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https://issues.apache.org/jira/browse/PIG-1085?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12778599#action_12778599
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Alan Gates commented on PIG-1085:
---------------------------------
Documentation for this patch:
The singleton UDFContext class provides two features to UDF writers. First, on
the backend, it allows UDFs to get access to the JobConf object, by calling
getJobConf. This is only available on the backend (at run time) as the JobConf
has not yet been constructed on the front end (during planning time).
Second, it allows UDFs to pass configuration information between instantiations
of the UDF on the front and backends. UDFs can store information in a
configuration object when they are constructed on the front end, or during
other front end calls such as describeSchema. They can then read that
information on the backend when exec (for EvalFunc) or getNext (for LoadFunc)
is called. Note that information will not be passed bewteen instantiations of
the function on the backend. The communication channel only works from front
end to back end.
To store information, the UDF calls getUDFProperties. This returns a
Properties object which the UDF can record the information in or read the
information from. To avoid name space conflicts UDFs are required to provide a
signature when obtaining a Properties object. This can be done in two ways.
The UDF can provide its Class object (via this.getClass()). In this case,
every instantiation of the UDF will be given the same Properties object. The
UDF can also provide its Class plus an array of Strings. The UDF can pass its
constructor arguments, or some other identifying strings. This allows each
instantiation of the UDF to have a different properties object thus avoiding
name space collisions between instantiations of the UDF.
> Pass JobConf and UDF specific configuration information to UDFs
> ---------------------------------------------------------------
>
> Key: PIG-1085
> URL: https://issues.apache.org/jira/browse/PIG-1085
> Project: Pig
> Issue Type: New Feature
> Components: impl
> Reporter: Alan Gates
> Assignee: Alan Gates
> Attachments: udfconf-2.patch, udfconf.patch
>
>
> Users have long asked for a way to get the JobConf structure in their UDFs.
> It would also be nice to have a way to pass properties between the front end
> and back end so that UDFs can store state during parse time and use it at
> runtime.
> This patch does part of what is proposed in PIG-602, but not all of it. It
> does not provide a way to give user specified configuration files to UDFs.
> So I will mark 602 as depending on this bug, but it isn't a duplicate.
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