Given a dart stream, how can I filter it so that there is maximum one value per minute?
Somthing like:
https://github.com/ReactiveX/RxJava/wiki/Filtering-Observables#throttlefirst
Background
I'm building a flutter app.
I use getPositionStream to get a stream of the location.
When I recieve a positionChange I update a GoogleMap.
However getPositionStream returns too many events, so I want to filter them to speed up the response.
EDIT
Note for #pskink comment
This should be emmiting max one location change each second?
getPositionStream(desiredAccuracy: LocationAccuracy.best).throttleTime(Duration(seconds: 1))
Related
I need to send a notification for a big amount of users.
I read about chunk(), cursor(), lazy() and lazyById() methods and I opted for the last one for retrieve the users.
I'd like to send the notification with a delay using $user->notify(...)->delay() every 100 users to avoid to process all the email at once.
How can achieve in an elegant way without using counters?
Is there any useful property I didn't find about the aforementioned methods?
Any suggestion will be appreciate :)
I'm lately trying to create a demo on real time streaming using NiFi -> Kafka -> Druid -> Superset. For the purposes of this demo I chose to use Wikipedia's RecentChanges API in order to get asynchronous data of the most recent changes.
I use this URL in order to get a response of changes. I'm calling the API constanlty in order to not miss any changes. This way I get a lot of duplicates that I do not want. Is there anyway to parameterize this API to fix it for example getting all the changes from the previous second and doing that everysecond or something else to tackle this issue. I'm trying to make a configuration for this uing NiFi, if someone has to add something on that part then visit this discussion on Cloudera.
Yes. See https://en.wikipedia.org/w/api.php?action=help&modules=query%2Brecentchanges Use rcstart and rcend to define your start and end times. You can use "now" for rcend.
I want to expand smartse's answer and come up with a solution. You want to put your API request in certain time windows, by shifting the start and end parameters. Windowing might work like this:
Initialize start, end timestamp parameters
Put those parameters as attributes on the flow
Downstream processors can call the API using those parameters
After doing that, you have to set start = previous_end + 1 second and end = now
When you determine the new window for the next run, you need the parameters from the previous run. This is why you have to remember those values. You can achieve this using NiFi's distributed map cache.
I've assembled a flow for you:
Zoom into Get next date range:
The end parameter is always now, so you just have to store the start parameter. FetchDistributedMapCache will fetch that for you and put it into stored.state attribute:
Set time range processor will initialize the parameters:
Notice that end is always now and start is either an initial date (for the first run) or the last end parameter plus 1 second. At this point the flow is directed into the Time range output, where you can call your API downstream. Additionally you have to update the stored.value. This happens in the ReplaceText processor:
Finally you update the state:
The lifecycle of the parameters are bound to the cache identifier. When you change the identifier, you start from scratch.
I mean like the meta event comes first , then channel event, then sysevent , meta event etc.
In the picture there is one meta event that comes, then channel event, and in between what if we will shuffle the order?
Most of these settings are independent, i.e., it does not matter in which order the events are processed.
However, some settings are affected by the current value of some other setting. For example, the program change events also uses the current values of the bank MSB/LSB controllers (this is not used in your file). Or the channel prefix (FF 20) meta event specifies the channel associated with the following meta or system exclusive events.
So if you don't know the meaning of an event, you should not reorder it.
I am trying to implement a method where a post(s) will be deleted after a given time frame. In my case 10 weeks.
How would I go about implementing a feature? I've read that Firebase does not support server-sided scripting. So how could I go about it? When users uploads a post, I do have a timestamp node attached. Is it a case of comparing the post's timestamp to a timestamp of 10 weeks? And then removing the post? Or is there another, more efficient way to achieve such a thing?
If I was to implement the aforementioned method, this would mean I'd require an observer/method to first analyse ALL posts, then do the comparison and then execute the second phase, depending on the timestamp - removeValue or simply return. And I wouldn't I need to use NotificatonCenter so I can call this code throughout my whole app?
Any input/advice would be appreciated.
My use-case is to identify entities from which expected events have not been received after X amount of time in real-time rather than using batch jobs. For Example:
If we have received PaymentInitiated event at time T but didn't receive either of PaymentFailed / PaymentAborted / PaymentSucedded by T+X, then raise a trigger saying PaymentStuck along with details of PaymentIntitiated event.
1. Can I capture such triggers using Esper?
In my actual use-case X is not constant and varies as per each record which I would know before the first event has occured.
2. Can Esper support registering such dynamic queries where X is not constant?
Thanks,
Harish
You could use a pattern such as "pattern [every pi=PaymentInitiated -> timer:interval(pi.amountOfTimeInSeconds) and not (PaymentAborted(id=pi.id) or PaymentStuck(id=p.id))]"
An outer join is also handy to detect absences. The solution patterns page in among the Esper web site has more examples.