (HOLDLOCK) WHERE ID = 1
    SELECT * FROM sys.dm_tran_locks WHERE request_session_id = @@SPID 
COMMIT

Will result in a RangeS-S lock...

But...

BEGIN TRANSACTION
    SELECT * FROM dbo.tblTest WITH (UPDLOCK, HOLDLOCK) WHERE ID = 1
    SELECT * FROM sys.dm_tran_locks WHERE request_session_id = @@SPID 
COMMIT

Will result in an exclusive table lock...