Hi, which operators in your application are writing to external systems?
When you look at the example from the blog ( https://github.com/DataTorrent/examples/tree/master/tutorials/exactly-once), there is Kafka input, which is configured to be idempotent. The results are written to JDBC. That operator by itself supports exactly-once through transactions (in conjunction with idempotent input), hence there is no need to configure the processing mode at all. Thomas On Thu, Oct 6, 2016 at 1:52 PM, Bandaru, Srinivas < srinivas.band...@optum.com> wrote: > Thanks Thomas. We have set the set all three operator properties, Kafka > input operator has set to “Exactly_once” and downstream two operators set > as AT_MOST_ONCE same as mentioned in documentation. We have also referred > the documentation you have shared but couldn’t find the right properties > for exactly_once scenario. Is there anything we are missing or need to add > additional properties if someone else used this functionality. > > > > *Any help would be greatly appreciated??* > > > > We tried with different combinations and trying to set all three > properties with “EXACTLY_ONCE”, But application throwing an with error > saying *“If the processing mode for an operator is specified as > EXACTLY_ONCE then the processing mode for all downstream operators should > be specified as AT_MOST_ONCE otherwise it will result in an error.*” > Application behavior is same as the Datatorrent documentation but it’s not > working. > > > > Thanks, > > Srinivas > > > > > > *From:* Thomas Weise [mailto:t...@apache.org] > *Sent:* Thursday, October 06, 2016 3:03 PM > *To:* users@apex.apache.org > *Subject:* Re: Datatorrent fault tolerance > > > > Hi, > > > > It would be necessary to know a bit more about your application for > specific recommendations, but from what I see above, a few things don't > look right. > > > > It appears that you are setting the processing mode on the input operator, > which only reads from Kafka. Exactly-once is important for operators that > affect the state of external systems, for example when writing to a > database, or, producing messages to Kafka. > > > > There is also a problem with the documentation that may contribute to the > confusion. The processing mode you are trying to use isn't really > exactly-once and probably will be deprecated in a future release. Here are > some better resources on fault tolerance and processing semantics: > > > > http://apex.apache.org/docs.html > > https://www.youtube.com/watch?v=FCMY6Ii89Nw > > http://www.slideshare.net/ApacheApexOrganizer/webinar-fault- > toleranceandprocessingsemantics > > https://www.datatorrent.com/blog/end-to-end-exactly-once-with-apache-apex/ > > > > HTH, > > Thomas > > > > > > On Thu, Oct 6, 2016 at 11:26 AM, Bandaru, Srinivas < > srinivas.band...@optum.com> wrote: > > Hi, Need some help! > > Need your advice in implementing the fault tolerance mechanism using > datatorrent. Currently we are trying to implement with EXACTLY_ONCE > scenario. > > We are referring the below documentation. The highlighted line says if we > need to use the EXACTLY_ONCE processing mode, the downstream operators > should have AT_MOST_ONCE. We added the operator level attributes in the > properties.xml (attached below) and when we launch the application, no > messages are coming through the last operator *topicUpdate *but we are > able to see the messages when we comment those attributes. > > *Please have a look at it, either we are specifying the attributes > incorrectly or is there any additional step to be done*. > > > > > > · *PROCESSING_MODE* > > static final Attribute > <https://www.datatorrent.com/docs/apidocs/com/datatorrent/api/Attribute.html><Operator.ProcessingMode > > <https://www.datatorrent.com/docs/apidocs/com/datatorrent/api/Operator.ProcessingMode.html>> > PROCESSING_MODE > > The payload processing mode for this operator - at most once, exactly > once, or default at least once. If the processing mode for an operator is > specified as AT_MOST_ONCE and no processing mode is specified for the > downstream operators if any, the processing mode of the downstream > operators is automatically set to AT_MOST_ONCE. If a different processing > mode is specified for the downstream operators it will result in an error. If > the processing mode for an operator is specified as EXACTLY_ONCE then the > processing mode for all downstream operators should be specified as > AT_MOST_ONCE otherwise it will result in an error. > > > > > > > > > > > > > > Thanks, > > Srinivas > > > This e-mail, including attachments, may include confidential and/or > proprietary information, and may be used only by the person or entity > to which it is addressed. If the reader of this e-mail is not the intended > recipient or his or her authorized agent, the reader is hereby notified > that any dissemination, distribution or copying of this e-mail is > prohibited. If you have received this e-mail in error, please notify the > sender by replying to this message and delete this e-mail immediately. > > > > > This e-mail, including attachments, may include confidential and/or > proprietary information, and may be used only by the person or entity > to which it is addressed. If the reader of this e-mail is not the intended > recipient or his or her authorized agent, the reader is hereby notified > that any dissemination, distribution or copying of this e-mail is > prohibited. If you have received this e-mail in error, please notify the > sender by replying to this message and delete this e-mail immediately. >
