DatabaseService that uses Copycat Raft to provide a strongly consistent and durable database.
diff --git a/core/store/dist/src/main/java/org/onlab/onos/store/service/PreconditionFailedException.java b/core/store/dist/src/main/java/org/onlab/onos/store/service/PreconditionFailedException.java
new file mode 100644
index 0000000..f16fc47
--- /dev/null
+++ b/core/store/dist/src/main/java/org/onlab/onos/store/service/PreconditionFailedException.java
@@ -0,0 +1,14 @@
+package org.onlab.onos.store.service;
+
+/**
+ * Exception that indicates a precondition failure.
+ * <ul>Scenarios that can cause this exception:
+ * <li>An operation that attempts to write a new value iff the current value is equal
+ * to some specified value.</li>
+ * <li>An operation that attempts to write a new value iff the current version
+ * matches a specified value</li>
+ * </ul>
+ */
+@SuppressWarnings("serial")
+public class PreconditionFailedException extends DatabaseException {
+}