[ https://issues.apache.org/jira/browse/BEAM-1283?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Kenneth Knowles updated BEAM-1283: ---------------------------------- Labels: backward-incompatible (was: ) > DoFn.Context.output spec for startBundle/finishBundle is a mess > --------------------------------------------------------------- > > Key: BEAM-1283 > URL: https://issues.apache.org/jira/browse/BEAM-1283 > Project: Beam > Issue Type: Bug > Components: beam-model, sdk-java-core > Reporter: Kenneth Knowles > Assignee: Kenneth Knowles > Labels: backward-incompatible > > The spec is here in Javadoc: > https://github.com/apache/beam/blob/master/sdks/java/core/src/main/java/org/apache/beam/sdk/transforms/DoFn.java#L128 > "If invoked from {{@StartBundle}} or {{@FinishBundle}}, this will attempt to > use the {{WindowFn}} of the input {{PCollection}} to determine what windows > the element should be in, throwing an exception if the {{WindowFn}} attempts > to access any information about the input element. The output element will > have a timestamp of negative infinity." > This is a collection of caveats that make this method not always technically > wrong, but quite a mess. Ideas that reasonable folks have suggested lately: > - The {{WindowFn}} cannot actually be applied because {{WindowFn}} is > allowed to see the element type. The spec just avoids this by limiting which > {{WindowFn}} can be used. > - There is no natural output timestamp, so it should always be provided. The > spec avoids this by specifying an arbitrary and fairly useless timestamp. > - If it is a merging {{WindowFn}} like sessions that has already been merged > then you'll just have a bogus proto window regardless of explicit timestamp > or not. > The use cases for these methods are best addressed by state plus window > expiry callback, so we should revisit this spec and probably just wipe it. -- This message was sent by Atlassian JIRA (v6.3.4#6332)