what is a isolation level,is it a concept in EJB or a RDBMS concept?

[senthil sen]

what is an isolation level?
Is it a concept in EJB or a RDBMS concept?

[Chris Mathews]

Isolation is one of the four properties of ACID Transactions. Both EJB and RDBMS systems are concerned with transactions and therefore isolation levels are found in both.
The isolation level defines how independent a transaction is from other transactions in the system. The isolation level is primarily concerned with zero or more of the following conditions:

Dirty Reads

Repeatable Reads

Phantom Reads

EJB allows for four different isolation levels:

Read Uncommitted

Read Committed - prevents Dirty Reads

Repeatable Reads - prevents Dirty Reads and allows Repeatable Reads

Serializable - prevents Dirty Reads, allows Repeatable Reads, and prevents Phantom Reads.

See any of the numerous books available on EJB for a more in depth description.
[ January 19, 2003: Message edited by: Chris Mathews ]