arangosh> db.ids.ensureIndex({ type: "skiplist", fields: [ "myId" ], unique: true }); { "deduplicate" : true, "fields" : [ "myId" ], "id" : "ids/111499", "isNewlyCreated" : true, "sparse" : false, "type" : "skiplist", "unique" : true, "code" : 201 } arangosh> db.ids.save({ "myId": 123 }); { "_id" : "ids/111502", "_key" : "111502", "_rev" : "_YOn1gHC--_" } arangosh> db.ids.save({ "myId": 456 }); { "_id" : "ids/111506", "_key" : "111506", "_rev" : "_YOn1gHG--_" } arangosh> db.ids.save({ "myId": 789 }); { "_id" : "ids/111509", "_key" : "111509", "_rev" : "_YOn1gHG--B" } arangosh> db.ids.save({ "myId": 123 }); [ArangoError 1210: - in index 111499 of type skiplist over 'myId'; conflicting key: 111502]