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From "Rohini Palaniswamy (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (PIG-3655) BinStorage and InterStorage approach to record markers is broken
Date Thu, 20 Jul 2017 14:24:00 GMT

    [ https://issues.apache.org/jira/browse/PIG-3655?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16094759#comment-16094759
] 

Rohini Palaniswamy commented on PIG-3655:
-----------------------------------------

Few comments:
1) Instead of using out.size(), you should making it FSDataOutputStream.getPos() and change
InterRecordWriter to take FSDataOutputStream in the constructor. DataOutputStream.size() is
limited to INTEGER.MAX_VALUE and wraps around on overflow.

2) Can you add a comment explaining the logic
{code}
long expectedReplicateSize = PigConfiguration.PIG_INTERSTORAGE_SYNCMARKER_SIZE_DEFAULT + 2*(1
+1+1)
	                                       + PigConfiguration.PIG_INTERSTORAGE_SYNCMARKER_SIZE_DEFAULT
+ 1*(1 +1);
{code}

I have couple of more questions. Will catch you on chat for those.

> BinStorage and InterStorage approach to record markers is broken
> ----------------------------------------------------------------
>
>                 Key: PIG-3655
>                 URL: https://issues.apache.org/jira/browse/PIG-3655
>             Project: Pig
>          Issue Type: Bug
>    Affects Versions: 0.2.0, 0.3.0, 0.4.0, 0.5.0, 0.6.0, 0.7.0, 0.8.0, 0.8.1, 0.9.0, 0.9.1,
0.9.2, 0.10.0, 0.11, 0.10.1, 0.12.0, 0.11.1
>            Reporter: Jeff Plaisance
>            Assignee: Adam Szita
>         Attachments: PIG-3655.0.patch, PIG-3655.1.patch, PIG-3655.2.patch, PIG-3655.3.patch
>
>
> The way that the record readers for these storage formats seek to the first record in
an input split is to find the byte sequence 1 2 3 110 for BinStorage or 1 2 3 19-21|28-30|36-45
for InterStorage. If this sequence occurs in the data for any reason (for example the integer
16909166 stored big endian encodes to the byte sequence for BinStorage) other than to mark
the start of a tuple it can cause mysterious failures in pig jobs because the record reader
will try to decode garbage and fail.
> For this approach of using an unlikely sequence to mark record boundaries, it is important
to reduce the probability of the sequence occuring naturally in the data by ensuring that
your record marker is sufficiently long. Hadoop SequenceFile uses 128 bits for this and randomly
generates the sequence for each file (selecting a fixed, predetermined value opens up the
possibility of a mean person intentionally sending you that value). This makes it extremely
unlikely that collisions will occur. In the long run I think that pig should also be doing
this.
> As a quick fix it might be good to save the current position in the file before entering
readDatum, and if an exception is thrown seek back to the saved position and resume trying
to find the next record marker.



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