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https://issues.apache.org/jira/browse/FLINK-26799?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17511536#comment-17511536
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Roman Khachatryan commented on FLINK-26799:
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Hi [~Feifan Wang] , thanks for looking into it,
> But the if condition is incorrect, stream.getPos() return the position of
> underlying stream which is different from position of input.
Exactly, this is the underlying stream that needs to be positioned. Then
"offset" bytes are skipped from the buffer. So I think this is correct.
> Actually, input is aways at position 0 at beginning, so I think we can seek
> to the offset directly.
Are you proposing to seek on the underlying stream {*}before wrapping{*}?
I think that won't work, because the compression flag is written at the
beginning.
Alternatively, seeking on the underlying stream *after wrapping* seem dangerous
to me: there is no contract that no bytes are buffered by constructor AFAIK.
> StateChangeFormat#read not seek to offset correctly
> ---------------------------------------------------
>
> Key: FLINK-26799
> URL: https://issues.apache.org/jira/browse/FLINK-26799
> Project: Flink
> Issue Type: Bug
> Components: Runtime / State Backends
> Reporter: Feifan Wang
> Priority: Major
>
> StateChangeFormat#read must seek to offset before read, current implement as
> follows :
>
> {code:java}
> FSDataInputStream stream = handle.openInputStream();
> DataInputViewStreamWrapper input = wrap(stream);
> if (stream.getPos() != offset) {
> LOG.debug("seek from {} to {}", stream.getPos(), offset);
> input.skipBytesToRead((int) offset);
> }{code}
> But the if condition is incorrect, stream.getPos() return the position of
> underlying stream which is different from position of input.
> By the way, because of wrapped by BufferedInputStream, position of underlying
> stream always at n*bufferSize or the end of file.
> Actually, input is aways at position 0 at beginning, so I think we can seek
> to the offset directly.
>
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