For #3, we already have the following in 1.1 release:

HBASE-10201 Port 'Make flush decisions per column family' to trunk

On Thu, May 5, 2016 at 6:36 PM, Shushant Arora <shushantarora09@gmail.com>
wrote:

> 1.Why is it better to have single file per region than multiple files for
> read performance. Why can't multile threads read multiple file and give
> better performance?
>
> 2Does hbase regionserver has single thread for compactions and split for
> all regions its holding? Why can't single thread per regions will work
> better than sequential compactions/split for all regions in a regionserver.
>
> 3.Why hbase flush and compact all memstores of all the families of a table
> at same time irrespective of their size when even one memstore reaches
> threshold.
>
> Thanks
> Shushant
>