advancedxy

> Introduce the pluggable disk selection strategy. Currently the disk will be selected based on the hash. Free-capacity based strategy should be supported. Agreed. Currently the hash based strategy may...

> Introduce the free space & total space metrics of every local disk @zuston how do you plan to collect these metrics? By using `df`, or any other fancy ways?

I noticed this bug too. We can have a logical plan to represent the Intersect/Except operators. But in the essential, the `intersect all` could be rewrote by primitive operations, such...