I have an example where I want to use Flux.generate because I don't want to make the expensive blocking call unless / until a subscriber is asking for it. Specifically, I am calling Elasticsearch multiple times (effectively doing paging) until there are no more hits. I have implemented this using standard blocking calls in a Iterator<SearchResponse>. Where each call to the generate lambda blocks and the flux is then finished with .subscribeOn(Schedulers.boundedElastic()). However, I would like to use Spring's ReactiveElasticsearchClient that returns a Mono<SearchResponse> but still want to do it one at a time.
Here is the previous code using blocking:
public Iterator<SearchResponse> createDeepQueryIterator(@NonNull PITSearchInput input){
return new PointInTimeIterator(elasticClient, input);
}
public Flux<SearchResponse> createDeepQueryFlux(@NonNull PITSearchInput input){
return Flux.<SearchResponse, PointInTimeIterator>generate(
() -> new PointInTimeIterator(elasticClient, input),
(deepQueryIterator, sink) -> {
if (deepQueryIterator.hasNext()) {
sink.next(deepQueryIterator.next());
}else{
sink.complete();
}
return deepQueryIterator;
},
(deepQueryIterator) -> deepQueryIterator.shutdown())
.subscribeOn(Schedulers.boundedElastic());
}
The above works well in that it waits to make the next call to ES until a (the) subscriber is ready for the next block of data.
In the below I am trying to use Spring's ReactiveElasticsearchClient but the issue is that multiple calls are make to ES before subscriber has processed the first.
public Flux<SearchResponse> createDeepQuery(PointInTimeIteratorFactory.PITSearchInput input) {
log.info("Creating flux");
AtomicReference<PitId> pitId = new AtomicReference<>();
AtomicInteger count = new AtomicInteger();
Mono<PitId> pitIdMono =
Mono.fromCallable(
() -> {
pitId.set(createPIT(input));
return pitId.get();
})
.subscribeOn(Schedulers.boundedElastic());
Mono<SearchResponse> searchResponseMono =
pitIdMono.flatMap(
p -> {
log.info("Calling search");
return reactiveElasticsearchClient.searchForResponse(createSearchRequestFrom(p, input));
});
Flux<SearchResponse> expand =
searchResponseMono
.expand(
(searchResponse -> {
int hitCount = searchResponse.getHits().getHits().length;
count.addAndGet(hitCount);
log.info("Previous returned {} hits totaling {}", hitCount, count.get());
if (count.get() > input.getMaxTotalSize()
|| hitCount < input.getMaxSizePerQuery()){
log.info("Returning empty");
return Mono.empty();
}
log.info("Calling search");
pitId.set(new PitId(searchResponse.pointInTimeId()));
return reactiveElasticsearchClient.searchForResponse(
createSearchRequestFrom(searchResponse, input));
}))
.doFinally(
p -> {
deletePIT(pitId.get());
});
return expand;
}
So the question is not to use the reactive client's ability to return a Mono<SearchResponse> in a Flux but only doing so one-at-a-time as needed by the subscriber.
The below is the logging from the Flux -> Mono method above with the PitTest logging coming from the test onNext() of the flux.
2021-12-02 13:13:37.300 INFO 13704 --- [ main] a.a.t.ReactivePointInTimeIteratorFactory : Creating flux
2021-12-02 13:13:37.346 INFO 13704 --- [oundedElastic-1] a.a.t.ReactivePointInTimeIteratorFactory : Creating PIT
2021-12-02 13:13:37.407 INFO 13704 --- [oundedElastic-1] a.a.t.ReactivePointInTimeIteratorFactory : Calling search
2021-12-02 13:13:38.176 INFO 13704 --- [or-http-epoll-2] a.a.t.ReactivePointInTimeIteratorFactory : Previous returned 50 hits totaling 50
2021-12-02 13:13:38.177 INFO 13704 --- [or-http-epoll-2] a.a.t.ReactivePointInTimeIteratorFactory : Calling search
2021-12-02 13:13:38.177 INFO 13704 --- [or-http-epoll-2] a.a.t.ReactivePointInTimeIteratorFactory : Setting searchAfter to 1634877306267
2021-12-02 13:13:38.228 INFO 13704 --- [or-http-epoll-2] a.a.t.ReactivePointInTimeIteratorFactory : Previous returned 50 hits totaling 100
2021-12-02 13:13:38.228 INFO 13704 --- [or-http-epoll-2] a.a.t.ReactivePointInTimeIteratorFactory : Calling search
2021-12-02 13:13:38.228 INFO 13704 --- [or-http-epoll-2] a.a.t.ReactivePointInTimeIteratorFactory : Setting searchAfter to 1634877606162
2021-12-02 13:13:38.271 INFO 13704 --- [or-http-epoll-2] a.a.t.ReactivePointInTimeIteratorFactory : Previous returned 50 hits totaling 150
2021-12-02 13:13:38.271 INFO 13704 --- [or-http-epoll-2] a.a.t.ReactivePointInTimeIteratorFactory : Calling search
2021-12-02 13:13:38.272 INFO 13704 --- [or-http-epoll-2] a.a.t.ReactivePointInTimeIteratorFactory : Setting searchAfter to 1634877606362
2021-12-02 13:13:38.311 INFO 13704 --- [or-http-epoll-2] a.a.t.ReactivePointInTimeIteratorFactory : Previous returned 50 hits totaling 200
2021-12-02 13:13:38.312 INFO 13704 --- [or-http-epoll-2] a.a.t.ReactivePointInTimeIteratorFactory : Calling search
2021-12-02 13:13:38.312 INFO 13704 --- [or-http-epoll-2] a.a.t.ReactivePointInTimeIteratorFactory : Setting searchAfter to 1634877906244
2021-12-02 13:13:38.344 INFO 13704 --- [or-http-epoll-2] a.a.t.ReactivePointInTimeIteratorFactory : Previous returned 50 hits totaling 250
2021-12-02 13:13:38.345 INFO 13704 --- [or-http-epoll-2] a.a.t.ReactivePointInTimeIteratorFactory : Returning empty
2021-12-02 13:13:38.345 INFO 13704 --- [or-http-epoll-2] a.a.t.ReactivePointInTimeIteratorFactory : Closing PIT ReactivePointInTimeIteratorFactory.PitId(id=m_2xAwENYWN0aXZpdHlzdG9yZRZQQkRGWldmclI2cWZITEpoWDI1cGlRABZCZU8xbm55ZlFabXREYmNEdThESG1RAAAAAAAAWQcTFm5BcXdPU2xTUWE2bEU4dkVPVkpkWFEBFlBCREZaV2ZyUjZxZkhMSmhYMjVwaVEAAA==)
2021-12-02 13:13:40.171 INFO 13704 --- [ parallel-1] p.actss.activity.store.PitTest : [1634877306066]
2021-12-02 13:13:42.172 INFO 13704 --- [ parallel-2] p.actss.activity.store.PitTest : [1634877306272]
2021-12-02 13:13:44.172 INFO 13704 --- [ parallel-3] p.actss.activity.store.PitTest : [1634877606166]
2021-12-02 13:13:46.173 INFO 13704 --- [ parallel-4] p.actss.activity.store.PitTest : [1634877906057]
2021-12-02 13:13:48.174 INFO 13704 --- [ parallel-1] p.actss.activity.store.PitTest : [1634877906248]
2021-12-02 13:13:48.174 INFO 13704 --- [ parallel-1] p.actss.activity.store.PitTest : Complete
2021-12-02 13:13:48.174 INFO 13704 --- [ main] p.actss.activity.store.PitTest : blah
2021-12-02 13:13:48.175 INFO 13704 --- [ parallel-1] p.actss.activity.store.PitTest : onComplete
Update: Adding the PitTest code for completeness:
@Test
void testReactoiveFluxIt() throws InterruptedException {
Flux<SearchResponse> deepQuery = reactivePointInTimeIteratorFactory.createDeepQuery(...);
deepQuery
.delayElements(Duration.ofMillis(2000))
.doOnNext(p -> log.info(Arrays.toString(p.getHits().getHits()[0].getSortValues()))) //
.doOnComplete(() -> log.info("Complete")) //
.doFinally(p -> log.info(p.toString()))
.blockLast();
log.info("blah");
Thread.sleep(5000);
}
CodePudding user response：
delayElements switches to parallel scheduler and delays each emitted element by 2 seconds. This is why sort values are printed afterward.