arangosh> db.ids.ensureIndex({ type: "persistent", fields: [ "myId" ], unique: true }); { "deduplicate" : true, "fields" : [ "myId" ], "id" : "ids/74158", "isNewlyCreated" : true, "name" : "idx_1641835679923044352", "selectivityEstimate" : 1, "sparse" : false, "type" : "persistent", "unique" : true, "code" : 201 } arangosh> db.ids.save({ "myId": 123 }); { "_id" : "ids/74162", "_key" : "74162", "_rev" : "_ZG8Lmfa---" } arangosh> db.ids.save({ "myId": 456 }); { "_id" : "ids/74164", "_key" : "74164", "_rev" : "_ZG8Lmfa--A" } arangosh> db.ids.save({ "myId": 789 }); { "_id" : "ids/74166", "_key" : "74166", "_rev" : "_ZG8Lmfa--C" } arangosh> db.ids.save({ "myId": 123 }); [ArangoError 1210: unique constraint violated - in index idx_1641835679923044352 of type persistent over 'myId'; conflicting key: 74162]