Rewrite the reactive saveAll(Publisher<T>) methods in template and repository

[sothawo]

Currently the saveAll(Publisher) methods collect the publisher into a list, sending that to Elasticsearch as a batch request and then returning data from the response as Flux.

This needs to be changed to a more reactive approach, as it is not known how many items will be sent in with the publisher.

But we cannot simply just sent each element as a single index request, this would flood the network layer, so we need to

• buffer the incoming data into batches
• send this as a bulk request to Elasticsearch
• use backpressure handling with the upstream publisher to prevent flooding the transport client.
• provide the returned data in a continous flux.

I outlined the basic idea how this can be done in #2492

[patpatpat123]

Hello @sothawo ,

Many thanks for this PR.

We have several different test scenarios ready to save Flux sent at different rate (ranging from gentle to aggresive)

We would like to help test this PR.

However, we tried importing

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-elasticsearch</artifactId>
            <version>5.1.0-M3</version>
        </dependency>

And it seems we are not able to get your work.
Could you please suggest how can we get this merge please?

Will be glad to come back with some test results.

[sothawo]

Milestone 5.1.0-M3 is not yet released. You'll need to use the snapshot version 5.1.0-SNAPSHOT from the snapshot repository. Check the readme for the URL of this.

[patpatpat123]

Hello @sothawo,

With you advice, I was able to download the latest code.
I then run bunch of tests, ranging from gentle (10 messages per second) to something more aggressive (5000-8000 messages per second).

Only when it is aggressive, I am able to encounter this issue most of the time, after the program being run for a while:

reactor.core.publisher.Operators : Operator called default onErrorDropped
reactor.core.Exceptions$ErrorCallbackNotImplemented: reactor.core.Exceptions$OverflowException: Could not emit buffer due to lack of requests
Caused by: reactor.core.Exceptions$OverflowException: Could not emit buffer due to lack of requests
	at reactor.core.Exceptions.failWithOverflow(Exceptions.java:249)
	at reactor.core.publisher.FluxBufferTimeout$BufferTimeoutSubscriber.flushCallback(FluxBufferTimeout.java:227)
	at reactor.core.publisher.FluxBufferTimeout$BufferTimeoutSubscriber.lambda$new$0(FluxBufferTimeout.java:158)
	at io.micrometer.context.ContextSnapshot.lambda$wrap$0(ContextSnapshot.java:78)
	at reactor.core.scheduler.WorkerTask.call(WorkerTask.java:84)
	at reactor.core.scheduler.WorkerTask.call(WorkerTask.java:37)
	at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
	at java.base/java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:304)
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1136)
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635)
	at java.base/java.lang.Thread.run(Thread.java:833)

I am pasting the issue here first, since the only delta is this PR.

(I tried mongo, no problem, cassandra, no problem, elastic with new code but with low rate, no problem, elastic with new code but with high rate => issue)

If you believe it is not due to this change. please let me know.

[patpatpat123]

timeout.zip

[sothawo]

I don't know why you again bring up Mongo and cassandra, these are different projects with different drivers and connections.

Can you provide a runnable example that reproduces this? - and no, some setup which requires a Kafka is no reproducer for this.

5.1.0-M3 was released yesterday afternoon.