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From "Jaeho Shin (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (GIRAPH-277) Text Vertex Input/Output Format base classes overhaul
Date Thu, 02 Aug 2012 23:44:02 GMT

    [ https://issues.apache.org/jira/browse/GIRAPH-277?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13427736#comment-13427736
] 

Jaeho Shin commented on GIRAPH-277:
-----------------------------------

Thanks Eli.

It would be great to entirely eliminate the need of writing I/O code and let users pick from
a large collection, but I think that is unlikely if complex data structure is used in the
input graph.  We can easily exhaust the possible combinations of int, double, Text I/O formats,
but Map and List were the types of values and messages mostly in my cases.  I admit some parts
could look over engineered, and don't really reduce the net amount of code, but the big picture
is clearly to make the blanks in the code obvious for users and only ask them to implement
what they really need to.

I didn't have chance to test these text formats on large scale, but I'm using identically
structured format codes for reading and writing Hive tables of >100M rows, ~15GB without
problem.  The holes user needs to fill in this case are how to get vertex id, value and edge
maps from a particular row in the table, instead of a single text line.

About the checkstyle xml, I was reluctant to make the change because it might encourage us
to abuse suppress comments, but thought it was also silly to blow up the xml itself. I'm in
no way a checkstyle expert, and just found [good hints|http://stackoverflow.com/a/4023351/390044]
from the web :)
                
> 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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