royans

We discussed Brewer’s Theorm a few days ago and how its challenging to obtain Consistency, Availability and Partition tolerance in any distributed system. We also discussed that many of the distributed datastores allow CAP to be tweaked to attain certain operational goals. Amazon SimpleDB, which was released as an “Eventually Consistent” datastore,  today launched a few features to do just that. Consistent reads : Select and GetAttributes request now include an optional Boolean flag “ConsistentRead” which requests datastore to return consistent results only. If you have noticed scenarios where read right after a write returned an old value, it shouldn’t happen anymore. Conditional put/puts, delete/deletes : By providing “conditions” in the form of a key/value pair SimpleDB can now conditionally execute/discard an operation. This might look like a minor feature, but can go a long way in providing reliable datastore operations. Even though SimpleDB now