I think I can answer my own question. delayed response will cause the
producer buffer to be full, which then result in either thread blocking or
message drop.
On Mon, Mar 16, 2015 at 11:24 PM, Steven Wu <stevenz...@gmail.com> wrote:
> please correct me if I am missing sth here. I am not understanding how
> would throttle work without cooperation/back-off from producer. new Java
> producer supports non-blocking API. why would delayed response be able to
> slow down producer? producer will continue to fire async sends.
>
> On Mon, Mar 16, 2015 at 10:58 PM, Guozhang Wang <wangg...@gmail.com>
> wrote:
>
>> I think we are really discussing two separate issues here:
>>
>> 1. Whether we should a) append-then-block-then-returnOKButThrottled or b)
>> block-then-returnFailDuetoThrottled for quota actions on produce requests.
>>
>> Both these approaches assume some kind of well-behaveness of the clients:
>> option a) assumes the client sets an proper timeout value while can just
>> ignore "OKButThrottled" response, while option b) assumes the client
>> handles the "FailDuetoThrottled" appropriately. For any malicious clients
>> that, for example, just keep retrying either intentionally or not, neither
>> of these approaches are actually effective.
>>
>> 2. For "OKButThrottled" and "FailDuetoThrottled" responses, shall we
>> encode
>> them as error codes or augment the protocol to use a separate field
>> indicating "status codes".
>>
>> Today we have already incorporated some status code as error codes in the
>> responses, e.g. ReplicaNotAvailable in MetadataResponse, the pros of this
>> is of course using a single field for response status like the HTTP status
>> codes, while the cons is that it requires clients to handle the error
>> codes
>> carefully.
>>
>> I think maybe we can actually extend the single-code approach to overcome
>> its drawbacks, that is, wrap the error codes semantics to the users so
>> that
>> users do not need to handle the codes one-by-one. More concretely,
>> following Jay's example the client could write sth. like this:
>>
>>
>> -----------------
>>
>> if(error.isOK())
>> // status code is good or the code can be simply ignored for this
>> request type, process the request
>> else if(error.needsRetry())
>> // throttled, transient error, etc: retry
>> else if(error.isFatal())
>> // non-retriable errors, etc: notify / terminate / other handling
>>
>> -----------------
>>
>> Only when the clients really want to handle, for example
>> FailDuetoThrottled
>> status code specifically, it needs to:
>>
>> if(error.isOK())
>> // status code is good or the code can be simply ignored for this
>> request type, process the request
>> else if(error == FailDuetoThrottled )
>> // throttled: log it
>> else if(error.needsRetry())
>> // transient error, etc: retry
>> else if(error.isFatal())
>> // non-retriable errors, etc: notify / terminate / other handling
>>
>> -----------------
>>
>> And for implementation we can probably group the codes accordingly like
>> HTTP status code such that we can do:
>>
>> boolean Error.isOK() {
>> return code < 300 && code >= 200;
>> }
>>
>> Guozhang
>>
>> On Mon, Mar 16, 2015 at 10:24 PM, Ewen Cheslack-Postava <
>> e...@confluent.io>
>> wrote:
>>
>> > Agreed that trying to shoehorn non-error codes into the error field is a
>> > bad idea. It makes it *way* too easy to write code that looks (and
>> should
>> > be) correct but is actually incorrect. If necessary, I think it's much
>> > better to to spend a couple of extra bytes to encode that information
>> > separately (a "status" or "warning" section of the response). An
>> indication
>> > that throttling is occurring is something I'd expect to be indicated by
>> a
>> > bit flag in the response rather than as an error code.
>> >
>> > Gwen - I think an error code makes sense when the request actually
>> failed.
>> > Option B, which Jun was advocating, would have appended the messages
>> > successfully. If the rate-limiting case you're talking about had
>> > successfully committed the messages, I would say that's also a bad use
>> of
>> > error codes.
>> >
>> >
>> > On Mon, Mar 16, 2015 at 10:16 PM, Gwen Shapira <gshap...@cloudera.com>
>> > wrote:
>> >
>> > > We discussed an error code for rate-limiting (which I think made
>> > > sense), isn't it a similar case?
>> > >
>> > > On Mon, Mar 16, 2015 at 10:10 PM, Jay Kreps <jay.kr...@gmail.com>
>> wrote:
>> > > > My concern is that as soon as you start encoding non-error response
>> > > > information into error codes the next question is what to do if two
>> > such
>> > > > codes apply (i.e. you have a replica down and the response is
>> > quota'd). I
>> > > > think I am trying to argue that error should mean "why we failed
>> your
>> > > > request", for which there will really only be one reason, and any
>> other
>> > > > useful information we want to send back is just another field in the
>> > > > response.
>> > > >
>> > > > -Jay
>> > > >
>> > > > On Mon, Mar 16, 2015 at 9:51 PM, Gwen Shapira <
>> gshap...@cloudera.com>
>> > > wrote:
>> > > >
>> > > >> I think its not too late to reserve a set of error codes (200-299?)
>> > > >> for "non-error" codes.
>> > > >>
>> > > >> It won't be backward compatible (i.e. clients that currently do
>> "else
>> > > >> throw" will throw on non-errors), but perhaps its worthwhile.
>> > > >>
>> > > >> On Mon, Mar 16, 2015 at 9:42 PM, Jay Kreps <jay.kr...@gmail.com>
>> > wrote:
>> > > >> > Hey Jun,
>> > > >> >
>> > > >> > I'd really really really like to avoid that. Having just spent a
>> > > bunch of
>> > > >> > time on the clients, using the error codes to encode other
>> > information
>> > > >> > about the response is super dangerous. The error handling is one
>> of
>> > > the
>> > > >> > hardest parts of the client (Guozhang chime in here).
>> > > >> >
>> > > >> > Generally the error handling looks like
>> > > >> > if(error == none)
>> > > >> > // good, process the request
>> > > >> > else if(error == KNOWN_ERROR_1)
>> > > >> > // handle known error 1
>> > > >> > else if(error == KNOWN_ERROR_2)
>> > > >> > // handle known error 2
>> > > >> > else
>> > > >> > throw Errors.forCode(error).exception(); // or some other
>> > default
>> > > >> > behavior
>> > > >> >
>> > > >> > This works because we have a convention that and error is
>> something
>> > > that
>> > > >> > prevented your getting the response so the default handling case
>> is
>> > > sane
>> > > >> > and forward compatible. It is tempting to use the error code to
>> > convey
>> > > >> > information in the success case. For example we could use error
>> > codes
>> > > to
>> > > >> > encode whether quotas were enforced, whether the request was
>> served
>> > > out
>> > > >> of
>> > > >> > cache, whether the stock market is up today, or whatever. The
>> > problem
>> > > is
>> > > >> > that since these are not errors as far as the client is
>> concerned it
>> > > >> should
>> > > >> > not throw an exception but process the response, but now we
>> created
>> > an
>> > > >> > explicit requirement that that error be handled explicitly since
>> it
>> > is
>> > > >> > different. I really think that this kind of information is not an
>> > > error,
>> > > >> it
>> > > >> > is just information, and if we want it in the response we should
>> do
>> > > the
>> > > >> > right thing and add a new field to the response.
>> > > >> >
>> > > >> > I think you saw the Samza bug that was literally an example of
>> this
>> > > >> > happening and leading to an infinite retry loop.
>> > > >> >
>> > > >> > Further more I really want to emphasize that hitting your quota
>> in
>> > the
>> > > >> > design that Adi has proposed is actually not an error condition
>> at
>> > > all.
>> > > >> It
>> > > >> > is totally reasonable in any bootstrap situation to intentionally
>> > > want to
>> > > >> > run at the limit the system imposes on you.
>> > > >> >
>> > > >> > -Jay
>> > > >> >
>> > > >> >
>> > > >> >
>> > > >> > On Mon, Mar 16, 2015 at 4:27 PM, Jun Rao <j...@confluent.io>
>> wrote:
>> > > >> >
>> > > >> >> It's probably useful for a client to know whether its requests
>> are
>> > > >> >> throttled or not (e.g., for monitoring and alerting). From that
>> > > >> >> perspective, option B (delay the requests and return an error)
>> > seems
>> > > >> >> better.
>> > > >> >>
>> > > >> >> Thanks,
>> > > >> >>
>> > > >> >> Jun
>> > > >> >>
>> > > >> >> On Wed, Mar 4, 2015 at 3:51 PM, Aditya Auradkar <
>> > > >> >> aaurad...@linkedin.com.invalid> wrote:
>> > > >> >>
>> > > >> >> > Posted a KIP for quotas in kafka.
>> > > >> >> >
>> > https://cwiki.apache.org/confluence/display/KAFKA/KIP-13+-+Quotas
>> > > >> >> >
>> > > >> >> > Appreciate any feedback.
>> > > >> >> >
>> > > >> >> > Aditya
>> > > >> >> >
>> > > >> >>
>> > > >>
>> > >
>> >
>> >
>> >
>> > --
>> > Thanks,
>> > Ewen
>> >
>>
>>
>>
>> --
>> -- Guozhang
>>
>
>
