arangosh> db.ids.ensureIndex({ type: "skiplist", fields: [ "myId" ], unique: true }); { "deduplicate" : true, "fields" : [ "myId" ], "id" : "ids/74835", "isNewlyCreated" : true, "name" : "idx_1646382081998061568", "selectivityEstimate" : 1, "sparse" : false, "type" : "skiplist", "unique" : true, "code" : 201 } arangosh> db.ids.save({ "myId": 123 }); { "_id" : "ids/74839", "_key" : "74839", "_rev" : "_ZXF6dYC--_" } arangosh> db.ids.save({ "myId": 456 }); { "_id" : "ids/74841", "_key" : "74841", "_rev" : "_ZXF6dYG---" } arangosh> db.ids.save({ "myId": 789 }); { "_id" : "ids/74843", "_key" : "74843", "_rev" : "_ZXF6dYG--A" } arangosh> db.ids.save({ "myId": 123 }); [ArangoError 1210: unique constraint violated - in index idx_1646382081998061568 of type skiplist over 'myId'; conflicting key: 74839]