Columnar storage for index structure

[gfl94]

We can integrate IndexManger together with CacheManager, IndexManager use a bytebuffer for IndexInfo storage, and CacheManager use a column store for CacheData and CacheInfo, perhaps we can put them together?

[dongx-psu]

No, this is not the case. I mean we can give users a choice to replace the Array[InternalRow] in IPartition to columnar format like the original Spark SQL cache mechanism.