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Isolation levels

vikasids sharma
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Joined: Aug 01, 2003
Posts: 157
Please let me know the difference between read committed and read uncommitted isolation levels.
thanks
Vikas


Thanks
Vikas Sharma
SCJP(1.4)
Pradeep bhatt
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Joined: Feb 27, 2002
Posts: 8919

Read Un commited - A transaction will see the uncommited changes made by the concurrently executing transactions.
Read commited - A transaction will see the only the commited changes.


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vikasids sharma
Ranch Hand

Joined: Aug 01, 2003
Posts: 157
if my EJB is using transactions with oracle and i am using read uncomminted isolation level.
Are there chances of dirty read and phantoms?
thanks
Vikas
Originally posted by vikasids sharma:
Please let me know the difference between read committed and read uncommitted isolation levels.
thanks
Vikas
Lasse Koskela
author
Sheriff

Joined: Jan 23, 2002
Posts: 11962
    
    5
if my EJB is using transactions with oracle and i am using read uncomminted isolation level.
Are there chances of dirty read and phantoms?

TRANSACTION_READ_UNCOMMITTED is the least restrictive isolation level (also known as "no isolation"...) so dirty reads and phantom reads are possible.


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vikasids sharma
Ranch Hand

Joined: Aug 01, 2003
Posts: 157
i have read oracle uses read commited as default isolation level.
Does my EJB isolation level(read uncommitted)over rules isolation level of oracle?
Originally posted by Lasse Koskela:

TRANSACTION_READ_UNCOMMITTED is the least restrictive isolation level (also known as "no isolation"...) so dirty reads and phantom reads are possible.
Pradeep bhatt
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Joined: Feb 27, 2002
Posts: 8919

Oracle does not support read uncommited isolation level.
vikasids sharma
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Joined: Aug 01, 2003
Posts: 157
here we are saying oracle does not support read uncommitted.If it so then i dont see any chances of dirty reads and phantoms in context with oracle no matter if i am using read uncommitted isolation of my EJB.
please coorect me if o m wrong.
Originally posted by Pradeep Bhat:
Oracle does not support read uncommited isolation level.

Originally posted by Lasse Koskela:

TRANSACTION_READ_UNCOMMITTED is the least restrictive isolation level (also known as "no isolation"...) so dirty reads and phantom reads are possible.
Lasse Koskela
author
Sheriff

Joined: Jan 23, 2002
Posts: 11962
    
    5
Originally posted by vikasids sharma:
here we are saying oracle does not support read uncommitted.If it so then i dont see any chances of dirty reads and phantoms in context with oracle no matter if i am using read uncommitted isolation of my EJB.

Using TRANSACTION_READ_COMMITTED still allows phantom reads and un-repeatable reads, and TRANSACTION_REPEATABLE_READ allows phantoms as well. You're not completely safe until you go for TRANSACTION_SERIALIZABLE...
 
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subject: Isolation levels