SQL Server snapshot isolation level issue

Question

Hello everyone,

I am studying snapshot isolation level of SQL Server 2008 from the below link. My confusion is,

http://msdn.microsoft.com/en-us/library/ms173763.aspx

1. It is mentioned "Data modifications made by other transactions after the start of the current transaction are not visible to statements executing in the current transaction." -- seems data committed by other transactions are not visible to the current snapshot isolation level transaction;

2. It is mentioned "A transaction running under SNAPSHOT isolation level can view changes made by that transaction." -- seems data committed by other transactions are visible to the current snapshot isolation level transaction.

Seems 1 and 2 are conflicting? Any comments?

thanks in advance, George

Answer 1

Number 2 means "I can see my own changes; I can't see other changes"

So if I start a transaction and I make changes, I can see them. Other transactions for other sessions/connections started after my TXN can not see my changes

Answer 2

You also need to know the difference between SNAPSHOT and READ COMMITTED SNAPSHOT - for the latter, you need to modify your quote from BOL as follows:

"Data modifications made by other transactions after the start of the current STATEMENT (not transaction!) are not visible to statements executing in the current transaction."

An example of a case when it makes a big difference: When Snapshot Isolation Helps and When It Hurts