Set AllIsolationLevels

AllIsolationLevels

The predefined set AllIsolationLevels contains the supported isolation levels for a database transaction, as started through the procedure StartTransaction.

Set AllIsolationLevels {
    Index      :  IndexIsolationLevels;
    Definition :  {
        data { ReadUncommitted, ReadCommitted,
               RepeatableRead, Serializable }
    }
}

Definition

The predefined set AllIsolationLevels contains the supported isolation levels for a database transaction. They are:

  • ReadUncommitted: a transaction operating at this level can see uncommitted changes made by other transactions,

  • ReadCommitted (default): a transaction operating at this level cannot see changes made by other transactions until those transactions are committed,

  • RepeatableRead: a transaction operating at this level is guaranteed not to see any changes made by other transactions in values it has already read during the transaction, and

  • Serializable: a transaction operating at this level guarantees that all concurrent transactions interact only in ways that produce the same effect as if each transaction were entirely executed one after the other.

Updatability

The contents of the set cannot be modified.

Note

Not all database servers may support all of these isolation levels, and may cause the call to StartTransaction to fail.

See also

The function StartTransaction.