arangosh> db.ids.ensureIndex({ type: "skiplist", fields: [ "myId" ], unique: true }); { "deduplicate" : true, "fields" : [ "myId" ], "id" : "ids/16418", "isNewlyCreated" : true, "sparse" : false, "type" : "skiplist", "unique" : true, "code" : 201 } arangosh> db.ids.save({ "myId": 123 }); { "_id" : "ids/16421", "_key" : "16421", "_rev" : "_XiAwVRq--_" } arangosh> db.ids.save({ "myId": 456 }); { "_id" : "ids/16425", "_key" : "16425", "_rev" : "_XiAwVRu--_" } arangosh> db.ids.save({ "myId": 789 }); { "_id" : "ids/16428", "_key" : "16428", "_rev" : "_XiAwVRu--B" } arangosh> db.ids.save({ "myId": 123 }); [ArangoError 1210: unique constraint violated - in index 16418 of type skiplist over ["myId"]; conflicting key: 16421]