What happens by default in absense of backpressure...

# rx

[dimsuz]

What happens by default in absense of backpressure support? For example here:

publishSubject.concatMap { Observable.delay(3000) }

If subject will very quickly emit a lot of items, what happens? Will they get buffered up to a certain point?
Or not at all? Can one expect that quickly emitting 3 items will be OK, but 1 000 000 items will throw MissingBackrpressure?
Where's that point when OK becomes an exception? :)

I tried searching javadoc for this info, but didn't succeed. If this is documented, please point me to the place in the docs.

[alexsullivan114]

Observable (and `Subject`s) will buffer forever until an OOM is hit. You should only receive a MissingBackpressureException when using a Flowable

[dimsuz]

I see! Thanks for clarification!

[ursus]

I might be making this up but there is some internal config for the buffer, its 256 or something

[gildor]

It’s only default buffer size ( I think it’s 128 values)

[alexsullivan114]

My understanding is that `Observable`s will just keep buffering forever...For Flowable I know there's some type of internal, fixed size buffer that can buffer some amount (maybe 128/256?) before it crashes

[ursus]

if you look at the sources, almost all operators have a buffer overload,

`

BUFFER_SIZE = Math.max(1, Integer.getInteger("rx2.buffer-size", 128));

`

[ursus]

I wonder what happens after that .. does it block? or throw?

[alexsullivan114]

That's interesting. I know there's some internal buffering with the observeOn operator to improve performance for bursty sources but I'm not sure about those internal buffers