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 >>
