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https://issues.apache.org/jira/browse/HBASE-14307?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14715223#comment-14715223
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Chris Nauroth commented on HBASE-14307:
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[~ram_krish] and [~anoop.hbase], thank you for your replies.
Just to add a little more context on Shradha's information, the contract of
[{{FSDataInputStream}}|http://hadoop.apache.org/docs/r2.7.1/api/org/apache/hadoop/fs/PositionedReadable.html]
guarantees that it will read "up to the specified number of bytes". It does
not guarantee that it will read exactly that number of bytes. Even if the
backing file contains that many bytes remaining, a file system implementation
may choose to return immediately after reading any bytes that are already
available in buffer space, without forcing the caller to block waiting for the
exact number of bytes to be available.
This is similar to the contract of
[{{java.io.InputStream}}|http://docs.oracle.com/javase/7/docs/api/java/io/InputStream.html],
which states that "a smaller number may be read".
bq. In many places we use IOUtils.readFully API which in turn will use loop. I
dont think there is some reason why we should not use that here as well.
That sounds like exactly the kind of change we had in mind. It sounds like the
intent of this logic in HBase is to detect premature EOF, not necessarily
demand that a single read call completes the entire operation.
Thank you both!
> Incorrect use of positional read api in HFileBlock
> --------------------------------------------------
>
> Key: HBASE-14307
> URL: https://issues.apache.org/jira/browse/HBASE-14307
> Project: HBase
> Issue Type: Bug
> Reporter: Shradha Revankar
> Priority: Minor
>
> Considering that {{read()}} is not guaranteed to read all bytes,
> I'm interested to understand this particular piece of code and why is partial
> read treated as an error :
> https://github.com/apache/hbase/blob/master/hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/HFileBlock.java#L1446-L1450
> Particularly, if hbase were to use a different filesystem, say
> WebhdfsFileSystem, this would not work, please also see
> https://issues.apache.org/jira/browse/HDFS-8943 for discussion around this.
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