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https://issues.apache.org/jira/browse/GIRAPH-277?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13428451#comment-13428451
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Eli Reisman commented on GIRAPH-277:
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If you have a use case where this sort of extra preprocessing is needed, and
others think it will be valuable then we should leave it in. If you would be
comfortable putting up something on the wiki documenting for new users how you
think they should go about writing new IO formats, that would be good too.
Actually, given the way the other tools in the Hadoop ecosystem work I don't
think its at all unreasonable to create at least base classes that do 90% of
the work for many common IO formats in use with big data in the Apache
universe, and we use Giraph almost exclusively this way around here. I do think
the current collection has many obvious gaps and we're still a ways from
supplying what people would need. I think a complete basic set would have to
meet the criteria that: 1. a new user could very easily test-drive Giraph with
some of their own sample data without too much trouble, 2. they could use the
supplied IO formats as a guide to writing their own without too much code
duplication or confusion along the way.
> Text Vertex Input/Output Format base classes overhaul
> -----------------------------------------------------
>
> Key: GIRAPH-277
> URL: https://issues.apache.org/jira/browse/GIRAPH-277
> Project: Giraph
> Issue Type: Improvement
> Components: examples, lib
> Reporter: Jaeho Shin
> Attachments: GIRAPH-277.patch
>
>
> The current way of implementing {{VertexInputFormat}} and {{VertexReader}}
> had bad smell. It required users to understand how these two classes are
> glued together, and forced similar codes to be duplicated in every new input
> format. (Similarly for the VertexOutputFormat and VertexWriter.) Anyone who
> wants to create a new format should create an underlying record reader or
> writer at the right moment and delegate some calls to it, which seemed
> unnecessary detail being exposed. Besides, type parameters had to appear all
> over every new format code, which was extremely annoying for both reading
> existing code and writing a new one. I was very frustrated writing my first
> format code especially when I compared it to writing a new vertex code. I
> thought writing a new input/output format should be as simple as vertex.
> So, I have refactored {{TextVertexInputFormat}} and {{OutputFormat}} into new
> forms that have no difference in their interfaces, but remove a lot of burden
> for subclassing. Instead of providing static VertexReader base classes, I
> made it a non-static inner-class of its format class, which helps eliminate
> the repeated code for gluing these two, already tightly coupled classes.
> This has additional advantage of eliminating all the Generics type variables
> on the VertexReader side, which makes overall code much more concise. I
> added several useful TextVertexReader base classes that can save efforts for
> implementing line-oriented formats.
> Please comment if you see my proposed change have any impact on other
> aspects. I'm unsure of how these additional layers of abstraction could
> affect performance.
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