predicate locking

Hi
I am having a debate with one of the Postgres developers (Tom Lane)
according to him ms-sql does not implement predicate
locking(SERIALIZABLE).
Where predicate locking is defined as (from the postgres help):
"12.2.2.1. Serializable Isolation versus True Serializability"
It states: "To guarantee true mathematical serializability, it is
necessary for a database system to enforce predicate locking, which
means that a transaction cannot insert or modify a row that would have
matched the WHERE condition of a query in another concurrent
transaction"
Now I put it to him that that is exactly what SERIALIZABLE does in
MS-SQL.
But his response was "Only for WHERE conditions that can be expressed
as a simple range constraint."
Now is he correct i.e SERIALIZABLE works "Only for WHERE conditions
that can be expressed as a simple range constraint." ?
Regards,
Daniel Roth
MCSD.NET
Depends on how you want to quantify it. What is a Range Lock? It is the
demarcation of the begining and the end of records within an Index that
satisfies a particular Where condition. That is for a simple condition that
can be satisfied by an explicit index; however, given a more complex
condition, the range locks can be placed on the Clustered Index that would
satisfy a range of conditions.
However, it is true that there is no "true" predicate locking behavior in
SQL Server. But do not be dismayed, no commercial vendor does so either.
It would have to BLOCK, not lock, upon examination of each subsequently
submitted query to "test" whether or not there may be a logical overlap
between the initiated transaction and any subsequently requested
transaction.
Mathematical Locking is nice, but it is theoretical. A lock is where the
rubber meets the road, and some form of physical lock must be acquired.
That does not mean that it can not be done, but I have failed to see any
real implementations suggested that make practical sense.
Sincerely,
Anthony Thomas

"Daniel Roth" <Daniel Roth@.discussions.microsoft.com> wrote in message
news:7E778689-BEDD-49C4-9ADA-7261222E7593@.microsoft.com...
Hi
I am having a debate with one of the Postgres developers (Tom Lane)
according to him ms-sql does not implement predicate
locking(SERIALIZABLE).
Where predicate locking is defined as (from the postgres help):
"12.2.2.1. Serializable Isolation versus True Serializability"
It states: "To guarantee true mathematical serializability, it is
necessary for a database system to enforce predicate locking, which
means that a transaction cannot insert or modify a row that would have
matched the WHERE condition of a query in another concurrent
transaction"
Now I put it to him that that is exactly what SERIALIZABLE does in
MS-SQL.
But his response was "Only for WHERE conditions that can be expressed
as a simple range constraint."
Now is he correct i.e SERIALIZABLE works "Only for WHERE conditions
that can be expressed as a simple range constraint." ?
Regards,
Daniel Roth
MCSD.NET