From fb3696bc72ce7bcbf17a5188b7fec1c5b690ad23 Mon Sep 17 00:00:00 2001
From: "Brian S. O'Neill" <bronee@gmail.com>
Date: Mon, 2 Oct 2006 06:08:44 +0000
Subject: Add support SNAPSHOT isolation level.

---
 src/main/java/com/amazon/carbonado/IsolationLevel.java      | 13 +++++++++++++
 .../java/com/amazon/carbonado/OptimisticLockException.java  |  2 ++
 .../java/com/amazon/carbonado/repo/jdbc/JDBCRepository.java |  6 ++++++
 3 files changed, 21 insertions(+)

(limited to 'src/main/java/com/amazon')

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
@@ -71,6 +77,13 @@ public enum IsolationLevel {
      */
     REPEATABLE_READ,
 
+    /**
+     * 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
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;
             }
-- 
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