arangosh> db.ids.ensureIndex({ type: "skiplist", fields: [ "myId" ], unique: true }); { "deduplicate" : true, "fields" : [ "myId" ], "id" : "ids/15416", "isNewlyCreated" : true, "sparse" : false, "type" : "skiplist", "unique" : true, "code" : 201 } arangosh> db.ids.save({ "myId": 123 }); { "_id" : "ids/15419", "_key" : "15419", "_rev" : "_VRerC9W---" } arangosh> db.ids.save({ "myId": 456 }); { "_id" : "ids/15423", "_key" : "15423", "_rev" : "_VRerC9a---" } arangosh> db.ids.save({ "myId": 789 }); { "_id" : "ids/15426", "_key" : "15426", "_rev" : "_VRerC9e---" } arangosh> db.ids.save({ "myId": 123 }); [ArangoError 1210: unique constraint violated - in index 15416 of type skiplist over ["myId"]]