Mailing-List: contact common-user-help@hadoop.apache.org; run by ezmlm
Precedence: bulk
Reply-To: common-user@hadoop.apache.org
Received-SPF: pass (athena.apache.org: domain of murat.migdisoglu@gmail.com
 designates 209.85.213.48 as permitted sender)
MIME-Version: 1.0
Date: Mon, 21 May 2012 19:31:28 +0200
Message-ID: 
 <CAHnriXmpSOwFdADndyyqMPtMxQ9swyjGJF88eG9AQc79gh=YtA@mail.gmail.com>
Subject: Is mapper called per row when used with Cassandra
From: murat migdisoglu <murat.migdisoglu@gmail.com>
To: common-user@hadoop.apache.org
Content-Type: multipart/alternative; boundary=14dae9340fcfad772904c08f457c

--14dae9340fcfad772904c08f457c
Content-Type: text/plain; charset=ISO-8859-1

Hi,

I'm quite new in Hadoop and trying to understand how the task split works
when used with Cassandra ColumnFamilyInputFormat.

I have a very basic scenario: Cassandra has the sessionId and a bson data
that contains the username. I want to go through all rows and dump the row
to a file when the username is matching to a certain criteria. And I do not
need any Reducer or Combiner for now.

After I've written the following very simple hadoop job, I see from the
logs that my mapper function is called per each row.  Is that normal? If
that is the case, doing such a search operation in a big dataset would take
hours if not days...

I guess i need a better understanding on how splitting the job into tasks
works exactly..


    @Override
    public void map(ByteBuffer key, SortedMap<ByteBuffer, IColumn> columns,
Context context)
    throws IOException, InterruptedException
    {
        String rowkey = ByteBufferUtil.string(key);
        String ip = context.getConfiguration().get(IP);
        IColumn column = columns.get(sourceColumn);
        if (column == null)
            return;
        ByteBuffer byteBuffer = column.value();
        ByteBuffer bb2 = byteBuffer.duplicate();

        DataConvertor convertor= fromBson(byteBuffer,
DataConvertor.class);
        String username= convertor.getUsername();
        BytesWritable value = new BytesWritable();
        if (username != null && username.equals(cip)) {
            byte[] arr = convertToByteArray(bb2);
            value.set(new BytesWritable(arr));
            Text tkey = new Text(rowkey);
            context.write( tkey, value);
        } else {
            log.info("ip not match [" + ip + "]");
        }
    }

Thanks in advance
Kind Regards

--14dae9340fcfad772904c08f457c--