Details
Critical Description
Now that we have Online Merge capabilities, the function of that tool should be extended to make it much easier for HBase operations folks to use. Currently it is a very manual process (one fraught with confusion) to hand pick two regions that are contiguous to each other in the META table such that the admin can manually request those two regions to be merged.
In the real world, when admins find themselves wanting to merge regions, it's usually because they've greatly increased their hbase.hregion.max.filesize property and they have way too many regions on a table and want to reduce the region count for that entire table quickly and easily.
Why can't the OnlineMerge command just take a "-max" argument along with a table name which tells it to go ahead and merge all regions of said table until the resulting regions are all of max size? This takes the voodoo out of the process and quickly gets the admin what they're looking for.
As part of this improvement, I also suggest a "-regioncount" argument for OnlineMerge, which will attempt to reduce the table's region count down to the specified #.