FIX: SERIALIZABLE Isolation Fails When Using Aggregate Functions (198674)

SYMPTOMS

SQL Server 7.0 Books Online documents 'SET TRANSACTION ISOLATION LEVEL SERIALIZABLE' as providing the ability prevent other users from performing data modifications when in a transaction.

A SELECT statement using an aggregate function (such as MIN, MAX, COUNT, AVG, and so on) will not maintain the correct range lock and allows modifications on secondary connections. Setting the transaction isolation level to serializable should maintain the range lock and prevent phantom INSERT, UPDATE, and DELETE operations.

RESOLUTION

A supported fix that corrects this problem is now available from Microsoft, but has not been fully regression tested and should be applied only to systems experiencing this specific problem. If you are not severely affected by this specific problem, Microsoft recommends that you wait for the next SQL Server service pack that contains this fix.

To resolve this problem immediately, contact Microsoft Product Support Services to obtain the fix. For a complete list of Microsoft Product Support Services phone numbers and information on support costs, please go to the following address on the World Wide Web:

http://support.microsoft.com/default.aspx?scid=fh;EN-US;CNTACTMS

The English version of this fix should have the following file attributes or later:

   File name   Platform
   ---------------------

   S70631i.exe (x86)
   S70631a.exe (Alpha)

MORE INFORMATION

For clarity, the following is a sample that demonstrates the behavior.

-- Connection #1
use pubs
go
set transaction isolation level serializable
go
begin transaction
go

--
--  Should BLOCK the second connection but does not
select min(au_lname) from authors
go

-- Connection #2
use pubs
go
set transaction isolation level serializable
go
begin transaction
go
insert into authors (au_id, au_lname, au_fname, contract) values ('000-00-0000', 'aa', 'aa', 1)
go

NOTE: The INSERT should be blocked, but it is allowed to complete. This allows a new row to be introduced in the range that did not exist during the original SELECT operation.