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Hadoop, mail # general - can one map instance handle many data of input paths at the same time

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Re: can one map instance handle many data of input paths at the same time
lei liu 2011-01-21, 05:57
Thanks everyone,

I detailed describe my question.  There are two input
direcoties:/user/test1/ and /user/test2/ path, I want to join the two
direcoties content, in order to join the two directories, I need to identity
the content from which directory, so I use below code in mapper:

    private int tag = -1;
    public void configure(JobConf conf) {
        try {

            this.conf = conf;
            String pathsToAliasStr = conf.get("paths.to.alias");//example:
conf.set("paths.to.alias", "0=/user/test1/,1=/user/test2/"
            String[] pathsToAlias = pathsToAliasStr.split(",");

            Path fpath = new Path((new
            String path = fpath.toUri().toString();

            for (int i = 0; i < pathsToAlias.length; i++) {
                String[] pathToAlias = pathsToAlias[i].split("=");
                if (path.startsWith(pathToAlias[1])) {
                    tag = Integer.valueOf(pathToAlias[0].trim());//identity
current map instatnce are handling which directory content.
        } catch (Throwable e) {
            throw new RuntimeException(e);


So when map method  run,  the content are handled by the mapper are
identified for same direcoty.

I want to know whether one mapper instatnce only handle content of one
directory at same time.

2011/1/21 Eric Sammer <[EMAIL PROTECTED]>

> LiuLei:
> Yes. What you're looking for is TextInputFormat.addPath() (assuming you're
> talking about text). You can call this multiple times and add multiple
> input
> paths if they are all of the same data format (i.e. text). If you have
> multiple paths that contain different format data, you'll need to use
> MultipleInputs. See the javadoc for details on usage.
> On Thu, Jan 20, 2011 at 1:52 AM, lei liu <[EMAIL PROTECTED]> wrote:
> > There are two input paths, example: /user/test1/ and /user/test2/ path.
> >  Can
> > one map instance handle many data of input paths at the same time?
> >
> >
> > Thanks,
> >
> > LiuLei
> >
> --
> Eric Sammer
> twitter: esammer
> data: www.cloudera.com