+1 for cleaning up the documentation +1 for adding a link to the documentation (should be a permalink) +1 for printing a warning instead of an exception
On Sun, Jun 21, 2015 at 12:25 AM, Robert Metzger <rmetz...@apache.org> wrote: > We could also add a link to the documentation into the exception that > explains the behavior. > > On Fri, Jun 19, 2015 at 5:52 AM, Chiwan Park <chiwanp...@icloud.com> > wrote: > > > +1 for ignoring execute() call with warning. > > > > But I'm concerned for how the user catches the error in program without > > any data sinks. > > > > By the way, eager execution is not well documented in data sinks section > > but is in program > > skeleton section. [1] This makes the user’s confusion. We should clean up > > documents. > > There are many codes calling execute() method after print() method. > [2][3] > > > > We should add a description for count() method to documents too. > > > > [1] > > > http://ci.apache.org/projects/flink/flink-docs-master/apis/programming_guide.html#data-sinks > > [2] > > > http://ci.apache.org/projects/flink/flink-docs-master/apis/programming_guide.html#parallel-execution > > [3] > > > http://ci.apache.org/projects/flink/flink-docs-master/apis/programming_guide.html#iteration-operators > > > > Regards, > > Chiwan Park > > > > > On Jun 19, 2015, at 9:15 PM, Maximilian Michels <m...@apache.org> > wrote: > > > > > > Dear Flink community, > > > > > > I have stopped to count how many people on the user list and during > Flink > > > trainings have asked why their Flink program throws an Exception when > > they > > > just one to print a DataSet. The reason for this is that print() now > > > executes eagerly, thus, executes the Flink program. Subsequent calls to > > > execute() need to define new DataSinks and throw an exception > otherwise. > > > > > > We have recently introduced a flag in the ExecutionEnvironment that > > checks > > > whether the user executed before (explicitly via execute() or > implicitly > > > through collect()/print()/count()). That enabled us to print a nicer > > > exception message. However, users either do not read the exception > > message > > > or do not understand it. They do ask this question a lot. > > > > > > That's why I propose to ignore calls to execute() entirely if no sinks > > are > > > defined. That will get rid of one of the core annoyances for Flink > > users. I > > > know, that this is painfully for us programmers because we understand > how > > > Flink works internally but let's step back once and see that it > wouldn't > > be > > > so bad if execute didn't do anything in case of no new sinks. > > > > > > What would be the downside of this change? Users might call execute() > and > > > wonder that nothing happens. We would then simply print a warning that > > > their program didn't define any sinks. That is a big difference to the > > > behavior before because users are scared of exceptions. If they just > get > > a > > > warning they will double-check their program and investigate why > nothing > > > happens. Most of the cases they do actually have defined sinks but > simply > > > left a call to execute() when they were printing a DataSet. > > > > > > What are you opinions on this issue? I have opened a JIRA for this as > > well: > > > https://issues.apache.org/jira/browse/FLINK-2249 > > > > > > Best, > > > Max > > > > > > > > > > >
