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From Arvid Heise <ar...@ververica.com>
Subject Re: async io parallelism
Date Wed, 26 Feb 2020 14:41:11 GMT
Hi Alexey,

no there are as many instances as configured, but each would operate on the
current key group range and maintain the order on that.
So messages with the same key are never shuffled with ordered async.
Messages with different key would be processed potentially independently
and could change order.



On Mon, Feb 24, 2020 at 4:43 PM Alexey Trenikhun <yender@msn.com> wrote:

> Arvid, thank you.
> So there is single instance of FIFO per async IO operator regardless of
> parallelism of the async IO operator?
> Thanks,
> Alexey
> ------------------------------
> *From:* Arvid Heise <arvid@ververica.com>
> *Sent:* Saturday, February 22, 2020 1:23:01 PM
> *To:* Alexey Trenikhun <yender@msn.com>
> *Cc:* user@flink.apache.org <user@flink.apache.org>
> *Subject:* Re: async io parallelism
> Hi Alexey,
> the short answer is: order is preserved in all cases.
> Basically, ordered asyncIO maintains an internal FIFO queue where all
> pending elements reside. All async results are saved into this queue, but
> elements will only be outputted when the head element has a result.
> So assume you have three input records i1, i2, i3 and get the outputs
> asynchronously in the order o2, o1, o3 after 100 ms each, then there is no
> output after receiving o2, then o1 and o2 are outputted after 200 ms, and
> then o3 after 300 ms.
> Best,
> Arvid
> On Sat, Feb 22, 2020 at 2:22 AM Alexey Trenikhun <yender@msn.com> wrote:
> Hello,
> Let's say, my elements are simple key-value pairs, elements are coming
> from Kafka, where they were partitioned by "key", then I do processing
> using KeyedProcessFunction (keyed by same "key"), then I enrich elements
> using ordered RichAsyncFunction, then output to another
> KeyedProcessFunction (keyed by same "key") and then write to Kafka topic,
> again partitioned by same "key", something like this:
> FlinkKafkaConsumer -> keyBy("key") -> Intake(KeyedProcessFunction)
> -> AsyncDataStream.orderedWait() -> keyBy("key")->Output(
> KeyedProcessFunction)->FlinkKafkaProducer
> Will it preserve order of events with same "key"?
>    - Will Output function receive elements with same "key" in same order
>    as they were originally in Kafka?
>    - Will FlinkKafkaProducer writes elements with same "key" in same
>    order as they were originally in Kafka?
>    - Does it depend on parallelism of async IO? Documentation says "the
>    stream order is preserved", but if there are multiple parallel instances of
>    async function, does it mean order relative to each single instance? Or
>    total stream order?
> Thanks,
> Alexey

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