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From Vinayakumar B <vinayakum...@apache.org>
Subject Re: [DISCUSS] Allow continue reading from being-written file using same stream
Date Thu, 18 Sep 2014 18:06:15 GMT
bq. I don't know about the merits of this, but I do know that native
filesystems
implement this by not raising the EOF exception on the seek() but only on
the read ... some of the non-HDFS filesystems Hadoop support work this way.

I agree with you steve. read only will throw EOF. But when we know that
file is being written  and it can have fresh data, then polling can be done
by calling available(). later we can continue read or call seek.

One simple example use case is tailing a file.

Regards,
Vinay

On Thu, Sep 18, 2014 at 3:35 PM, Steve Loughran <stevel@hortonworks.com>
wrote:

> I don't know about the merits of this, but I do know that native
> filesystems implement this by not raising the EOF exception on the seek()
> but only on the read ... some of the non-HDFS filesystems Hadoop support
> work this way.
>
> -I haven't ever looked to see what code assumes that it is the seek that
> fails, not the read.
> -PositionedReadable had better handle this too, even if it isn't done via a
> seek()-read()-seek() sequence
>
>
> On 18 September 2014 08:48, Vinayakumar B <vinayakumarb@apache.org> wrote:
>
> > Hi all,
> >
> > Currently *DFSInputStream *doen't allow reading a write-inprogress file,
> > once all written bytes, by the time of opening an input stream, are read.
> >
> > To read further update on the same file, needs to be read by opening
> > another stream to the same file again.
> >
> > Instead how about refreshing length of such open files if the current
> > position is at earlier EOF.
> >
> > May be this could be done in *available() *method, So that clients who
> > knows that original writer will not close then read can continuously poll
> > for new data using the same stream?
> >
> > PS: This is possible in local disk read using FileInputStream
> >
> > Regards,
> > Vinay
> >
>
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