Add support SNAPSHOT isolation level.

3 files changed, 21 insertions, 0 deletions

diff --git a/src/main/java/com/amazon/carbonado/IsolationLevel.java b/src/main/java/com/amazon/carbonado/IsolationLevel.java
index 5f963b2..7571205 100644
--- a/src/main/java/com/amazon/carbonado/IsolationLevel.java
+++ b/src/main/java/com/amazon/carbonado/IsolationLevel.java
@@ -26,6 +26,7 @@ package com.amazon.carbonado;
  * <li>{@link #READ_UNCOMMITTED}

  * <li>{@link #READ_COMMITTED}

  * <li>{@link #REPEATABLE_READ}

+ * <li>{@link #SNAPSHOT}

  * <li>{@link #SERIALIZABLE}

  * </ul>

  *

@@ -35,6 +36,11 @@ package com.amazon.carbonado;
  * iteration. It releases locks during iteration rather than holding on to them

  * until the transaction exits.

  *

+ * <p>{@code SNAPSHOT} isolation is special in that it uses multiversion

+ * concurrency control (MVCC). A commit may fail with an {@link

+ * OptimisticLockException}. Few repositories are expected to support this

+ * level, however.

+ *

  * @author Brian S O'Neill

  * @see Repository#enterTransaction(IsolationLevel)

  * @see Transaction

@@ -73,6 +79,13 @@ public enum IsolationLevel {
 

     /**

      * Indicates that dirty reads, non-repeatable reads and phantom reads are

+     * prevented. Commits can still fail however, as snapshot isolation avoids

+     * using locks.

+     */

+    SNAPSHOT,

+

+    /**

+     * Indicates that dirty reads, non-repeatable reads and phantom reads are

      * prevented. Phantoms are records returned as a result of a search, but

      * which were not seen by the same transaction when the identical search

      * criteria was previously used. For example, another transaction may have

diff --git a/src/main/java/com/amazon/carbonado/OptimisticLockException.java b/src/main/java/com/amazon/carbonado/OptimisticLockException.java
index 2a782d1..b4a43de 100644
--- a/src/main/java/com/amazon/carbonado/OptimisticLockException.java
+++ b/src/main/java/com/amazon/carbonado/OptimisticLockException.java
@@ -21,6 +21,8 @@ package com.amazon.carbonado;
 /**

  * An OptimisticLockException is thrown if the {@link Repository} is using

  * optimistic locking for concurrency control, and lock aquisition failed.

+ * This exception may also be thrown if multiversion concurrency control (MVCC)

+ * is being used and the commit fails.

  *

  * @author Brian S O'Neill

  */

diff --git a/src/main/java/com/amazon/carbonado/repo/jdbc/JDBCRepository.java b/src/main/java/com/amazon/carbonado/repo/jdbc/JDBCRepository.java
index 6e53354..97be915 100644
--- a/src/main/java/com/amazon/carbonado/repo/jdbc/JDBCRepository.java
+++ b/src/main/java/com/amazon/carbonado/repo/jdbc/JDBCRepository.java
@@ -92,6 +92,9 @@ public class JDBCRepository
             return Connection.TRANSACTION_READ_COMMITTED;

         case REPEATABLE_READ:

             return Connection.TRANSACTION_REPEATABLE_READ;

+        case SNAPSHOT:

+            // TODO: not accurate for all databases.

+            return Connection.TRANSACTION_SERIALIZABLE;

         case SERIALIZABLE:

             return Connection.TRANSACTION_SERIALIZABLE;

         }

@@ -117,6 +120,9 @@ public class JDBCRepository
             case REPEATABLE_READ:

                 desiredLevel = IsolationLevel.SERIALIZABLE;

                 break;

+            case SNAPSHOT:

+                desiredLevel = IsolationLevel.SERIALIZABLE;

+                break;

             case SERIALIZABLE: default:

                 return null;

             }