Being a generic JDBC input format, I would prefer to stay with Row, letting the developer manage the cast according to the driver functionalities.
As for the open() and close() issue, I agree with Flavio that we'd need a better management of the inputformat lifecycle. Perhaps a new interface extending it: RichInputFormat? my2c. Stefano 2016-04-18 9:35 GMT+02:00 Flavio Pompermaier <pomperma...@okkam.it>: > Talking with Stefano this morning and looking at the DataSourceTask code we > discovered that the open() and close() methods are both called for every > split and not once per inputFormat instance (maybe open and close should be > renamed as openSplit and closeSplit to avoid confusion...). > I think that it could worth to add 2 methods to the InputFormat (e.g. > openInputFormat() and closeInputFormat() ) to allow for the managment of > the InputFormat lifecycle, otherwise I'll need to instantiate a pool (and > thus adding a dependency) to avoid the creation of a new connection > (expensive operation) for every split (that in our use case happens > millions of times). > > What about the output of the inputFormat? how do you want me to proceed? > With POJO or Row? If POJO, which strategy do you suggest? > > Best, > Flavio > > On Fri, Apr 15, 2016 at 2:06 PM, Stefano Bortoli <s.bort...@gmail.com> > wrote: > > > If we share the connection, then we should also be careful with the > close() > > implementation. I did not see changes for this method in the PR. > > > > saluti, > > Stefano > > > > 2016-04-15 11:01 GMT+02:00 Flavio Pompermaier <pomperma...@okkam.it>: > > > > > Following your suggestions I've fixed the connection reuse in my PR at > > > https://github.com/apache/flink/pull/1885. > > > I simply check in the establishConnection() if dbConn!=null and, in > that > > > case, I simply return immediately. > > > > > > Thus, the only remaining thin to fix is the null handling. Do you have > > any > > > suggestion about how to transform the results in a POJO? > > > Maybe returning a Row and then let the user manage the conversion to > the > > > target POJO in a successive map could be a more general soloution? > > > > > > Best, > > > Flavio > > > > > > On Thu, Apr 14, 2016 at 6:52 PM, Fabian Hueske <fhue...@gmail.com> > > wrote: > > > > > > > There is an InputFormat object for each parallel task of a > DataSource. > > > > So for a source with parallelism 8 you will have 8 instances of the > > > > InputFormat running, regardless whether this is on one box with 8 > slots > > > or > > > > 8 machines with 1 slots each. > > > > The same is true for all other operators (Map, Reduce, Join, etc.) > and > > > > DataSinks. > > > > > > > > Note, a single task does not fill a slot, but a "slice" of the > program > > > (one > > > > parallel task of each operator) fills a slot. > > > > > > > > Cheers, Fabian > > > > > > > > 2016-04-14 18:47 GMT+02:00 Flavio Pompermaier <pomperma...@okkam.it > >: > > > > > > > > > ok thanks!just one last question: an inputformat is instantiated > for > > > each > > > > > task slot or once for task manger? > > > > > On 14 Apr 2016 18:07, "Chesnay Schepler" <ches...@apache.org> > wrote: > > > > > > > > > > > no. > > > > > > > > > > > > if (connection==null) { > > > > > > establishCOnnection(); > > > > > > } > > > > > > > > > > > > done. same connection for all splits. > > > > > > > > > > > > On 14.04.2016 17:59, Flavio Pompermaier wrote: > > > > > > > > > > > >> I didn't understand what you mean for "it should also be > possible > > to > > > > > reuse > > > > > >> the same connection of an InputFormat across InputSplits, i.e., > > > calls > > > > of > > > > > >> the open() method". > > > > > >> At the moment in the open method there's a call to > > > > establishConnection, > > > > > >> thus, a new connection is created for each split. > > > > > >> If I understood correctly, you're suggesting to create a pool in > > the > > > > > >> inputFormat and simply call poo.borrow() in the open() rather > than > > > > > >> establishConnection? > > > > > >> > > > > > >> On 14 Apr 2016 17:28, "Chesnay Schepler" <ches...@apache.org> > > > wrote: > > > > > >> > > > > > >> On 14.04.2016 17:22, Fabian Hueske wrote: > > > > > >>> > > > > > >>> Hi Flavio, > > > > > >>>> > > > > > >>>> that are good questions. > > > > > >>>> > > > > > >>>> 1) Replacing null values by default values and simply > forwarding > > > > > records > > > > > >>>> is > > > > > >>>> very dangerous, in my opinion. > > > > > >>>> I see two alternatives: A) we use a data type that tolerates > > null > > > > > >>>> values. > > > > > >>>> This could be a POJO that the user has to provide or Row. The > > > > drawback > > > > > >>>> of > > > > > >>>> Row is that it is untyped and not easy to handle. B) We use > > Tuple > > > > and > > > > > >>>> add > > > > > >>>> an additional field that holds an Integer which serves as a > > bitset > > > > to > > > > > >>>> mark > > > > > >>>> null fields. This would be a pretty low level API though. I am > > > > leaning > > > > > >>>> towards the user-provided POJO option. > > > > > >>>> > > > > > >>>> i would also lean towards the POJO option. > > > > > >>> > > > > > >>> 2) The JDBCInputFormat is located in a dedicated Maven module. > I > > > > think > > > > > we > > > > > >>>> can add a dependency to that module. However, it should also > be > > > > > possible > > > > > >>>> to > > > > > >>>> reuse the same connection of an InputFormat across > InputSplits, > > > > i.e., > > > > > >>>> calls > > > > > >>>> of the open() method. Wouldn't that be sufficient? > > > > > >>>> > > > > > >>>> this is the right approach imo. > > > > > >>> > > > > > >>> Best, Fabian > > > > > >>>> > > > > > >>>> 2016-04-14 16:59 GMT+02:00 Flavio Pompermaier < > > > pomperma...@okkam.it > > > > >: > > > > > >>>> > > > > > >>>> Hi guys, > > > > > >>>> > > > > > >>>>> I'm integrating the comments of Chesnay to my PR but there's > a > > > > couple > > > > > >>>>> of > > > > > >>>>> thing that I'd like to discuss with the core developers. > > > > > >>>>> > > > > > >>>>> > > > > > >>>>> 1. about the JDBC type mapping (addValue() method at > [1]: > > At > > > > the > > > > > >>>>> moment > > > > > >>>>> if I find a null value for a Double, the getDouble of > > jdbc > > > > > return > > > > > >>>>> 0.0. > > > > > >>>>> Is > > > > > >>>>> it really the correct behaviour? Wouldn't be better to > > use a > > > > > POJO > > > > > >>>>> or > > > > > >>>>> the > > > > > >>>>> Row of datatable that can handle void? Moreover, the > > mapping > > > > > >>>>> between > > > > > >>>>> SQL > > > > > >>>>> type and Java types varies much from the single JDBC > > > > > >>>>> implementation. > > > > > >>>>> Wouldn't be better to rely on the Java type coming from > > > using > > > > > >>>>> resultSet.getObject() to get such a mapping rather than > > > using > > > > > the > > > > > >>>>> ResultSetMetadata types? > > > > > >>>>> 2. I'd like to handle connections very efficiently > because > > > we > > > > > >>>>> have a > > > > > >>>>> use > > > > > >>>>> case with billions of records and thus millions of > splits > > > and > > > > > >>>>> establish > > > > > >>>>> a > > > > > >>>>> new connection each time could be expensive. Would it > be a > > > > > >>>>> problem to > > > > > >>>>> add > > > > > >>>>> apache pool dependency to the jdbc batch connector in > > order > > > to > > > > > >>>>> reuase > > > > > >>>>> the > > > > > >>>>> created connections? > > > > > >>>>> > > > > > >>>>> > > > > > >>>>> [1] > > > > > >>>>> > > > > > >>>>> > > > > > >>>>> > > > > > >>>>> > > > > > > > > > > > > > > > https://github.com/fpompermaier/flink/blob/FLINK-3750/flink-batch-connectors/flink-jdbc/src/main/java/org/apache/flink/api/java/io/jdbc/JDBCInputFormat.java > > > > > >>>>> > > > > > >>>>> > > > > > >>>>> > > > > > > > > > > > > > > > > > > > > >
