Reuven - Is TextIO.read().from() a more complex case than the topic Ismaël is bringing up in this thread? I'm surprised to hear that the two examples have different performance characteristics.
Reading through the implementation, I guess the fundamental difference is whether a given configuration expands to TextIO.ReadAll or to io.Read. AFAICT, that detail and the subsequent performance impact is not documented. If the above is correct, perhaps it's an argument for IOs to provide higher-level methods in cases where they can optimize performance compared to what a user might naively put together. On Wed, Jan 30, 2019 at 12:35 PM Reuven Lax <re...@google.com> wrote: > Jeff, what you did here is not simply a refactoring. These two are quite > different, and will likely have different performance characteristics. > > The first evaluates the wildcard, and allows the runner to pick > appropriate bundling. Bundles might contain multiple files (if they are > small), and the runner can split the files as appropriate. In the case of > the Dataflow runner, these bundles can be further split dynamically. > > The second chops of the files inside the the PTransform, and processes > each chunk in a ParDo. TextIO.readFiles currently chops up each file into > 64mb chunks (hardcoded), and then processes each chunk in a ParDo. > > Reuven > > > On Wed, Jan 30, 2019 at 9:18 AM Jeff Klukas <jklu...@mozilla.com> wrote: > >> I would prefer we move towards option [2]. I just tried the following >> refactor in my own code from: >> >> return input >> .apply(TextIO.read().from(fileSpec)); >> >> to: >> >> return input >> .apply(FileIO.match().filepattern(fileSpec)) >> .apply(FileIO.readMatches()) >> .apply(TextIO.readFiles()); >> >> Yes, the latter is more verbose but not ridiculously so, and it's also >> more instructive about what's happening. >> >> When I first started working with Beam, it took me a while to realize >> that TextIO.read().from() would accept a wildcard. The more verbose version >> involves a method called "filepattern" which makes this much more obvious. >> It also leads me to understand that I could use the same FileIO.match() >> machinery to do other things with filesystems other than read file >> contents. >> >> On Wed, Jan 30, 2019 at 11:26 AM Ismaël Mejía <ieme...@gmail.com> wrote: >> >>> Hello, >>> >>> A ‘recent’ pattern of use in Beam is to have in file based IOs a >>> `readAll()` implementation that basically matches a `PCollection` of >>> file patterns and reads them, e.g. `TextIO`, `AvroIO`. `ReadAll` is >>> implemented by a expand function that matches files with FileIO and >>> then reads them using a format specific `ReadFiles` transform e.g. >>> TextIO.ReadFiles, AvroIO.ReadFiles. So in the end `ReadAll` in the >>> Java implementation is just an user friendly API to hide FileIO.match >>> + ReadFiles. >>> >>> Most recent IOs do NOT implement ReadAll to encourage the more >>> composable approach of File + ReadFiles, e.g. XmlIO and ParquetIO. >>> >>> Implementing ReadAll as a wrapper is relatively easy and is definitely >>> user friendly, but it has an issue, it may be error-prone and it adds >>> more code to maintain (mostly ‘repeated’ code). However `readAll` is a >>> more abstract pattern that applies not only to File based IOs so it >>> makes sense for example in other transforms that map a `Pcollection` >>> of read requests and is the basis for SDF composable style APIs like >>> the recent `HBaseIO.readAll()`. >>> >>> So the question is should we: >>> >>> [1] Implement `readAll` in all file based IOs to be user friendly and >>> assume the (minor) maintenance cost >>> >>> or >>> >>> [2] Deprecate `readAll` from file based IOs and encourage users to use >>> FileIO + `readFiles` (less maintenance and encourage composition). >>> >>> I just checked quickly in the python code base but I did not find if >>> the File match + ReadFiles pattern applies, but it would be nice to >>> see what the python guys think on this too. >>> >>> This discussion comes from a recent slack conversation with Łukasz >>> Gajowy, and we wanted to settle into one approach to make the IO >>> signatures consistent, so any opinions/preferences? >>> >>
