[ https://issues.apache.org/jira/browse/BEAM-2535?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16067342#comment-16067342 ]
Kenneth Knowles edited comment on BEAM-2535 at 6/29/17 8:45 PM: ---------------------------------------------------------------- CC [~reuvenlax] [~aljoscha] [~lzljs3620320] [~jkff] was (Author: kenn): CC [~reuvenlax] [~aljoscha] [~lzljs3620320] > Allow explicit output time independent of firing specification for all timers > ----------------------------------------------------------------------------- > > Key: BEAM-2535 > URL: https://issues.apache.org/jira/browse/BEAM-2535 > Project: Beam > Issue Type: New Feature > Components: beam-model, sdk-java-core > Reporter: Kenneth Knowles > Assignee: Kenneth Knowles > > Today, we have insufficient control over the event time timestamp of elements > output from a timer callback. > 1. For an event time timer, it is the timestamp of the timer itself. > 2. For a processing time timer, it is the current input watermark at the time > of processing. > But for both of these, we may want to reserve the right to output a > particular time, aka set a "watermark hold". > A naive implementation of a {{TimerWithWatermarkHold}} would work for making > sure output is not droppable, but does not fully explain window expiration > and late data/timer dropping. > In the natural interpretation of a timer as a feedback loop on a transform, > timers should be viewed as another channel of input, with a watermark, and > items on that channel _all need event time timestamps even if they are > delivered according to a different time domain_. > I propose that the specification for when a timer should fire should be > separated (with nice defaults) from the specification of the event time of > resulting outputs. These timestamps will determine a side channel with a new > "timer watermark" that constrains the output watermark. > - We still need to fire event time timers according to the input watermark, > so that event time timers fire. > - Late data dropping and window expiration will be in terms of the minimum > of the input watermark and the timer watermark. In this way, whenever a timer > is set, the window is not going to be garbage collected. > - We will need to make sure we have a way to "wake up" a window once it is > expired; this may be as simple as exhausting the timer channel as soon as the > input watermark indicates expiration of a window -- This message was sent by Atlassian JIRA (v6.4.14#64029)