I agree DELAY or MEMORY is a well defined concept in other areas such as digital electronics, VLSI, Digital Signal Processing.
On Thu, Sep 17, 2015 at 3:39 PM, Chetan Narsude <che...@datatorrent.com> wrote: > Iteration implies that something is looping over. Whereas that's just one > use case of this functionality. One can take the output of an upstream > operator and give it to input of the downstream operator. > > AFAIK, DELAY is very well understood concept in event processing and > analogous to how we intend to use it. > > > On Wed, Sep 16, 2015 at 5:32 PM, David Yan <da...@datatorrent.com> wrote: > > > I think keeping the word ITERATION is clearer to the users because that's > > what it is for. > > The user wouldn't think he/she is trying to "delay" something... > > In any case, I am fine either way :) > > > > David > > > > On Wed, Sep 16, 2015 at 5:12 PM, Munagala Ramanath <r...@datatorrent.com> > > wrote: > > > > > I like ITERATION_WINDOW_OFFSET. > > > > > > Ram > > > > > > On Wed, Sep 16, 2015 at 4:42 PM, David Yan <da...@datatorrent.com> > > wrote: > > > > > > > Thanks Chetan. > > > > > > > > Can you point me to the location of Deduper code that may be helpful > > with > > > > the recovery implementation? > > > > > > > > Does anyone have any opinion on the renaming of > ITERATION_WINDOW_COUNT? > > > > DELAY_BY_WINDOW_COUNT? DELAY_WINDOW_COUNT? > > > > > > > > David > > > > > > > > On Wed, Sep 16, 2015 at 2:21 PM, Chetan Narsude < > > che...@datatorrent.com> > > > > wrote: > > > > > > > > > David, > > > > > > > > > > I have 3 comments: > > > > > > > > > > 1. The "ahead window" phrase you discussed above is really behind > > > window. > > > > > With Apex, the windows which are ahead are the windows with smaller > > > > window > > > > > Id. smaller window ids are followed by bigger window ids. > > > > > > > > > > 2. ITERATION_WINDOW_COUNT sounds like a misnomer. IMO, It should > be > > > > > something akin to DELAY_BY_WINDOW_COUNT as you are delaying the > > events > > > by > > > > > those many windows. You are not iterating over them as many times. > It > > > > also > > > > > resonates with PortContext.SLIDE_BY_WINDOW_COUNT > > > > > > > > > > 3. Deduper has similar requirement where large amount of data > > > > (potentially > > > > > even larger) needs to be partitioned. You can borrow the idea/code > > from > > > > > there. And perhaps abstract the code to be reusable. > > > > > > > > > > HTH. > > > > > > > > > > -- > > > > > Chetan > > > > > > > > > > On Wed, Sep 16, 2015 at 1:44 PM, David Yan <da...@datatorrent.com> > > > > wrote: > > > > > > > > > > > Hi all, > > > > > > > > > > > > One current disadvantage of Apex is the inability to do > iterations > > > and > > > > > > machine learning algorithms because we don't allow loops in the > > > > > application > > > > > > DAG (hence the name DAG). I am proposing that we allow loops in > > the > > > > DAG > > > > > if > > > > > > the loop advances the window ID by a configured amount. A JIRA > > > ticket > > > > > has > > > > > > been created: > > > > > > > > > > > > https://malhar.atlassian.net/browse/APEX-60 > > > > > > > > > > > > I have started this work in my fork at > > > > > > https://github.com/davidyan74/incubator-apex-core/tree/APEX-60. > > > > > > > > > > > > The current progress is that a simple test case works. Major > work > > > > still > > > > > > needs to be done with respect to recovery and partitioning. > > > > > > > > > > > > The value ITERATION_WINDOW_COUNT is an attribute to an input port > > of > > > an > > > > > > operator. If the value of the attribute is greater than or equal > > to > > > 1, > > > > > any > > > > > > tuples sent to the input port are treated to be > > > ITERATION_WINDOW_COUNT > > > > > > windows ahead of what they are. > > > > > > > > > > > > For recovery, we will need to checkpoint all the tuples between > > ports > > > > > with > > > > > > the to replay the looped tuples. During the recovery, if the > > > operator > > > > > has > > > > > > an input port, with ITERATION_WINDOW_COUNT=2, is recovering from > > > > > checkpoint > > > > > > window 14, the tuples for that input port from window 13 and > window > > > 14 > > > > > need > > > > > > to be replayed to be treated as window 15 and window 16 > > respectively > > > > > (13+2 > > > > > > and 14+2). > > > > > > > > > > > > In other words, we need to store all the tuples from window with > ID > > > > > > committedWindowId minus ITERATION_WINDOW_COUNT for recovery and > > purge > > > > the > > > > > > tuples earlier than that window. > > > > > > We can optimize this by only storing the tuples for > > > > > ITERATION_WINDOW_COUNT > > > > > > windows prior to any checkpoint. > > > > > > > > > > > > For that, we need a storage mechanism for the tuples. Chandni > > > already > > > > > has > > > > > > something that fits this usage case in Apex Malhar. The class is > > > > > > IdempotentStorageManager. In order for this to be used in Apex > > core, > > > > we > > > > > > need to deprecate the class in Apex Malhar and move it to Apex > > Core. > > > > > > > > > > > > A JIRA ticket has been created for this particular work: > > > > > > > > > > > > https://malhar.atlassian.net/browse/APEX-128 > > > > > > > > > > > > Some of the above has been discussed among Thomas, Chetan, > Chandni, > > > and > > > > > > myself. > > > > > > > > > > > > For partitioning, we have not started any discussion or > > > brainstorming. > > > > > We > > > > > > appreciate any feedback on this and any other aspect related to > > > > > supporting > > > > > > iterations in general. > > > > > > > > > > > > Thanks! > > > > > > > > > > > > David > > > > > > > > > > > > > > > > > > > > >
