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https://issues.apache.org/jira/browse/PIG-1595?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12906116#action_12906116
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Daniel Dai commented on PIG-1595:
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Patch looks good. This patch is to address the problem that we cannot get
output schema of the scalar UDF at compile time. Another approach is write
ReadScalars.outputSchema(), and use the input schema to figure out the output
schema. But again we need to address the dependency to make sure input schema
is correctly set before calling outputSchema(). So both approach should be
equivalent.
> casting relation to scalar- problem with handling of data from non PigStorage
> loaders
> -------------------------------------------------------------------------------------
>
> Key: PIG-1595
> URL: https://issues.apache.org/jira/browse/PIG-1595
> Project: Pig
> Issue Type: Bug
> Reporter: Thejas M Nair
> Assignee: Thejas M Nair
> Fix For: 0.8.0
>
> Attachments: PIG-1595.1.patch
>
>
> If load functions that don't follow the same bytearray format as PigStorage
> for other supported datatypes, or those that don't implement the LoadCaster
> interface are used in 'casting relation to scalar' (PIG-1434), it can cause
> the query to fail or create incorrect results.
> The root cause of the problem is that there is a real dependency between the
> ReadScalars udf that returns the scalar value and the LogicalOperator that
> acts as its input. But the logicalplan does not capture this dependency. So
> in SchemaResetter visitor used by the optimizer, the order in which schema is
> reset and evaluated does not take this into consideration. If the schema of
> the input LogicalOperator does not get evaluated before the ReadScalar udf,
> the resutltype of ReadScalar udf becomes bytearray. POUserFunc will convert
> the input to bytearray using ' new DataByteArray(inp.toString().getBytes())'.
> But this bytearray encoding of other supported types might not be same for
> the LoadFunction associated with the column, and that can result in problems.
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