Mickael, I had based the comment on KIP-72 description where brokers were muting all client channels once memory pool was empty. Having reviewed the PR today, I think it may be fine to delay muting and allocate small buffers outside of the pool. I would still not want to have a config parameter to decide what "small" means, a well chosen hard limit would suffice.
On Wed, Jan 11, 2017 at 3:05 PM, Mickael Maison <mickael.mai...@gmail.com> wrote: > Rajini, > > Why do you think we don't want to do the same for brokers ? > It feels like brokers would be affected the same way and could end up > delaying group/hearbeat requests. > > Also given queued.max.requests it seems unlikely that small requests > (<<1Kb) being allocated outside of the memory pool would cause OOM > exceptions > > > On Wed, Dec 14, 2016 at 12:29 PM, Rajini Sivaram <rsiva...@pivotal.io> > wrote: > > Edo, > > > > I wouldn't introduce a new config entry, especially since you don't need > it > > after KAFKA-4137. As a temporary measure that would work for consumers. > But > > you probably don't want to do the same for brokers - will be worth > checking > > with Radai since the implementation will be based on KIP-72. To do this > > only for consumers, you will need some conditions in the common network > > code while allocating and releasing buffers. A bit messy, but doable. > > > > > > > > On Wed, Dec 14, 2016 at 11:32 AM, Edoardo Comar <eco...@uk.ibm.com> > wrote: > > > >> Thanks Rajini, > >> Before Kafka-4137, we could avoid coordinator starvation without making > a > >> special case for a special connection, > >> but rather simply, in applying the buffer.memory check only to 'large' > >> responses > >> (e.g. size > 1k, possibly introducing a new config entry) in > >> > >> NetworkReceive.readFromReadableChannel(ReadableByteChannel) > >> > >> Essentially this would limit reading fetch responses but allow for other > >> responses to be processed. > >> > >> This is a sample of sizes for responses I collected : > >> > >> ***** size=108 APIKEY=3 METADATA > >> ***** size=28 APIKEY=10 GROUP_COORDINATOR > >> ***** size=193 APIKEY=11 JOIN_GROUP > >> ***** size=39 APIKEY=14 SYNC_GROUP > >> ***** size=39 APIKEY=9 OFFSET_FETCH > >> ***** size=45 APIKEY=2 LIST_OFFSETS > >> ***** size=88926 APIKEY=1 FETCH > >> ***** size=45 APIKEY=1 FETCH > >> ***** size=6 APIKEY=12 HEARTBEAT > >> ***** size=45 APIKEY=1 FETCH > >> ***** size=45 APIKEY=1 FETCH > >> ***** size=45 APIKEY=1 FETCH > >> ***** size=6 APIKEY=12 HEARTBEAT > >> ***** size=45 APIKEY=1 FETCH > >> ***** size=45 APIKEY=1 FETCH > >> > >> What do you think? > >> -------------------------------------------------- > >> Edoardo Comar > >> IBM MessageHub > >> eco...@uk.ibm.com > >> IBM UK Ltd, Hursley Park, SO21 2JN > >> > >> IBM United Kingdom Limited Registered in England and Wales with number > >> 741598 Registered office: PO Box 41, North Harbour, Portsmouth, Hants. > PO6 > >> 3AU > >> > >> > >> > >> From: Rajini Sivaram <rajinisiva...@googlemail.com> > >> To: dev@kafka.apache.org > >> Date: 13/12/2016 17:27 > >> Subject: Re: [DISCUSS] KIP-81: Max in-flight fetches > >> > >> > >> > >> Coordinator starvation: For an implementation based on KIP-72, there > will > >> be coordinator starvation without KAFKA-4137 since you would stop > reading > >> from sockets when the memory pool is full (the fact that coordinator > >> messages are small doesn't help). I imagine you can work around this by > >> treating coordinator connections as special connections but that spills > >> over to common network code. Separate NetworkClient for coordinator > >> proposed in KAFKA-4137 would be much better. > >> > >> On Tue, Dec 13, 2016 at 3:47 PM, Mickael Maison < > mickael.mai...@gmail.com> > >> wrote: > >> > >> > Thanks for all the feedback. > >> > > >> > I've updated the KIP with all the details. > >> > Below are a few of the main points: > >> > > >> > - Overall memory usage of the consumer: > >> > I made it clear the memory pool is only used to store the raw bytes > >> > from the network and that the decompressed/deserialized messages are > >> > not stored in it but as extra memory on the heap. In addition, the > >> > consumer also keeps track of other things (in flight requests, > >> > subscriptions, etc..) that account for extra memory as well. So this > >> > is not a hard bound memory constraint but should still allow to > >> > roughly size how much memory can be used. > >> > > >> > - Relation with the existing settings: > >> > There are already 2 settings that deal with memory usage of the > >> > consumer. I suggest we lower the priority of > >> > `max.partition.fetch.bytes` (I wonder if we should attempt to > >> > deprecate it or increase its default value so it's a contraint less > >> > likely to be hit) and have the new setting `buffer.memory` as High. > >> > I'm a bit unsure what's the best default value for `buffer.memory`, I > >> > suggested 100MB in the KIP (2 x `fetch.max.bytes`), but I'd appreciate > >> > feedback. It should always at least be equal to `max.fetch.bytes`. > >> > > >> > - Configuration name `buffer.memory`: > >> > I think it's the name that makes the most sense. It's aligned with the > >> > producer and as mentioned generic enough to allow future changes if > >> > needed. > >> > > >> > - Coordination starvation: > >> > Yes this is a potential issue. I'd expect these requests to be small > >> > enough to not be affected too much. If that's the case KAFKA-4137 > >> > suggests a possible fix. > >> > > >> > > >> > > >> > On Tue, Dec 13, 2016 at 9:31 AM, Ismael Juma <ism...@juma.me.uk> > wrote: > >> > > Makes sense Jay. > >> > > > >> > > Mickael, in addition to how we can compute defaults of the other > >> settings > >> > > from `buffer.memory`, it would be good to specify what is allowed > and > >> how > >> > > we handle the different cases (e.g. what do we do if > >> > > `max.partition.fetch.bytes` > >> > > is greater than `buffer.memory`, is that simply not allowed?). > >> > > > >> > > To summarise the gap between the ideal scenario (user specifies how > >> much > >> > > memory the consumer can use) and what is being proposed: > >> > > > >> > > 1. We will decompress and deserialize the data for one or more > >> partitions > >> > > in order to return them to the user and we don't account for the > >> > increased > >> > > memory usage resulting from that. This is likely to be significant > on > >> a > >> > per > >> > > record basis, but we try to do it for the minimal number of records > >> > > possible within the constraints of the system. Currently the > >> constraints > >> > > are: we decompress and deserialize the data for a partition at a > time > >> > > (default `max.partition.fetch.bytes` is 1MB, but this is a soft > limit > >> in > >> > > case there are oversized messages) until we have enough records to > >> > > satisfy `max.poll.records` > >> > > (default 500) or there are no more completed fetches. It seems like > >> this > >> > > may be OK for a lot of cases, but some tuning will still be required > >> in > >> > > others. > >> > > > >> > > 2. We don't account for bookkeeping data structures or intermediate > >> > objects > >> > > allocated during the general operation of the consumer. Probably > >> > something > >> > > we have to live with as the cost/benefit of fixing this doesn't seem > >> > worth > >> > > it. > >> > > > >> > > Ismael > >> > > > >> > > On Tue, Dec 13, 2016 at 8:34 AM, Jay Kreps <j...@confluent.io> > wrote: > >> > > > >> > >> Hey Ismael, > >> > >> > >> > >> Yeah I think we are both saying the same thing---removing only > works > >> if > >> > you > >> > >> have a truly optimal strategy. Actually even dynamically computing > a > >> > >> reasonable default isn't totally obvious (do you set > fetch.max.bytes > >> to > >> > >> equal buffer.memory to try to queue up as much data in the network > >> > buffers? > >> > >> Do you try to limit it to your socket.receive.buffer size so that > you > >> > can > >> > >> read it in a single shot?). > >> > >> > >> > >> Regarding what is being measured, my interpretation was the same as > >> > yours. > >> > >> I was just adding to the previous point that buffer.memory setting > >> would > >> > >> not be a very close proxy for memory usage. Someone was pointing > out > >> > that > >> > >> compression would make this true, and I was just adding that even > >> > without > >> > >> compression the object overhead would lead to a high expansion > >> factor. > >> > >> > >> > >> -Jay > >> > >> > >> > >> On Mon, Dec 12, 2016 at 11:53 PM, Ismael Juma <ism...@juma.me.uk> > >> > wrote: > >> > >> > >> > >> > Hi Jay, > >> > >> > > >> > >> > About `max.partition.fetch.bytes`, yes it was an oversight not to > >> > lower > >> > >> its > >> > >> > priority as part of KIP-74 given the existence of > `fetch.max.bytes` > >> > and > >> > >> the > >> > >> > fact that we can now make progress in the presence of oversized > >> > messages > >> > >> > independently of either of those settings. > >> > >> > > >> > >> > I agree that we should try to set those values automatically > based > >> on > >> > >> > `buffer.memory`, but I am not sure if we can have a truly optimal > >> > >> strategy. > >> > >> > So, I'd go with reducing the priority to "low" instead of > removing > >> > >> > `fetch.max.bytes` and `max.partition.fetch.bytes` altogether for > >> now. > >> > If > >> > >> > experience in the field tells us that the auto strategy is good > >> > enough, > >> > >> we > >> > >> > can consider removing them (yes, I know, it's unlikely to happen > as > >> > there > >> > >> > won't be that much motivation then). > >> > >> > > >> > >> > Regarding the "conversion from packed bytes to java objects" > >> comment, > >> > >> that > >> > >> > raises the question: what are we actually measuring here? From > the > >> > KIP, > >> > >> > it's not too clear. My interpretation was that we were not > >> measuring > >> > the > >> > >> > memory usage of the Java objects. In that case, `buffer.memory` > >> seems > >> > >> like > >> > >> > a reasonable name although perhaps the user's expectation is that > >> we > >> > >> would > >> > >> > measure the memory usage of the Java objects? > >> > >> > > >> > >> > Ismael > >> > >> > > >> > >> > On Tue, Dec 13, 2016 at 6:21 AM, Jay Kreps <j...@confluent.io> > >> wrote: > >> > >> > > >> > >> > > I think the question is whether we have a truly optimal > strategy > >> for > >> > >> > > deriving the partition- and fetch-level configs from the global > >> > >> setting. > >> > >> > If > >> > >> > > we do then we should just get rid of them. If not, then if we > can > >> at > >> > >> > least > >> > >> > > derive usually good and never terrible settings from the global > >> > limit > >> > >> at > >> > >> > > initialization time maybe we can set them automatically unless > >> the > >> > user > >> > >> > > overrides with an explicit conifg. Even the latter would let us > >> > mark it > >> > >> > low > >> > >> > > priority which at least takes it off the list of things you > have > >> to > >> > >> grok > >> > >> > to > >> > >> > > use the consumer which I suspect would be much appreciated by > our > >> > poor > >> > >> > > users. > >> > >> > > > >> > >> > > Regardless it'd be nice to make sure we get an explanation of > the > >> > >> > > relationships between the remaining memory configs in the KIP > and > >> in > >> > >> the > >> > >> > > docs. > >> > >> > > > >> > >> > > I agree that buffer.memory isn't bad. > >> > >> > > > >> > >> > > -Jay > >> > >> > > > >> > >> > > > >> > >> > > On Mon, Dec 12, 2016 at 2:56 PM, Jason Gustafson < > >> > ja...@confluent.io> > >> > >> > > wrote: > >> > >> > > > >> > >> > > > Yeah, that's a good point. Perhaps in retrospect, it would > have > >> > been > >> > >> > > better > >> > >> > > > to define `buffer.memory` first and let `fetch.max.bytes` be > >> based > >> > >> off > >> > >> > of > >> > >> > > > it. I like `buffer.memory` since it gives the consumer nice > >> > symmetry > >> > >> > with > >> > >> > > > the producer and its generic naming gives us some flexibility > >> > >> > internally > >> > >> > > > with how we use it. We could still do that I guess, if we're > >> > willing > >> > >> to > >> > >> > > > deprecate `fetch.max.bytes` (one release after adding it!). > >> > >> > > > > >> > >> > > > As for `max.partition.fetch.bytes`, it's noted in KIP-74 that > >> it > >> > is > >> > >> > still > >> > >> > > > useful in Kafka Streams, but I agree it makes sense to lower > >> its > >> > >> > priority > >> > >> > > > in favor of `fetch.max.bytes`. > >> > >> > > > > >> > >> > > > -Jason > >> > >> > > > > >> > >> > > > On Sat, Dec 10, 2016 at 2:27 PM, Jay Kreps <j...@confluent.io > > > >> > wrote: > >> > >> > > > > >> > >> > > > > Jason, it's not just decompression but also the conversion > >> from > >> > >> > packed > >> > >> > > > > bytes to java objects, right? That can be even larger than > >> the > >> > >> > > > > decompression blow up. I think this may be okay, the > problem > >> may > >> > >> just > >> > >> > > be > >> > >> > > > > that the naming is a bit misleading. In the producer you > are > >> > >> > literally > >> > >> > > > > allocating a buffer of that size, so the name buffer.memory > >> > makes > >> > >> > > sense. > >> > >> > > > In > >> > >> > > > > this case it is something more like > >> max.bytes.read.per.poll.call > >> > >> > > > (terrible > >> > >> > > > > name, but maybe something like that?). > >> > >> > > > > > >> > >> > > > > Mickael, I'd second Jason's request for the default and > >> expand > >> > on > >> > >> it. > >> > >> > > We > >> > >> > > > > currently have several consumer-related memory > >> > >> > > > > settings--max.partition.fetch.bytes, fetch.max.bytes. I > don't > >> > >> think > >> > >> > it > >> > >> > > > is > >> > >> > > > > clear today how to set these. For example we mark > >> > >> > > > max.partition.fetch.bytes > >> > >> > > > > as high importance and fetch.max.bytes as medium, but it > >> seems > >> > like > >> > >> > it > >> > >> > > > > would be the other way around. Can we think this through > from > >> > the > >> > >> > point > >> > >> > > > of > >> > >> > > > > view of a lazy user? I.e. I have 64MB of space to use for > my > >> > >> > consumer, > >> > >> > > in > >> > >> > > > > an ideal world I'd say, "hey consumer here is 64MB go use > >> that > >> > as > >> > >> > > > > efficiently as possible" and not have to tune a bunch of > >> > individual > >> > >> > > > things > >> > >> > > > > with complex relationships. Maybe one or both of the > existing > >> > >> > settings > >> > >> > > > can > >> > >> > > > > either be eliminated or at the least marked as low priority > >> and > >> > we > >> > >> > can > >> > >> > > > > infer a reasonable default from the new config your > >> introducing? > >> > >> > > > > > >> > >> > > > > -jay > >> > >> > > > > > >> > >> > > > > On Fri, Dec 9, 2016 at 2:08 PM, Jason Gustafson < > >> > >> ja...@confluent.io> > >> > >> > > > > wrote: > >> > >> > > > > > >> > >> > > > > > Hi Mickael, > >> > >> > > > > > > >> > >> > > > > > I think the approach looks good, just a few minor > >> questions: > >> > >> > > > > > > >> > >> > > > > > 1. The KIP doesn't say what the default value of > >> > `buffer.memory` > >> > >> > will > >> > >> > > > be. > >> > >> > > > > > Looks like we use 50MB as the default for > >> `fetch.max.bytes`, > >> > so > >> > >> > > perhaps > >> > >> > > > > it > >> > >> > > > > > makes sense to set the default based on that. Might also > be > >> > worth > >> > >> > > > > > mentioning somewhere the constraint between the two > >> configs. > >> > >> > > > > > 2. To clarify, this limit only affects the uncompressed > >> size > >> > of > >> > >> the > >> > >> > > > > fetched > >> > >> > > > > > data, right? The consumer may still exceed it in order to > >> > store > >> > >> the > >> > >> > > > > > decompressed record data. We delay decompression until > the > >> > >> records > >> > >> > > are > >> > >> > > > > > returned to the user, but because of max.poll.records, we > >> may > >> > end > >> > >> > up > >> > >> > > > > > holding onto the decompressed data from a single > partition > >> > for a > >> > >> > few > >> > >> > > > > > iterations. I think this is fine, but probably worth > noting > >> in > >> > >> the > >> > >> > > KIP. > >> > >> > > > > > 3. Is there any risk using the MemoryPool that, after we > >> fill > >> > up > >> > >> > the > >> > >> > > > > memory > >> > >> > > > > > with fetch data, we can starve the coordinator's > >> connection? > >> > >> > Suppose, > >> > >> > > > for > >> > >> > > > > > example, that we send a bunch of pre-fetches right before > >> > >> returning > >> > >> > > to > >> > >> > > > > the > >> > >> > > > > > user. These fetches might return before the next call to > >> > poll(), > >> > >> in > >> > >> > > > which > >> > >> > > > > > case we might not have enough memory to receive > heartbeats, > >> > which > >> > >> > > would > >> > >> > > > > > block us from sending additional heartbeats until the > next > >> > call > >> > >> to > >> > >> > > > > poll(). > >> > >> > > > > > Not sure it's a big problem since heartbeats are tiny, > but > >> > might > >> > >> be > >> > >> > > > worth > >> > >> > > > > > thinking about. > >> > >> > > > > > > >> > >> > > > > > Thanks, > >> > >> > > > > > Jason > >> > >> > > > > > > >> > >> > > > > > > >> > >> > > > > > On Fri, Dec 2, 2016 at 4:31 AM, Mickael Maison < > >> > >> > > > mickael.mai...@gmail.com > >> > >> > > > > > > >> > >> > > > > > wrote: > >> > >> > > > > > > >> > >> > > > > > > It's been a few days since the last comments. KIP-72 > vote > >> > seems > >> > >> > to > >> > >> > > > > > > have passed so if I don't get any new comments I'll > start > >> > the > >> > >> > vote > >> > >> > > on > >> > >> > > > > > > Monday. > >> > >> > > > > > > Thanks > >> > >> > > > > > > > >> > >> > > > > > > On Mon, Nov 14, 2016 at 6:25 PM, radai < > >> > >> > radai.rosenbl...@gmail.com > >> > >> > > > > >> > >> > > > > > wrote: > >> > >> > > > > > > > +1 - there's is a need for an effective way to > control > >> > kafka > >> > >> > > memory > >> > >> > > > > > > > consumption - both on the broker and on clients. > >> > >> > > > > > > > i think we could even reuse the exact same param > name - > >> > >> > > > > > > *queued.max.bytes *- > >> > >> > > > > > > > as it would serve the exact same purpose. > >> > >> > > > > > > > > >> > >> > > > > > > > also (and again its the same across the broker and > >> > clients) > >> > >> > this > >> > >> > > > > bound > >> > >> > > > > > > > should also cover decompression, at some point. > >> > >> > > > > > > > the problem with that is that to the best of my > >> knowledge > >> > the > >> > >> > > > current > >> > >> > > > > > > wire > >> > >> > > > > > > > protocol does not declare the final, uncompressed > size > >> of > >> > >> > > anything > >> > >> > > > up > >> > >> > > > > > > front > >> > >> > > > > > > > - all we know is the size of the compressed buffer. > >> this > >> > may > >> > >> > > > require > >> > >> > > > > a > >> > >> > > > > > > > format change in the future to properly support? > >> > >> > > > > > > > > >> > >> > > > > > > > On Mon, Nov 14, 2016 at 10:03 AM, Mickael Maison < > >> > >> > > > > > > mickael.mai...@gmail.com> > >> > >> > > > > > > > wrote: > >> > >> > > > > > > > > >> > >> > > > > > > >> Thanks for all the replies. > >> > >> > > > > > > >> > >> > >> > > > > > > >> I've updated the KIP: > >> > >> > > > > > > >> https://cwiki.apache.org/ > confluence/display/KAFKA/KIP- > >> > >> > > > > > > >> 81%3A+Bound+Fetch+memory+usage+in+the+consumer > >> > >> > > > > > > >> The main point is to selectively read from sockets > >> > instead > >> > >> of > >> > >> > > > > > > >> throttling FetchRequests sends. I also mentioned it > >> will > >> > be > >> > >> > > > reusing > >> > >> > > > > > > >> the MemoryPool implementation created in KIP-72 > >> instead > >> > of > >> > >> > > adding > >> > >> > > > > > > >> another memory tracking method. > >> > >> > > > > > > >> > >> > >> > > > > > > >> Please have another look. As always, comments are > >> > welcome ! > >> > >> > > > > > > >> > >> > >> > > > > > > >> On Thu, Nov 10, 2016 at 2:47 AM, radai < > >> > >> > > > radai.rosenbl...@gmail.com> > >> > >> > > > > > > wrote: > >> > >> > > > > > > >> > selectively reading from sockets achieves memory > >> > control > >> > >> (up > >> > >> > > to > >> > >> > > > > and > >> > >> > > > > > > not > >> > >> > > > > > > >> > including talk of (de)compression) > >> > >> > > > > > > >> > > >> > >> > > > > > > >> > this is exactly what i (also, even mostly) did for > >> > kip-72 > >> > >> - > >> > >> > > > which > >> > >> > > > > i > >> > >> > > > > > > hope > >> > >> > > > > > > >> in > >> > >> > > > > > > >> > itself should be a reason to think about both KIPs > >> at > >> > the > >> > >> > same > >> > >> > > > > time > >> > >> > > > > > > >> because > >> > >> > > > > > > >> > the changes will be similar (at least in intent) > and > >> > might > >> > >> > > > result > >> > >> > > > > in > >> > >> > > > > > > >> > duplicated effort. > >> > >> > > > > > > >> > > >> > >> > > > > > > >> > a pool API is a way to "scale" all the way from > just > >> > >> > > > maintaining a > >> > >> > > > > > > >> variable > >> > >> > > > > > > >> > holding amount of available memory (which is what > my > >> > >> current > >> > >> > > > > kip-72 > >> > >> > > > > > > code > >> > >> > > > > > > >> > does and what this kip proposes IIUC) all the way > up > >> to > >> > >> > > actually > >> > >> > > > > > > re-using > >> > >> > > > > > > >> > buffers without any changes to the code using the > >> pool > >> > - > >> > >> > just > >> > >> > > > drop > >> > >> > > > > > in > >> > >> > > > > > > a > >> > >> > > > > > > >> > different pool impl. > >> > >> > > > > > > >> > > >> > >> > > > > > > >> > for "edge nodes" (producer/consumer) the > performance > >> > gain > >> > >> in > >> > >> > > > > > actually > >> > >> > > > > > > >> > pooling large buffers may be arguable, but i > suspect > >> > for > >> > >> > > brokers > >> > >> > > > > > > >> regularly > >> > >> > > > > > > >> > operating on 1MB-sized requests (which is the norm > >> at > >> > >> > > linkedin) > >> > >> > > > > the > >> > >> > > > > > > >> > resulting memory fragmentation is an actual > >> bottleneck > >> > (i > >> > >> > have > >> > >> > > > > > initial > >> > >> > > > > > > >> > micro-benchmark results to back this up but have > not > >> > had > >> > >> the > >> > >> > > > time > >> > >> > > > > to > >> > >> > > > > > > do a > >> > >> > > > > > > >> > full profiling run). > >> > >> > > > > > > >> > > >> > >> > > > > > > >> > so basically I'm saying we may be doing (very) > >> similar > >> > >> > things > >> > >> > > in > >> > >> > > > > > > mostly > >> > >> > > > > > > >> the > >> > >> > > > > > > >> > same areas of code. > >> > >> > > > > > > >> > > >> > >> > > > > > > >> > On Wed, Nov 2, 2016 at 11:35 AM, Mickael Maison < > >> > >> > > > > > > >> mickael.mai...@gmail.com> > >> > >> > > > > > > >> > wrote: > >> > >> > > > > > > >> > > >> > >> > > > > > > >> >> electively reading from the socket should enable > to > >> > >> > > > > > > >> >> control the memory usage without impacting > >> > performance. > >> > >> > I've > >> > >> > > > had > >> > >> > > > > > look > >> > >> > > > > > > >> >> at that today and I can see how that would work. > >> > >> > > > > > > >> >> I'll update the KIP accordingly tomorrow. > >> > >> > > > > > > >> >> > >> > >> > > > > > > >> > >> > >> > > > > > > > >> > >> > > > > > > >> > >> > > > > > >> > >> > > > > >> > >> > > > >> > >> > > >> > >> > >> > > >> > >> > >> > >> -- > >> Regards, > >> > >> Rajini > >> > >> > >> > >> Unless stated otherwise above: > >> IBM United Kingdom Limited - Registered in England and Wales with number > >> 741598. > >> Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 > 3AU > >> >
