arangosh> db.ids.ensureIndex({ type: "skiplist", fields: [ "myId" ], unique: true }); { "deduplicate" : true, "fields" : [ "myId" ], "id" : "ids/18297", "isNewlyCreated" : true, "sparse" : false, "type" : "skiplist", "unique" : true, "code" : 201 } arangosh> db.ids.save({ "myId": 123 }); { "_id" : "ids/18300", "_key" : "18300", "_rev" : "_WgE9ZQG--_" } arangosh> db.ids.save({ "myId": 456 }); { "_id" : "ids/18304", "_key" : "18304", "_rev" : "_WgE9ZQK--_" } arangosh> db.ids.save({ "myId": 789 }); { "_id" : "ids/18307", "_key" : "18307", "_rev" : "_WgE9ZQO--_" } arangosh> db.ids.save({ "myId": 123 }); [ArangoError 1210: unique constraint violated - in index 18297 of type skiplist over ["myId"]; conflicting key: 18300]