Cheolsoo Park created PIG-3809:
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Summary: AddForEach optimization doesn't set the alias of the
added foreach
Key: PIG-3809
URL: https://issues.apache.org/jira/browse/PIG-3809
Project: Pig
Issue Type: Bug
Components: impl
Reporter: Cheolsoo Park
Assignee: Cheolsoo Park
Fix For: 0.13.0
AddForEach inserts a foreach operator into the plan, but it doesn't set the
alias of added foreach. This is usually okay, but if the foreach is followed by
a join, the missing alias confuses Pig.
For eg, consider the following query (dummy example to demonstrate the issue)-
{code}
a = LOAD 'foo' AS (x, y, z);
b = LOAD 'bar' AS (i, j, k);
c = JOIN a BY x, b BY i;
d = FOREACH c GENERATE a::x, b::i;
DUMP d;
{code}
Without AddForEach optimization, the output schema of 'c' will be as follows-
{code}
a::x, a::y, a::z, b::i, b::j, b::k
{code}
But since 'a::y', 'a::z', 'b::j', and 'b::k' are not used in 'd', a foreach
operator will be inserted after a and b. That is-
{code}
a = LOAD 'foo' AS (x, y, z);
? = FOREACH a GENERATE x; -- no alias is set
b = LOAD 'bar' AS (i, j, k);
? = FOREACH a GENERATE i; -- no alias is set
c = JOIN ? BY x, ? BY i;
d = FOREACH c GENERATE ?::x, ?::i;
DUMP d;
{code}
But due to missing aliases of these added foreach operators, the output schema
of join is messed up. In fact, they show up as null, so printing the output
schema of join gives 'null::x, null::i'.
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