Re: Isolation level and Locks

On Fri, 24 Apr 1998 09:12:56 +0200, philippe <philippe_at_arpege.imaginet.fr> wrote:
>What is the default isolation level for oracle ?

(from the Oracle online documentation)

read committed
 This is the default transaction isolation level. Each query executed by a transaction sees only data that was committed before the query (not the transaction) began. An Oracle query will never read dirty (uncommitted) data.

Because Oracle does not prevent other transactions from modifying the data read by a query, that data may be changed by other transactions between two executions of the query. Thus, a transaction that executes a given query twice may experience both nonrepeatable read and phantoms.  

serializable transactions
 Serializable transactions see only those changes that were committed at the time the transaction began, plus those changes made by the transaction itself through INSERT, UPDATE, and DELETE statements. Serializable transactions do not experience nonrepeatable reads or phantoms.  

read-only
 Read-only transactions see only those changes that were committed at the time the transaction began and do not allow INSERT, UPDATE, and DELETE statements  

--

This does not seem to correspond exactly to the four ANSI levels, which I unfortunately do not have handy. The default isolation level for MS SQLServer is different -- serializable.

Joshua Stern
JRStern_at_primalsys.com Received on Fri Apr 24 1998 - 17:56:44 CDT