arangosh> db.ids.ensureIndex({ type: "skiplist", fields: [ "myId" ], unique: true }); { "deduplicate" : true, "fields" : [ "myId" ], "id" : "ids/18595", "isNewlyCreated" : true, "sparse" : false, "type" : "skiplist", "unique" : true, "code" : 201 } arangosh> db.ids.save({ "myId": 123 }); { "_id" : "ids/18598", "_key" : "18598", "_rev" : "_XGh_Zc6--_" } arangosh> db.ids.save({ "myId": 456 }); { "_id" : "ids/18602", "_key" : "18602", "_rev" : "_XGh_Zd---_" } arangosh> db.ids.save({ "myId": 789 }); { "_id" : "ids/18605", "_key" : "18605", "_rev" : "_XGh_ZdC--_" } arangosh> db.ids.save({ "myId": 123 }); [ArangoError 1210: unique constraint violated - in index 18595 of type skiplist over ["myId"]; conflicting key: 18598]