Mongodb Memory Size and Data Size Relationship

  mongodb, question

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Is this Size the best in memory?
When will have data size, index size, storage size
But what is that 5.95G horse that is much bigger than the sum of the above? .
The memory is larger than 5.95g g.
Or is it larger than Data Size (or plus index data size)?

1. If all the data can be stored in memory, of course it is best.
2. database = payload + index
3. MongoDB journal opens 2 ~ 3G by default and can be reduced with –small-files
4. At least the index should be kept in memory.