set transaction isolation level read committed
alter database mydatabase set read_committed_snapshot on

From the Sql Server docs :
"Row versioning is used to present each statement within the transaction
with a transactionally consistent snapshot of the data as it existed at the
start of the statement.  Locks are not used to protet the data from updates
by other transactions."

But given that read queries can have complex execution plans, how can the
server know the set of rows that need to be versioned without blocking all
other transactions and figuring it out ( which would be the same as using
shared locks ) ????