[PIG-932] Required fields projection in Loader: nested fields in bag/tuple, map key lookup more than two levels

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Duplicate
• Affects Version/s: 0.3.0
• Fix Version/s: 0.8.0
• Component/s: impl
• Assignee: Daniel Dai
• Reporter: Daniel Dai
• Created: 25/Aug/09 23:31
• Updated: 17/Dec/10 22:43
• Resolved: 23/Jul/10 22:59

Description

To leverage the performance features provided by Zebra, Pig should be able to figure out which input fields are actually used in Pig script, and prune unnecessary inputs. This feature is being implementing in PIG-922. However, there are two limitations currently:

1. Pruning nested fields only apply to map. We do not prune sub-field inside a bag or tuple
2. For map, currently we only go one level deep. Eg, if in Pig script, user uses a#'key0'#'key1', a#'key0' will be asked

These two limitations are in line with current limitation of Zebra loader. Once Zebra loader can handle this, we need to work to lift these limitations.