Typed map for Pig
-----------------
Key: PIG-1876
URL: https://issues.apache.org/jira/browse/PIG-1876
Project: Pig
Issue Type: New Feature
Components: impl
Reporter: Daniel Dai
Assignee: Daniel Dai
Fix For: 0.9.0
Currently Pig map type is untyped, which means map value is always of
bytearray(ie. unknown) type. In PIG-1277, we allow unknown type to be a shuffle
key, which somewhat relieve the problem. However, typed map is still beneficial
in that:
1. User can make semantic use of the map value type. Currently, user need to
explicitly cast map value, which is ugly
2. Though PIG-1277 allow unknown type be a shuffle key, the performance
suffers. We don't have a raw comparator for the unknown type, instead, we need
to instantiate the value object and invoke its comparator
Here is proposed syntax for typed map:
map[type]
Typed map can be used in place of untyped map could occur. For example:
a = load '1.txt' as(map[int]);
b = foreach a generate (map[(i:int)])a0; - - Map value is tuple
b = stream a through `cat` as (m:map[{(i:int,j:chararray)}]); - - Map value is
bag
MapLookup a typed map will result datatype of map value.
a = load '1.txt' as(map[int]);
b = foreach a generate $0#'key';
Schema for b:
b: {chararray}
The behavior of untyped map will remain the same.
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