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From "Jacques Nadeau (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DRILL-3516) UDF documentation doesn't get people where they need to be
Date Mon, 20 Jul 2015 16:05:04 GMT

    [ https://issues.apache.org/jira/browse/DRILL-3516?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14633745#comment-14633745
] 

Jacques Nadeau commented on DRILL-3516:
---------------------------------------

My notes to better provide the conceptual overview:

The key thing to understand is that a UDF is slightly incomplete Java.  This is because Drill
actually rips apart the functionality of the UDF and recomposes it directly within expression
evaluation code.  This gives a substantial performance and memory benefit but also creates
some challenges.  As such, there are some key rules one should follow:
 
 - Don't use imports
 - Both class file and source file have to be on the classpath (yes, Drill uses the source
of the function)
 - Any JAR files holding UDF resources must include drill-module.conf marker file so that
Drill knows to include that JAR in consideration for UDF loading
 - ValueHolders should be treated as structs.  As such, don't call any methods on ValueHolders

> UDF documentation doesn't get people where they need to be
> ----------------------------------------------------------
>
>                 Key: DRILL-3516
>                 URL: https://issues.apache.org/jira/browse/DRILL-3516
>             Project: Apache Drill
>          Issue Type: Bug
>            Reporter: Ted Dunning
>
> The UDF documentation on the web side rooted at http://drill.apache.org/docs/develop-custom-functions/
does not describe the high level process for how UDF's are used, nor does it describe why
simple things like toString can't work on *Holder data structures.
> This leads to huge confusion and frustration on the part of potentially contributors.
> Here are some pertinent threads:
> http://mail-archives.apache.org/mod_mbox/drill-user/201507.mbox/%3CCACAwhF%3DBxs-bXNdrm0pNJ4e8hZiaueqtZMhJ%3DRiBpf%3Dt%3DzEOWA%40mail.gmail.com%3E
> http://mail-archives.apache.org/mod_mbox/drill-user/201507.mbox/%3CCACAwhFmwWkP6udc05UEGFTzpEsaRvAxSRKW%2B2Mg-ijYX8QoQxQ%40mail.gmail.com%3E



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