ABA problem in indexing: https://www.dropbox.com/s/03z14rvqfc4ozc7/Screenshot%202016-11-22%2016.09.10.png?dl=0
Ankita addressed this issue by 9fbf8ed331c3be4a83a4a5d82bba19f3b31ac16a.
I think holding bucket lock during index insertion and deletion is not ideal. The entire bucket will be blocked for ~40us (15 for insert, 10 for sync to backup, 15 for deletion). Even when we are not using indexing, the commit ac16a forces to hold bucket lock during sync to backup.