+1 on what Stas said. I think there is value in not having the user write a custom IO for a protocol they use which is not covered by Beam IOs. Plus having them deal with not only the encoding but also the IO part is not ideal. I think having a basic FileIO that can write to the Filesystems supported by Beam (GS/HDFS/Local/...) which you can use any coder with, including your own custom coder, can be beneficial.
On Tue, Jan 31, 2017 at 7:56 PM Stas Levin <stasle...@gmail.com> wrote: I believe the motivation is to have an abstraction that allows one to write stuff to a file in a way that is agnostic to the coder. If one needs to write a non-Avro protocol to a file, and this particular protocol does not meet the assumption made by TextIO, one might need to duplicate the file IO related code from AvroIO. On Tue, Jan 31, 2017 at 6:50 PM Eugene Kirpichov <kirpic...@google.com.invalid> wrote: > Could you clarify why it would be useful to write objects to files using > Beam coders, as opposed to just using e.g. AvroIO? > > Coders (should) make no promise as to what their wire format is, so such > files could be read back only by other Beam pipelines using the same IO. > > On Tue, Jan 31, 2017 at 2:48 AM Aviem Zur <aviem...@gmail.com> wrote: > > > So If I understand the general agreement is that TextIO should not > support > > anything but lines from files as strings. > > I'll go ahead and file a ticket that says the Javadoc should be changed > to > > reflect this and `withCoder` method should be removed. > > > > Is there merit for Beam to supply an IO which does allow writing objects > to > > a file using Beam coders and Beam FS (To write these files to > > GS/Hadoop/Local)? > > > > On Tue, Jan 31, 2017 at 2:28 AM Eugene Kirpichov > > <kirpic...@google.com.invalid> wrote: > > > > P.S. Note that this point (about coders) is also mentioned in the > > now-being-reviewed PTransform Style Guide > > https://github.com/apache/beam-site/pull/134 > > currently staged at > > > > > http://apache-beam-website-pull-requests.storage.googleapis.com/134/contribute/ptransform-style-guide/index.html#coders > > > > > > On Mon, Jan 30, 2017 at 4:25 PM Chamikara Jayalath <chamik...@apache.org > > > > wrote: > > > > > +1 to what Eugene said. > > > > > > I've seen a number of Python SDK users incorrectly assuming that > > > coder.decode() is needed when developing their own file-based sources > > > (since many users usually refer to text source first). Probably coder > > > parameter should not be configurable for text source/sink and they > should > > > be updated to only read/write UTF-8 encoded strings. > > > > > > - Cham > > > > > > On Mon, Jan 30, 2017 at 3:38 PM Eugene Kirpichov > > > <kirpic...@google.com.invalid> wrote: > > > > > > > The use of Coder in TextIO is a long standing design issue because > > coders > > > > are not intended to be used for general purpose converting things > from > > > and > > > > to bytes, their only proper use is letting the runner materialize and > > > > restore objects if the runner thinks it's necessary. IMO it should > have > > > > been called LineIO, document that it reads lines of text as String, > and > > > not > > > > have a withCoder parameter at all. > > > > > > > > The proper way to address your use case is to write a custom > > > > FileBasedSource. > > > > On Mon, Jan 30, 2017 at 2:52 AM Aviem Zur <aviem...@gmail.com> > wrote: > > > > > > > > > The Javadoc of TextIO states: > > > > > > > > > > * <p>By default, {@link TextIO.Read} returns a {@link PCollection} > of > > > > > {@link String Strings}, > > > > > * each corresponding to one line of an input UTF-8 text file. To > > > convert > > > > > directly from the raw > > > > > * bytes (split into lines delimited by '\n', '\r', or '\r\n') to > > > another > > > > > object of type {@code T}, > > > > > * supply a {@code Coder<T>} using {@link > > > TextIO.Read#withCoder(Coder)}. > > > > > > > > > > However, as I stated, `withCoder` doesn't seem to have tests, and > > > > probably > > > > > won't work given the hard-coded '\n' delimiter. > > > > > > > > > > On Mon, Jan 30, 2017 at 12:18 PM Jean-Baptiste Onofré < > > j...@nanthrax.net > > > > > > > > > wrote: > > > > > > > > > > > Hi Aviem, > > > > > > > > > > > > TextIO is not designed to write/read binary file: it's pure Text, > > so > > > > > > String. > > > > > > > > > > > > Regards > > > > > > JB > > > > > > > > > > > > On 01/30/2017 09:24 AM, Aviem Zur wrote: > > > > > > > Hi, > > > > > > > > > > > > > > While trying to use TextIO to write/read a binary file rather > > than > > > > > String > > > > > > > lines from a textual file I ran into an issue - the delimiter > > > TextIO > > > > > uses > > > > > > > seems to be hardcoded '\n'. > > > > > > > See `findSeparatorBounds` - > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > https://github.com/apache/beam/blob/master/sdks/java/core/src/main/java/org/apache/beam/sdk/io/TextIO.java#L1024 > > > > > > > > > > > > > > The use case is to have a file of objects, encoded into bytes > > > using a > > > > > > > coder. However, '\n' is not a good delimiter here, as you can > > > > imagine. > > > > > > > A similar pattern is found in Spark's `saveAsObjectFile` > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > https://github.com/apache/spark/blob/master/core/src/main/scala/org/apache/spark/rdd/RDD.scala#L1512 > > > > > > > where > > > > > > > they use a more appropriate delimiter, to avoid such issues. > > > > > > > > > > > > > > I did not find any unit tests which use TextIO to read anything > > > other > > > > > > than > > > > > > > Strings. > > > > > > > > > > > > > > > > > > > -- > > > > > > Jean-Baptiste Onofré > > > > > > jbono...@apache.org > > > > > > http://blog.nanthrax.net > > > > > > Talend - http://www.talend.com > > > > > > > > > > > > > > > > > > > > >
