Question

How are compound shard key used to generate new chunks? I mean, if I have a shard key like

{key1 : 1, key2 : 1}

and the collection is being populated as we go, how does MongoDB create the new chunks boundaries given that there are two keys? I can see them in the config server BUT I can not read them. they look like

[min key1,min key2] —> [max key1, max key2]

and many often, min key 2> max key 2. How does that make sense?

In other words, how are the chunks min and max being set on new chunks given the shard key is compound?

key 1 is of type string and key 2 is of type int

I would appreciate it if you could explain it by an example.

Answer 1

The boundary is always from positive to negative infinity. As you insert it will break that initial chunk into smaller ones.

Here is a thread which should answer your question.