Chapter 18. Set Up Isolation Levels
18.1. About Isolation Levels
Isolation levels determine when readers can view a concurrent write.
REPEATABLE_READ are the two isolation modes offered in Red Hat JBoss Data Grid.
READ_COMMITTED. This isolation level is applicable to a wide variety of requirements. This is the default value in Remote Client-Server and Library modes.
The only valid value for locks in Remote Client-Server mode is the default
READ_COMMITTEDvalue. The value explicitly specified with the
isolationvalue is ignored.
lockingelement is not present in the configuration, the default isolation value is
For isolation mode configuration examples in JBoss Data Grid, see the lock striping configuration samples:
- See Configure Lock Striping (Remote Client-Server Mode) for a Remote Client-Server mode configuration sample.
- See Configure Lock Striping (Library Mode)for a Library mode configuration sample.
18.2. About READ_COMMITTED
READ_COMMITTED is one of two isolation modes available in Red Hat JBoss Data Grid.
In JBoss Data Grid’s
READ_COMMITTED mode, write operations are made to copies of data rather than the data itself. A write operation blocks other data from being written, however writes do not block read operations. As a result, both
REPEATABLE_READ modes permit read operations at any time, regardless of when write operations occur.
READ_COMMITTED mode multiple reads of the same key within a transaction can return different results due to write operations in different transactions modifying data between reads. This phenomenon is known as non-repeatable reads and is avoided in
18.3. About REPEATABLE_READ
REPEATABLE_READ is one of two isolation modes available in Red Hat JBoss Data Grid.
REPEATABLE_READ does not allow write operations while read operations are in progress, nor does it allow read operations when write operations occur. This prevents the "non-repeatable read" phenomenon, which occurs when a single transaction has two read operations on the same row but the retrieved values differ (possibly due to a write operation modifying the value between the two read operations).
JBoss Data Grid’s
REPEATABLE_READ isolation mode preserves the value of an entry before a modification occurs. As a result, the "non-repeatable read" phenomenon is avoided because a second read operation on the same entry retrieves the preserved value rather than the new modified value. As a result, the two values retrieved by the two read operations in a single transaction will always match, even if a write operation occurs in a different transaction between the two reads.