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Wat is isolation level and when do u use them?
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Answer Posted / ram
Specifies the transaction isolation levels that provide the
necessary
consistency and concurrency control between transactions in
the job and
other transactions for optimal performance.
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 reads and phantoms. Use one
of the following
transaction isolation levels:
Read Committed. Takes exclusive locks on modified data and
sharable locks
on all other data. Each query executed by a transaction
sees only data
that was committed before the query (not the transaction)
began. Oracle
queries never read dirty, that is, uncommitted data. This
is the default.
Serializable. Takes exclusive locks on modified data and
sharable locks on
all other data. It sees only those changes committed when
the transaction
began plus those made by the transaction itself through
INSERT, UPDATE,
and DELETE statements. Serializable transactions do not
experience
nonrepeatable reads or phantoms.
Read-only. Sees only those changes that were committed when
the
transaction began. This level does not permit INSERT,
UPDATE, and DELETE
statements.
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