+1 to add this module On Wed, Feb 17, 2016 at 9:21 AM, Priyanka Gugale <[email protected]> wrote:
> We need partitions for parallel read but how will the reader partition know > which offset of the file it should read from. Normally FileSplitter creates > this metadata, let's call them as reader task, and forwards them to next > operator which is block reader. Block reader will receive one of the tasks > and read from specified offset in file. If FileSplitter is absent one > reader partition will have to consume one file entirely, which means we > can't have parallel reading over one file. I hope this answers your > question. > > Advantage of having this module is having a reusable component made up of > operators which are frequently used together to do file reading. > > -Priyanka > > On Wed, Feb 17, 2016 at 11:31 AM, Yogi Devendra <[email protected]> > wrote: > > > Let me rephrase Ram's question to make it clear: > > > > For an application developer using Malhar: > > What are the advantages / disadvantages of using the proposed HDFS File > > input Module as compared to directly using FileSplitter, BlockReader > > Operators available in Malhar? > > > > ~ Yogi > > > > On 16 February 2016 at 21:56, Munagala Ramanath <[email protected]> > > wrote: > > > > > Can parallel read not be achieved by partitioning ? > > > > > > Ram > > > > > > On Tue, Feb 16, 2016 at 1:01 AM, Priyanka Gugale < > > [email protected] > > > > > > > wrote: > > > > > > > Hi, > > > > > > > > It is a common usecase to read big files on HDFS in parallel fashion > > i.e. > > > > many reader thread are used to read the file in parallel. We can > > achieve > > > > this on top of Apex using following Malhar operators: > > > > > > > > 1. AbstractFileSplitter > > > > 2. AbstractBlockReader > > > > > > > > where FileSplitter, as per file metadata, creates small reader > tasks(to > > > > read file in parts). Those reader tasks are run by BlockReaders in > > > parallel > > > > to read the file. > > > > > > > > As these operators are generally used together to achieve file read > > > > operation, I propose we create a module, called HDFSFileReader for > > this. > > > > > > > > Please provide your suggestions on same. > > > > > > > > -Priyanka > > > > > > > > > >
