arangosh> db.ids.ensureIndex({ type: "skiplist", fields: [ "myId" ], unique: true }); { "deduplicate" : true, "fields" : [ "myId" ], "id" : "ids/18240", "isNewlyCreated" : true, "sparse" : false, "type" : "skiplist", "unique" : true, "code" : 201 } arangosh> db.ids.save({ "myId": 123 }); { "_id" : "ids/18243", "_key" : "18243", "_rev" : "_WgE9Wwu--_" } arangosh> db.ids.save({ "myId": 456 }); { "_id" : "ids/18247", "_key" : "18247", "_rev" : "_WgE9Wwy--_" } arangosh> db.ids.save({ "myId": 789 }); { "_id" : "ids/18250", "_key" : "18250", "_rev" : "_WgE9Ww2--_" } arangosh> db.ids.save({ "myId": 123 }); [ArangoError 1210: unique constraint violated - in index 18240 of type skiplist over ["myId"]; conflicting key: 18243]