arangosh> db.ids.ensureIndex({ type: "skiplist", fields: [ "myId" ], unique: true }); { "deduplicate" : true, "fields" : [ "myId" ], "id" : "ids/111537", "isNewlyCreated" : true, "sparse" : false, "type" : "skiplist", "unique" : true, "code" : 201 } arangosh> db.ids.save({ "myId": 123 }); { "_id" : "ids/111540", "_key" : "111540", "_rev" : "_YQtDtJO--_" } arangosh> db.ids.save({ "myId": 456 }); { "_id" : "ids/111544", "_key" : "111544", "_rev" : "_YQtDtJS--_" } arangosh> db.ids.save({ "myId": 789 }); { "_id" : "ids/111547", "_key" : "111547", "_rev" : "_YQtDtJS--B" } arangosh> db.ids.save({ "myId": 123 }); [ArangoError 1210: unique constraint violated - in index 111537 of type skiplist over ["myId"]; conflicting key: 111540]