arangosh> db.ids.ensureIndex({ type: "skiplist", fields: [ "myId" ], unique: true }); { "deduplicate" : true, "fields" : [ "myId" ], "id" : "ids/74234", "isNewlyCreated" : true, "name" : "idx_1641835679946113024", "selectivityEstimate" : 1, "sparse" : false, "type" : "skiplist", "unique" : true, "code" : 201 } arangosh> db.ids.save({ "myId": 123 }); { "_id" : "ids/74238", "_key" : "74238", "_rev" : "_ZG8Lmgu--_" } arangosh> db.ids.save({ "myId": 456 }); { "_id" : "ids/74240", "_key" : "74240", "_rev" : "_ZG8Lmgy---" } arangosh> db.ids.save({ "myId": 789 }); { "_id" : "ids/74242", "_key" : "74242", "_rev" : "_ZG8Lmgy--A" } arangosh> db.ids.save({ "myId": 123 }); [ArangoError 1210: unique constraint violated - in index idx_1641835679946113024 of type skiplist over 'myId'; conflicting key: 74238]