Hi Thomas, Sorry for the delay. I agree that the watermark concept is general and is understood by intermediate transformations. File name is some additional information in the watermark which helps the start and end operators do stuff related to batch. As suggested, I have created a wordcount application which uses watermarks to create separate windows for each file by means of a long (timestamp). I am linking the source for reference:
Watermarks: https://github.com/bhupeshchawda/apex-malhar/blob/batch-io-operators/library/src/main/java/org/apache/apex/malhar/lib/window/windowable/FileWatermark.java Extended File Input and Output operators: https://github.com/bhupeshchawda/apex-malhar/blob/batch-io-operators/library/src/main/java/org/apache/apex/malhar/lib/window/windowable/WindowedFileInputOperator.java https://github.com/bhupeshchawda/apex-malhar/blob/batch-io-operators/library/src/main/java/org/apache/apex/malhar/lib/window/windowable/WindowedFileOutputOperator.java WordCount Application: https://github.com/bhupeshchawda/apex-malhar/blob/batch-io-operators/library/src/test/java/org/apache/apex/malhar/lib/window/windowable/WindowedWordCount.java The input operator attaches a timestamp with each file which allows the WindowedOperator to identify each file and its state in a distinct window. Additionally, using the additional file information, the application can store the counts in similarly named files at the destination. Thanks. _______________________________________________________ Bhupesh Chawda Software Engineer E: [email protected] | Twitter: @bhupeshsc www.datatorrent.com | apex.apache.org On Sat, Feb 18, 2017 at 10:24 PM, Thomas Weise <[email protected]> wrote: > Hi Bhupesh, > > I think this needs a generic watermark concept that is independent of > source and destination and can be understood by intermediate > transformations. File names don't meet this criteria. > > One possible approach is to have a monotonic increasing file sequence > (instead of time, if it is not applicable) that can be mapped to watermark. > You can still tag on the file name to the control tuple as extra > information so that a file output operator that understands it can do > whatever it wants with it. But it should also work without it, let's say > when we write the output to the console. > > The key here is that you can demonstrate that an intermediate stateful > transformation will work. I would suggest to try wordcount per input file > with the window operator that emits the counts at file boundary, without > knowing anything about files. > > Thanks, > Thomas > > > On Sat, Feb 18, 2017 at 8:04 AM, Bhupesh Chawda <[email protected]> > wrote: > > > Hi Thomas, > > > > For an input operator which is supposed to generate watermarks for > > downstream operators, I can think about the following watermarks that the > > operator can emit: > > 1. Time based watermarks (the high watermark / low watermark) > > 2. Number of tuple based watermarks (Every n tuples) > > 3. File based watermarks (Start file, end file) > > 4. Final watermark > > > > File based watermarks seem to be applicable for batch (file based) as > well, > > and hence I thought of looking at these first. Does this seem to be in > line > > with the thought process? > > > > ~ Bhupesh > > > > > > > > _______________________________________________________ > > > > Bhupesh Chawda > > > > Software Engineer > > > > E: [email protected] | Twitter: @bhupeshsc > > > > www.datatorrent.com | apex.apache.org > > > > > > > > On Thu, Feb 16, 2017 at 10:37 AM, Thomas Weise <[email protected]> wrote: > > > > > I don't think this should be designed based on a simplistic file > > > input-output scenario. It would be good to include a stateful > > > transformation based on event time. > > > > > > More complex pipelines contain stateful transformations that depend on > > > windowing and watermarks. I think we need a watermark concept that is > > based > > > on progress in event time (or other monotonic increasing sequence) that > > > other operators can generically work with. > > > > > > Note that even file input in many cases can produce time based > > watermarks, > > > for example when you read part files that are bound by event time. > > > > > > Thanks, > > > Thomas > > > > > > > > > On Wed, Feb 15, 2017 at 4:02 AM, Bhupesh Chawda < > [email protected] > > > > > > wrote: > > > > > > > For better understanding the use case for control tuples in batch, I > > am > > > > creating a prototype for a batch application using File Input and > File > > > > Output operators. > > > > > > > > To enable basic batch processing for File IO operators, I am > proposing > > > the > > > > following changes to File input and output operators: > > > > 1. File Input operator emits a watermark each time it opens and > closes > > a > > > > file. These can be "start file" and "end file" watermarks which > include > > > the > > > > corresponding file names. The "start file" tuple should be sent > before > > > any > > > > of the data from that file flows. > > > > 2. File Input operator can be configured to end the application > after a > > > > single or n scans of the directory (a batch). This is where the > > operator > > > > emits the final watermark (the end of application control tuple). > This > > > will > > > > also shutdown the application. > > > > 3. The File output operator handles these control tuples. "Start > file" > > > > initializes the file name for the incoming tuples. "End file" > watermark > > > > forces a finalize on that file. > > > > > > > > The user would be able to enable the operators to send only those > > > > watermarks that are needed in the application. If none of the options > > are > > > > configured, the operators behave as in a streaming application. > > > > > > > > There are a few challenges in the implementation where the input > > operator > > > > is partitioned. In this case, the correlation between the start/end > > for a > > > > file and the data tuples for that file is lost. Hence we need to > > maintain > > > > the filename as part of each tuple in the pipeline. > > > > > > > > The "start file" and "end file" control tuples in this example are > > > > temporary names for watermarks. We can have generic "start batch" / > > "end > > > > batch" tuples which could be used for other use cases as well. The > > Final > > > > watermark is common and serves the same purpose in each case. > > > > > > > > Please let me know your thoughts on this. > > > > > > > > ~ Bhupesh > > > > > > > > > > > > > > > > On Wed, Jan 18, 2017 at 12:22 AM, Bhupesh Chawda < > > > [email protected]> > > > > wrote: > > > > > > > > > Yes, this can be part of operator configuration. Given this, for a > > user > > > > to > > > > > define a batch application, would mean configuring the connectors > > > (mostly > > > > > the input operator) in the application for the desired behavior. > > > > Similarly, > > > > > there can be other use cases that can be achieved other than batch. > > > > > > > > > > We may also need to take care of the following: > > > > > 1. Make sure that the watermarks or control tuples are consistent > > > across > > > > > sources. Meaning an HDFS sink should be able to interpret the > > watermark > > > > > tuple sent out by, say, a JDBC source. > > > > > 2. In addition to I/O connectors, we should also look at the need > for > > > > > processing operators to understand some of the control tuples / > > > > watermarks. > > > > > For example, we may want to reset the operator behavior on arrival > of > > > > some > > > > > watermark tuple. > > > > > > > > > > ~ Bhupesh > > > > > > > > > > On Tue, Jan 17, 2017 at 9:59 PM, Thomas Weise <[email protected]> > > wrote: > > > > > > > > > >> The HDFS source can operate in two modes, bounded or unbounded. If > > you > > > > >> scan > > > > >> only once, then it should emit the final watermark after it is > done. > > > > >> Otherwise it would emit watermarks based on a policy (files names > > > etc.). > > > > >> The mechanism to generate the marks may depend on the type of > source > > > and > > > > >> the user needs to be able to influence/configure it. > > > > >> > > > > >> Thomas > > > > >> > > > > >> > > > > >> On Tue, Jan 17, 2017 at 5:03 AM, Bhupesh Chawda < > > > > [email protected]> > > > > >> wrote: > > > > >> > > > > >> > Hi Thomas, > > > > >> > > > > > >> > I am not sure that I completely understand your suggestion. Are > > you > > > > >> > suggesting to broaden the scope of the proposal to treat all > > sources > > > > as > > > > >> > bounded as well as unbounded? > > > > >> > > > > > >> > In case of Apex, we treat all sources as unbounded sources. Even > > > > bounded > > > > >> > sources like HDFS file source is treated as unbounded by means > of > > > > >> scanning > > > > >> > the input directory repeatedly. > > > > >> > > > > > >> > Let's consider HDFS file source for example: > > > > >> > In this case, if we treat it as a bounded source, we can define > > > hooks > > > > >> which > > > > >> > allows us to detect the end of the file and send the "final > > > > watermark". > > > > >> We > > > > >> > could also consider HDFS file source as a streaming source and > > > define > > > > >> hooks > > > > >> > which send watermarks based on different kinds of windows. > > > > >> > > > > > >> > Please correct me if I misunderstand. > > > > >> > > > > > >> > ~ Bhupesh > > > > >> > > > > > >> > > > > > >> > On Mon, Jan 16, 2017 at 9:23 PM, Thomas Weise <[email protected]> > > > wrote: > > > > >> > > > > > >> > > Bhupesh, > > > > >> > > > > > > >> > > Please see how that can be solved in a unified way using > windows > > > and > > > > >> > > watermarks. It is bounded data vs. unbounded data. In Beam for > > > > >> example, > > > > >> > you > > > > >> > > can use the "global window" and the final watermark to > > accomplish > > > > what > > > > >> > you > > > > >> > > are looking for. Batch is just a special case of streaming > where > > > the > > > > >> > source > > > > >> > > emits the final watermark. > > > > >> > > > > > > >> > > Thanks, > > > > >> > > Thomas > > > > >> > > > > > > >> > > > > > > >> > > On Mon, Jan 16, 2017 at 1:02 AM, Bhupesh Chawda < > > > > >> [email protected] > > > > >> > > > > > > >> > > wrote: > > > > >> > > > > > > >> > > > Yes, if the user needs to develop a batch application, then > > > batch > > > > >> aware > > > > >> > > > operators need to be used in the application. > > > > >> > > > The nature of the application is mostly controlled by the > > input > > > > and > > > > >> the > > > > >> > > > output operators used in the application. > > > > >> > > > > > > > >> > > > For example, consider an application which needs to filter > > > records > > > > >> in a > > > > >> > > > input file and store the filtered records in another file. > The > > > > >> nature > > > > >> > of > > > > >> > > > this app is to end once the entire file is processed. > > Following > > > > >> things > > > > >> > > are > > > > >> > > > expected of the application: > > > > >> > > > > > > > >> > > > 1. Once the input data is over, finalize the output file > > from > > > > >> .tmp > > > > >> > > > files. - Responsibility of output operator > > > > >> > > > 2. End the application, once the data is read and > > processed - > > > > >> > > > Responsibility of input operator > > > > >> > > > > > > > >> > > > These functions are essential to allow the user to do higher > > > level > > > > >> > > > operations like scheduling or running a workflow of batch > > > > >> applications. > > > > >> > > > > > > > >> > > > I am not sure about intermediate (processing) operators, as > > > there > > > > >> is no > > > > >> > > > change in their functionality for batch use cases. Perhaps, > > > > allowing > > > > >> > > > running multiple batches in a single application may require > > > > similar > > > > >> > > > changes in processing operators as well. > > > > >> > > > > > > > >> > > > ~ Bhupesh > > > > >> > > > > > > > >> > > > On Mon, Jan 16, 2017 at 2:19 PM, Priyanka Gugale < > > > > [email protected] > > > > >> > > > > > >> > > > wrote: > > > > >> > > > > > > > >> > > > > Will it make an impression on user that, if he has a batch > > > > >> usecase he > > > > >> > > has > > > > >> > > > > to use batch aware operators only? If so, is that what we > > > > expect? > > > > >> I > > > > >> > am > > > > >> > > > not > > > > >> > > > > aware of how do we implement batch scenario so this might > > be a > > > > >> basic > > > > >> > > > > question. > > > > >> > > > > > > > > >> > > > > -Priyanka > > > > >> > > > > > > > > >> > > > > On Mon, Jan 16, 2017 at 12:02 PM, Bhupesh Chawda < > > > > >> > > > [email protected]> > > > > >> > > > > wrote: > > > > >> > > > > > > > > >> > > > > > Hi All, > > > > >> > > > > > > > > > >> > > > > > While design / implementation for custom control tuples > is > > > > >> > ongoing, I > > > > >> > > > > > thought it would be a good idea to consider its > usefulness > > > in > > > > >> one > > > > >> > of > > > > >> > > > the > > > > >> > > > > > use cases - batch applications. > > > > >> > > > > > > > > > >> > > > > > This is a proposal to adapt / extend existing operators > in > > > the > > > > >> > Apache > > > > >> > > > > Apex > > > > >> > > > > > Malhar library so that it is easy to use them in batch > use > > > > >> cases. > > > > >> > > > > > Naturally, this would be applicable for only a subset of > > > > >> operators > > > > >> > > like > > > > >> > > > > > File, JDBC and NoSQL databases. > > > > >> > > > > > For example, for a file based store, (say HDFS store), > we > > > > could > > > > >> > have > > > > >> > > > > > FileBatchInput and FileBatchOutput operators which allow > > > easy > > > > >> > > > integration > > > > >> > > > > > into a batch application. These operators would be > > extended > > > > from > > > > >> > > their > > > > >> > > > > > existing implementations and would be "Batch Aware", in > > that > > > > >> they > > > > >> > may > > > > >> > > > > > understand the meaning of some specific control tuples > > that > > > > flow > > > > >> > > > through > > > > >> > > > > > the DAG. Start batch and end batch seem to be the > obvious > > > > >> > candidates > > > > >> > > > that > > > > >> > > > > > come to mind. On receipt of such control tuples, they > may > > > try > > > > to > > > > >> > > modify > > > > >> > > > > the > > > > >> > > > > > behavior of the operator - to reinitialize some metrics > or > > > > >> finalize > > > > >> > > an > > > > >> > > > > > output file for example. > > > > >> > > > > > > > > > >> > > > > > We can discuss the potential control tuples and actions > in > > > > >> detail, > > > > >> > > but > > > > >> > > > > > first I would like to understand the views of the > > community > > > > for > > > > >> > this > > > > >> > > > > > proposal. > > > > >> > > > > > > > > > >> > > > > > ~ Bhupesh > > > > >> > > > > > > > > > >> > > > > > > > > >> > > > > > > > >> > > > > > > >> > > > > > >> > > > > > > > > > > > > > > > > > > > >
