数组元素在MongoDB中的插入顺序

我无法保存批量插入到mongodb中的插入顺序。

我的应用程序需要连续发送数据（通过HTTP POST @每秒一次）到服务器。 在服务器端，HTTP POST被处理，并且这个数据被存储在mongodb v2.4中的capped集合中。 这个封顶收集的大小很大（50MB）。 这个数据的格式是JSON，它有这样的数组：

{"Data":[{"Timestamp":"2014-08-02 13:38:18:852","Rabbit":[{"a":-0.0010663296561688185,"c":-0.0021321268286556005,"b":-0.0010663296561688185}],"Monkec":[{"a":17.511783599853516,"c":-0.42092469334602356,"b":-0.42092469334602356}]},{"Timestamp":"2014-08-02 13:38:18:858","Rabbit":[{"a":-0.0021321268286556005,"c":-0.0010663296561688185,"b":0.0010657970560714602}],"Monkec":[{"a":9.892329216003418,"c":-0.2339634746313095,"b":-0.2342628538608551}]},{"Timestamp":"2014-08-02 13:38:18:863","Rabbit":[{"a":-0.0010663296561688185,"c":-0.0021321268286556005,"b":0.0021315941121429205}],"Monkec":[{"a":9.702523231506348,"c":-0.24264541268348694,"b":-0.2148033082485199}]},{"Timestamp":"2014-08-02 13:38:18:866","Rabbit":[{"a":-0.0010663296561688185,"c":-0.0010663296561688185,"b":0.0010657970560714602}],"Monkec":[{"a":9.665101051330566,"c":-0.23366409540176392,"b":-0.2197430431842804}]},{"Timestamp":"2014-08-02 13:38:18:868","Rabbit":[{"a":-0.0021321268286556005,"c":-0.0010663296561688185,"b":0.0010657970560714602}],"Monkec":[{"a":9.693991661071777,"c":-0.2936892807483673,"b":-0.22857467830181122}]},{"Timestamp":"2014-08-02 13:38:18:872","Rabbit":[{"a":-0.0010663296561688185,"c":-0.0010663296561688185,"b":0.0010657970560714602}],"Monkec":[{"a":9.684710502624512,"c":-0.2296224981546402,"b":-0.13786330819129944}]},{"Timestamp":"2014-08-02 13:38:18:873","Rabbit":[{"a":-0.0021321268286556005,"c":-0.0010663296561688185,"b":0.0010657970560714602}],"Monkec":[{"a":9.67707633972168,"c":-0.31255003809928894,"b":-0.1902543604373932}]},{"Timestamp":"2014-08-02 13:38:18:875","Rabbit":[{"a":-0.0021321268286556005,"c":-0.0010663296561688185,"b":0}],"Monkec":[{"a":9.739496231079102,"c":-0.1899549812078476,"b":-0.18845809996128082}]},{"Timestamp":"2014-08-02 13:38:18:878","Rabbit":[{"a":-0.003197923768311739,"c":-0.0010663296561688185,"b":0.0010657970560714602}],"Monkec":[{"a":9.721234321594238,"c":-0.19205063581466675,"b":-0.17318984866142273}]},{"Timestamp":"2014-08-02 13:38:18:881","Rabbit":[{"a":-0.003197923768311739,"c":-0.003197923768311739,"b":0.0010657970560714602}],"Monkec":[{"a":9.78545093536377,"c":-0.2501298487186432,"b":-0.1953437775373459}]},{"Timestamp":"2014-08-02 13:38:18:882","Rabbit":[{"a":0,"c":-0.0010663296561688185,"b":0.0021315941121429205}],"Monkec":[{"a":9.686058044433594,"c":-0.21630020439624786,"b":-0.18247054517269135}]},{"Timestamp":"2014-08-02 13:38:18:884","Rabbit":[{"a":-0.0010663296561688185,"c":0,"b":0.0010657970560714602}],"Monkec":[{"a":9.67198657989502,"c":-0.18546432256698608,"b":-0.23156845569610596}]},{"Timestamp":"2014-08-02 13:38:18:887","Rabbit":[{"a":-0.0010663296561688185,"c":-0.0010663296561688185,"b":0.0010657970560714602}],"Monkec":[{"a":9.640103340148926,"c":-0.23276595771312714,"b":-0.25686585903167725}]},{"Timestamp":"2014-08-02 13:38:18:889","Rabbit":[{"a":-0.0010663296561688185,"c":0,"b":0}],"Monkec":[{"a":9.739346504211426,"c":-0.19130218029022217,"b":-0.22602996230125427}]},{"Timestamp":"2014-08-02 13:38:18:891","Rabbit":[{"a":-0.0021321268286556005,"c":-0.0010663296561688185,"b":0}],"Monkec":[{"a":9.716594696044922,"c":-0.22543121874332428,"b":-0.19728973507881165}]},{"Timestamp":"2014-08-02 13:38:18:898","Rabbit":[{"a":-0.0010663296561688185,"c":-0.0010663296561688185,"b":0.0010657970560714602}],"Monkec":[{"a":9.682914733886719,"c":-0.28680360317230225,"b":-0.1740879863500595}]},{"Timestamp":"2014-08-02 13:38:18:904","Rabbit":[{"a":-0.0010663296561688185,"c":0,"b":0.0021315941121429205}],"Monkec":[{"a":9.693093299865723,"c":-0.20866607129573822,"b":-0.2586621046066284}]},{"Timestamp":"2014-08-02 13:38:18:907","Rabbit":[{"a":-0.0021321268286556005,"c":-0.0010663296561688185,"b":0}],"Monkec":[{"a":9.690997123718262,"c":-0.18681152164936066,"b":-0.23216719925403595}]},{"Timestamp":"2014-08-02 13:38:18:910","Rabbit":[{"a":-0.003197923768311739,"c":-0.0010663296561688185,"b":0.0010657970560714602}],"Monkec":[{"a":9.671688079833984,"c":-0.15388000011444092,"b":-0.2588118016719818}]},{"Timestamp":"2014-08-02 13:38:19:055","Rabbit":[{"a":-0.0010663296561688185,"c":-0.0010663296561688185,"b":0}],"Monkec":[{"a":9.689650535583496,"c":-0.23605911433696747,"b":-0.1989363133907318}]}],"Serial":"35689"} 

我使用批量插入命令将其插入到mongodb（使用NodeJs MongoClient驱动程序）中：

  var length = 20; // only doing 20 inserts for testing purposes for (var i = 0; i <length;i++) { var bulk = col.initializeUnorderedBulkOp(); bulk.insert(data["Data"][i]); // data is my JSON data of interest bulk.execute(function(err) { if (err) { return cb(err); } if (++inserted == length) { cb(); // callback (not seen in this code snippet) } }); // end function } // end of for loop 

但是，当我检查数据库中的条目时，它们不是按照数据驻留在原始JSON数组中的顺序插入的。 我的源数据是按升序时间戳顺序排列的，但是mongodb上限集合中的一些条目出现故障。 比如，我看到这个：

 { "Timestamp" : "2014-08-02 13:38:18:910", "Rabbit" : [ { "a" : -0.003197923768311739, "c" : -0.0010663296561688185, "b" : 0.0010657970560714602 } ], "Monkec" : [ { "a" : 9.671688079833984, "c" : -0.15388000011444092, "b" : -0.2588118016719818 } ], "_id" : ObjectId("548e67a683946a5d25bc6d1a") } { "Timestamp" : "2014-08-02 13:38:18:884", "Rabbit" : [ { "a" : -0.0010663296561688185, "c" : 0, "b" : 0.0010657970560714602 } ], "Monkec" : [ { "a" : 9.67198657989502, "c" : -0.18546432256698608, "b" : -0.23156845569610596 } ], "_id" : ObjectId("548e67a683946a5d25bc6d13") } { "Timestamp" : "2014-08-02 13:38:18:904", "Rabbit" : [ { "a" : -0.0010663296561688185, "c" : 0, "b" : 0.0021315941121429205 } ], "Monkec" : [ { "a" : 9.693093299865723, "c" : -0.20866607129573822, "b" : -0.2586621046066284 } ], "_id" : ObjectId("548e67a683946a5d25bc6d18") } 

所以Timestamp“：”2014-08-02 13：38：18：910被存储在“Timestamp”：“2014-08-02 13：38：18：884”之前，即使它在源JSON 。

如何确保mongodb以正确的顺序插入数据？ 我也试过非批量插入（db.col.insert或db.col.insertOne），但仍然得到这种不一致。 谢谢

Answer 1

如果你的查询没有要求任何特定的sorting/sorting，MongoDB不保证它们将以什么顺序返回。

你如何插入你的数据是无关紧要的。 你需要做的就是写下你的find查询：

 // Sort by ascending timestamp db.my_collection.find({ ... }).sort({"TimeStamp": 1}) 

请参阅http://docs.mongodb.org/manual/reference/method/cursor.sort/#cursor.sort获取更多关于如何sorting的信息。

当然，如果你想这样做的话，你可以通过在你的集合上添加一个Timestamp索引来获得很大的好处（参见http://docs.mongodb.org/manual/core/indexes/ ）。