MongoDB里collection状态的userFlags和systemFlags 是什么意思？

[ns] => test.people
            [count] => 47
            [size] => 8
            [avgObjSize] => 0.17021276595745
            [storageSize] => 12
            [numExtents] => 1
            [nindexes] => 1
            [lastExtentSize] => 12
            [paddingFactor] => 1
            [systemFlags] => 1
            [userFlags] => 0
            [totalIndexSize] => 7
            [indexSizes] => Array
                (
                    [_id_] => 7
                )

            [ok] => 1

高手能否给详解一下。这些数据分别是什么，代表了数据库怎么样的运行状况，谢谢！！！

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参见官方文档，一Google就出来了。 http://docs.mongodb.org/manual/reference/command/collStats/#collStats.systemFlags