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set transaction [Oracle
set transaction read only; set transaction read write; set transaction isolation level serializable; set transaction isolation level read committed; set transaction use rollback segment some_rollback_segment; set transaction name some_name; set transaction read only name some_name; set transaction read write name some_name; set transaction isolation level serialiazable name some_name; set transaction isolation level read commited name some_name; set transaction use rollback segment some_rollback_segment name some_name;
A read only transaction can not change data, hence the DML statements
The other SQL statements that are allowed in read only transactions are:
A read only transaction doesn't see any changed data whose commit was issued later than the read only transaction has begun. This is called transaction-level read consistency.
This is the default in Oracle. A (possibly long running) statement only sees data that was already commited when the statement has started as opposed to when the transaction has started. This is called statement-level read consistency.
This is the default in Oracle.
This sets the isolation level to serializable.
use rollback segment
This specifies the rollback segment to be used for this transaction. A transaction can not be read only when this clause is used.
Relevant in distributed database environments.
Thanks to Urs Moser who spotted two typos on this page.