What is read consistency?

What is read consistency?

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Read consistency is one of the purposes that undo data serves. It is a property such that if a user makes some changes against any specific table, and another user simultaneously fires a query against the same table, the changes made by the first referenced user are not visible to the second referenced user who has queried against the table, until the query of the first referenced user is completed or until the first referenced user fires a new query against the table.

By using the SET TRANSACTION statement, read consistency can be applied to an entire table.

Example: SQL > set transaction read only;

The statements that are permitted in a read only transaction are:

• SELECT statement without the FOR UPDATE clause
• LOCK TABLE
• SET ROLE
• ALTER SESSION
• ALTER SYSTEM

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