Implement multi-row mutations for python Bigtable

[destijl]

It would be great if you could add multi-row mutations to the Bigtable python client library. AFAICS it doesn't exist yet.

The RPC API supports it:
https://cloud.google.com/bigtable/docs/reference/data/rpc/google.bigtable.v2#mutaterowsrequest

It just isn't implemented for python. The first use case I ran into is I have a bunch of rows to delete and a want to make a single RPC to do that, but I'm sure there will be more.

[tseaver]

See #1546.

[destijl]

Thanks, I'm not using happybase but the context manager approach suggested in that bug looks good.

[garye]

Good news: @skyfox is currently working on implementing this

[CuriousDima]

In my current solution, I added mutation class and the new multi rows mutation function as a method of the Table class.

Pros:

1. Easy to use - mutations can be specified outside of rows;
2. No need to construct Row instances. Original RPC call works on a level of row keys.

Cons:

1. new abstraction
2. The Row class should be refactored and work with mutations 3) Mutations for every row should be the same.

Alternative solution. Same new table method. In a method body - extract rows keys/mutations and build request.

Pros:

1. No new abstractions

Cons:

1. Extracting row key from row object
2. Not so easy to use - Rows should be constructed first.

The second way, from my point of view, is closer to the current implementation and would prefer to extended Row class a little. Even with a small overhead for extracting keys from rows.

Any cons?

[garye]

@tseaver , any thoughts on this?

[CuriousDima]

Pull request: #3401

[mbrukman]

@garye, @skyfox: since PR #3401 was merged, can we close this issue, or is there more work left?

[tseaver]

AFAICT, the merge of #3401 should have closed this issue.