HBase and Bigtable support single-row transactions

Question

What does it mean that HBase and Google's Bigtable both support single-row transactions but not multi-row? Currently I am using HBase on top of my local file system; how can I see this practically?

Answer 1

You have a row that looks like this:

username: fabspro password: 1234 account_active: 1 last_login: 2012-10-10 last_login_ip: 135.23.15.3

for example. Then when the user logs in, you need to up date last_login and last_login_ip. If you update both fields in a single put operation, then both fields will update at the same time. If one field cannot be updated for some reason, or if the update fails midway, then neither value will be written. This means that no matter what, if you read that row, you can expect that last_login and last_login_ip are consistent with each other.