I am a novice in using the Esper event stream engine in Java.
I have two input stream one about States (device, state), and another about Measures (device, temperature)
It is possible to create a context to segment by device both streams?
I found an example in the documentation for you. It is at [1] and "4.2.2.1. Multiple Stream Definitions".
[1] http://esper.codehaus.org/esper-5.0.0/doc/reference/en-US/html_single/index.html#context_def_keyed
you also can create a window where you put only once the device.
for example
create window devicesDetail.std:unique(device) as (device string, temperature long, state string)
insert into devicesDetail select device, 0 as temperature, state from stream1
insert into devicesDetail select device, temperature, '' as state from stream2
and then you do a query into that window
select irstream from devicesDetail
Related
Here are two events:AppStartEvent and AppCrashEvent.
I need to count the number of two events over a period of time, and then to calculate the count(AppStartEvent)/count(AppCrashEvent).
My EPL is here
create context ctx4NestInCR
context ctx4Time initiated #now and pattern [every timer:interval(1 minute)] terminated after 15 minutes,
context ctx4AppName partition by appName from AppStartEvent, appName from AppCrashEvent
<------------------->
context ctx4NestInCR select count(s),count(c) from AppStartEvent as s, AppCrashEvent as c output last when terminated
And it does not work
Error starting statement: Joins require that at least one view is specified for each stream, no view was specified for s
Your post doesn't have the join? It only has the context and that wouldn't produce the message. I would suggest to correct the post.
You can also join streams by merging the two streams and treating them as one.
insert into AppEvent select 'crash' as condition from AppCrashEvent;
insert into AppEvent select 'start' as condition from AppStartEvent;
select count(condition='crash')/count(condition='start') from AppEvent;
I have a quite simple problem to modelize and I don't have experience in Esper, so I may be headed the wrong way so I'd like some insight.
Here's the scenario: I have one stream of events "ParkingEvent", with two types of events "SpotTaken" and "SpotFree". So I have an Esper context both partitioned by id and bordered by a starting event of type "SpotTaken" and an end event of type "SpotFree". The idea is to monitor a parking spot with a sensor and then aggregate data to count the number of times the spot has been taken and also the time occupation.
That's it, no time window or whatsoever, so it seems quite simple but I struggle aggregating data. Here's the code I got so far:
create context ParkingSpotOccupation
context PartionBySource
partition by source from SmartParkingEvent,
context ContextBorders
initiated by SmartParkingEvent(
type = "SpotTaken") as startEvent
terminated by SmartParkingEvent(
type = "SpotFree") as endEvent;
#Name("measurement_occupation")
context ParkingSpotOccupation
insert into CreateMeasurement
select
e.source as source,
"ParkingSpotOccupation" as type,
{
"startDate", min(e.time),
"endDate", max(e.time),
"duration", dateDifferenceInSec(max(e.time), min(e.time))
} as fragments
from
SmartParkingEvent e
output
snapshot when terminated;
I got the same data for min and max so I'm guessing I'm doing somthing wrong.
When I'm using context.ContextBorders.startEvent.time and context.ContextBorders.endEvent.time instead of min and max, the measurement_occupation statement is not triggered.
Given that measurements have already been computed by the EPL that you provided, this counts the number of times the spot has been taken (and freed) and totals up the duration:
select source, count(*), sum(duration) from CreateMeasurement group by source
I am looking for an EPL statement which fires an event each time a certain value has increased by a specified amount, with any number of events in between, for example:
Considering a stream, which continuously provides new prices.
I want to get a notification, e.g. if the price is greater than the first price + 100. Something like
select * from pattern[a=StockTick -> every b=StockTick(b.price>=a.price+100)];
But how to realize that I get the next event(s), if the increase is >= 200, >=300 and so forth?
Diverse tests with context and windows has not been successful so far, so I appreciate any help! Thanks!
The contexts would be the right way to go.
You could start by defining a start event like this:
create schema StartEvent(threshold int);
And then have context that uses the start event:
create context ThresholdContext inititiated by StartEvent as se
terminated after 5 years
context ThresholdContext select * from pattern[a=StockTick -> every b=StockTick(b.price>=context.se.threshold)];
You can generate the StartEvent using "insert into" from the same pattern (probably want to remove the "every") or have the listener send in a StartEvent or declare another pattern that fires just once for creating a StartEvent.
I am using esper and when I query my named window with timer:interval(10 sec) i get the same event duplicated after every 10 secs. I doesn't outputs other events present in the window.
here is the EPL
on pattern[every timer:interval(20 sec)] select DeviceIP, parent , child, Supress, Status from testZabbixProblem"
The engine outputs all rows in one call to the listener and delivering all rows at once as an array and not just one row.
I'm trying to generate a stream of deduplicated events without specifying any window policy beyond that used for the deduplication. Using an output first every clause on my queries appears to have the desired effect, but not when those queries are inserting directly into a stream.
For the example given below, say that I'm trying to detect only the first honk from each car in a 4-hour window.
(define-event-type! "CarEvent"
{:license_plate java.lang.String})
(define-event-type! "HonkEvent"
{:volume java.lang.Integer}
:supertypes #{"CarEvent"})
(define-variant! "HonkEventDeduplicated" "HonkEvent")
(define-statement! "context-IndividualCarContext"
"create context IndividualCarContext partition by license_plate from CarEvent")
(define-statement! "populate-HonkEventDeduplicated"
"context IndividualCarContext
insert into HonkEventDeduplicated
select * from HonkEvent
group by license_plate
output first every 4 hours")
However -- select * from HonkEventDeduplicated fires on every single honk event, even when the same car honks twice in a row.
Instead of using output first every clause filtering, this can be done with the std:firstunique view:
(define-statement!
"populate-HonkEventDeduplicated"
"insert into HonkEventDeduplicated
select * from HonkEvent.win:time(4 hours).std:firstunique(license_plate)")