Re: MapFile.Reader and seek

[Tom White <to...@cloudera.com>]

You can use the get() method to seek and retrieve the value. It will
return null if the key is not in the map. Something like:

Text value = (Text) indexReader.get(from, new Text());
while (value != null && ...)

Tom

On Thu, Jan 29, 2009 at 10:45 PM, schnitzi
<ma...@fastsearch.com> wrote:
>
> Greetings all...  I have a situation where I want to read a range of keys and
> values out of a MapFile.  So I have something like this:
>
>    MapFile.Reader indexReader = new MapFile.Reader(fs, path.toString(),
> configuration)
>    boolean seekSuccess = indexReader.seek(from);
>    boolean readSuccess = indexReader.next(keyValue, value);
>    while (readSuccess && ...)
>
> The problem seems to be that while seekSuccess is returning true, when I
> call next() to get the value there, it's returning the value *after* the key
> that I called seek() on.  So if, say, my keys are Text("id0") through
> Text("id9"), and I seek for Text("id3"), calling next() will return
> Text("id4") and its associated value, not Text("id3").
>
> I would expect next() to return the key/value at the seek location, not the
> one after it.  Am I doing something wrong?  Otherwise, what good is seek(),
> really?
> --
> View this message in context: http://www.nabble.com/MapFile.Reader-and-seek-tp21737717p21737717.html
> Sent from the Hadoop core-user mailing list archive at Nabble.com.
>
>

Re: MapFile.Reader and seek

[schnitzi <ma...@fastsearch.com>]

Thanks, Tom -- that seems to work for the case where the "from" value I'm
looking for exists in the MapFile.  However, if I call get() on a "from"
value that doesn't exist, then call next(), I would expect to get the first
value that follows "from", but instead it seems to return the value after
that.

However, after some experimenting I found that getClosest() followed by
next() seems to work.

I would suggest that for both get() and getClosest(), there is nothing in
the javadoc to indicate that subsequent reads will get the values that
follow, so perhaps this could stand a little cleanup or clarification in a
later version.  Also, I still don't see how the seek() method is of much use
(except maybe internally).  But thanks for leading me to a solution for my
particular issue...



Tom White-3 wrote:
> 
> You can use the get() method to seek and retrieve the value. It will
> return null if the key is not in the map. Something like:
> 
> Text value = (Text) indexReader.get(from, new Text());
> while (value != null && ...)
> 
> Tom
> 
> On Thu, Jan 29, 2009 at 10:45 PM, schnitzi
> <ma...@fastsearch.com> wrote:
>>
>> Greetings all...  I have a situation where I want to read a range of keys
>> and
>> values out of a MapFile.  So I have something like this:
>>
>>    MapFile.Reader indexReader = new MapFile.Reader(fs, path.toString(),
>> configuration)
>>    boolean seekSuccess = indexReader.seek(from);
>>    boolean readSuccess = indexReader.next(keyValue, value);
>>    while (readSuccess && ...)
>>
>> The problem seems to be that while seekSuccess is returning true, when I
>> call next() to get the value there, it's returning the value *after* the
>> key
>> that I called seek() on.  So if, say, my keys are Text("id0") through
>> Text("id9"), and I seek for Text("id3"), calling next() will return
>> Text("id4") and its associated value, not Text("id3").
>>
>> I would expect next() to return the key/value at the seek location, not
>> the
>> one after it.  Am I doing something wrong?  Otherwise, what good is
>> seek(),
>> really?
>> --
>> View this message in context:
>> http://www.nabble.com/MapFile.Reader-and-seek-tp21737717p21737717.html
>> Sent from the Hadoop core-user mailing list archive at Nabble.com.
>>
>>
> 
> 

-- 
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