+1 to Robert. Either this will be a Beam-specific file format (and then nothing except Beam will be able to read it - which I doubt is what you want), or it is an existing well-known file format and then we should just develop an IO for it. Note that any file format that involves encoding elements with a Coder is Beam-specific, because wire format of coders is Beam-specific.
On Tue, Jan 31, 2017 at 12:20 PM Robert Bradshaw <rober...@google.com.invalid> wrote: > On Tue, Jan 31, 2017 at 12:04 PM, Aviem Zur <aviem...@gmail.com> wrote: > > +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. > > What would the format of the file be? Just the concatenation of the > elements encoded according to the coder? Or is there a delimiter > needed to separate records. In which case how does one ensure the > delimiter does not also appear in the middle of an encoded element? At > this point you're developing a file format, and might as well stick > with one of the standard ones. https://xkcd.com/927 > > > 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 > >> > > > > > > >> > > > > > >> > > > > >> > > > >> > > >> >
