I think taking bigger one of the fetch size and message size limit is probably good enough. If we have a separate "offset.replica.fetch.max.bytes", I guess the value will always be set to max message size of the __consumer_offsets topic, which does not seem to have much value.
On Thu, Jun 9, 2016 at 3:15 AM, Onur Karaman <okara...@linkedin.com.invalid> wrote: > Maybe another approach can be to add a new > "offsets.replica.fetch.max.bytes" config on the brokers. > > On Thu, Jun 9, 2016 at 3:03 AM, Onur Karaman <okara...@linkedin.com> > wrote: > > > I made a PR with a tweak to Jun's/Becket's proposal: > > https://github.com/apache/kafka/pull/1484 > > > > It just tweaks the fetch behavior specifically for replicas fetching from > > the __consumer_offsets topic when the fetcher's "replica.fetch.max.bytes" > > is less than the __consumer_offset leader's "message.max.bytes" to take > the > > max of the two. > > > > I'm honestly not that happy with this solution, as I'd rather not change > > the "replica.fetch.max.bytes" config from being a limit to a > > recommendation. I'd definitely be happy to hear other alternatives! > > > > On Sun, May 29, 2016 at 1:57 PM, Onur Karaman < > > onurkaraman.apa...@gmail.com> wrote: > > > >> Sorry I know next to nothing about Kafka Connect. I didn't understand > the > >> Kafka Connect / MM idea you brought up. Can you go into more detail? > >> > >> Otherwise I think our remaining options are: > >> - Jun's suggestion to bump up the KafkaConfig.messageMaxBytes for > >> __consumer_offsets topic and change the fetch behavior when message size > >> is > >> larger than fetch size > >> - option 6: support sending the regex over the wire instead of the fully > >> expanded topic subscriptions. This should cut down the message size from > >> the subscription side. Again this only helps when pattern-based > >> subscriptions are done. > >> > >> minor correction to an earlier comment I made regarding the message > size: > >> message size ~ sum(s_i + a_i for i in range [1, |C|]) > >> > >> On Thu, May 26, 2016 at 3:35 PM, Jason Gustafson <ja...@confluent.io> > >> wrote: > >> > >> > Hey Onur, > >> > > >> > Thanks for the investigation. It seems the conclusion is that the > >> compact > >> > format helps, but perhaps not enough to justify adding a new > assignment > >> > schema? I'm not sure there's much more room for savings unless we > change > >> > something more fundamental in the assignment approach. We spent some > >> time > >> > thinking before about whether we could let the consumers compute their > >> > assignment locally from a smaller set of information, but the > difficulty > >> > (I'm sure you remember) is reaching consensus on topic metadata. Kafka > >> > Connect has a similar problem where all the workers need to agree on > >> > connector configurations. Since all configs are stored in a single > topic > >> > partition, the approach we take there is to propagate the offset in > the > >> > assignment protocol. Not sure if we could do something similar for > MM... > >> > Anyway, it seems like the best workaround at the moment is Jun's > initial > >> > suggestion. What do you think? > >> > > >> > -Jason > >> > > >> > On Wed, May 25, 2016 at 10:47 PM, Onur Karaman < > >> > onurkaraman.apa...@gmail.com > >> > > wrote: > >> > > >> > > I gave the topic index assignment trick a try against the same > >> > environment. > >> > > The implementation just changed the assignment serialization and > >> > > deserialization logic. It didn't change SyncGroupResponse, meaning > it > >> > > continues to exclude the subscription from the SyncGroupResponse and > >> > > assumes the member has kept track of its last subscription. > >> > > > >> > > Assignment topic indexing with compression: > >> > > 1 consumer 34346 bytes > >> > > 5 consumers 177687 bytes > >> > > 10 consumers 331897 bytes > >> > > 20 consumers 572467 bytes > >> > > 30 consumers 811269 bytes > >> > > 40 consumers 1047188 bytes * the tipping point > >> > > 50 consumers 1290092 bytes > >> > > 60 consumers 1527806 bytes > >> > > 70 consumers 1769259 bytes > >> > > 80 consumers 2000118 bytes > >> > > 90 consumers 2244392 bytes > >> > > 100 consumers 2482415 bytes > >> > > > >> > > Assignment topic indexing without compression: > >> > > 1 consumer 211904 bytes > >> > > 5 consumers 677184 bytes > >> > > 10 consumers 1211154 bytes * the tipping point > >> > > 20 consumers 2136196 bytes > >> > > 30 consumers 3061238 bytes > >> > > 40 consumers 3986280 bytes > >> > > 50 consumers 4911322 bytes > >> > > 60 consumers 5836284 bytes > >> > > 70 consumers 6761246 bytes > >> > > 80 consumers 7686208 bytes > >> > > 90 consumers 8611170 bytes > >> > > 100 consumers 9536132 bytes > >> > > > >> > > Assignment topic indexing seems to reduce the size by 500KB without > >> > > compression and 80KB with compression. So assignment topic indexing > >> makes > >> > > some difference in both with and without compression but in our case > >> was > >> > > not nearly enough. > >> > > > >> > > This can be explained by the fact that we aren't actually hitting > the > >> > worst > >> > > case scenario of each consumer being assigned a partition from every > >> > topic. > >> > > The reason is simple: a topic can only fully span all the consumers > >> if it > >> > > has at least as many partitions as there are consumers. Given that > >> there > >> > > are 8 partitions per topic and we have 100 consumers, it makes sense > >> that > >> > > we aren't close to this worse case scenario where topic indexing > would > >> > make > >> > > a bigger difference. > >> > > > >> > > I tweaked the group leader's assignment code to print out the > >> assignments > >> > > and found that each consumer was getting either 238 or 239 > partitions. > >> > Each > >> > > of these partitions were from unique topics. So the consumers were > >> really > >> > > getting partitions from 239 topics instead of the full worst case > >> > scenario > >> > > of 3000 topics. > >> > > > >> > > On Wed, May 25, 2016 at 1:42 PM, Jason Gustafson < > ja...@confluent.io> > >> > > wrote: > >> > > > >> > > > Gwen, Joel: > >> > > > > >> > > > That's correct. The protocol does allow us to give an assignor its > >> own > >> > > > assignment schema, but I think this will require a couple internal > >> > > changes > >> > > > to the consumer to make use of the full generality. > >> > > > > >> > > > One thing I'm a little uncertain about is whether we should use a > >> > > different > >> > > > protocol type. For a little context, the group membership protocol > >> > allows > >> > > > the client to provide a "protocol type" when joining the group to > >> > ensure > >> > > > that all members have some basic semantic compatibility. For > >> example, > >> > the > >> > > > consumer uses "consumer" and Kafka Connect uses "connect." > Currently > >> > all > >> > > > assignors using the "consumer" protocol share a common schema for > >> > > > representing subscriptions and assignment. This is convenient for > >> tools > >> > > > (like consumer-groups.sh) since they just need to know how to > parse > >> the > >> > > > "consumer" protocol type without knowing anything about the > >> assignors. > >> > So > >> > > > introducing another schema would break that assumption and we'd > need > >> > > those > >> > > > tools to do assignor-specific parsing. Maybe this is OK? > >> Alternatively, > >> > > we > >> > > > could use a separate protocol type (e.g. "compact-consumer"), but > >> that > >> > > > seems less than desirable. > >> > > > > >> > > > Thanks, > >> > > > Jason > >> > > > > >> > > > On Wed, May 25, 2016 at 11:00 AM, Gwen Shapira <g...@confluent.io > > > >> > > wrote: > >> > > > > >> > > > > ah, right - we can add as many strategies as we want. > >> > > > > > >> > > > > On Wed, May 25, 2016 at 10:54 AM, Joel Koshy < > jjkosh...@gmail.com > >> > > >> > > > wrote: > >> > > > > > >> > > > > > > Yes it would be a protocol bump. > >> > > > > > > > >> > > > > > > >> > > > > > Sorry - I'm officially confused. I think it may not be > required > >> - > >> > > since > >> > > > > the > >> > > > > > more compact format would be associated with a new assignment > >> > > strategy > >> > > > - > >> > > > > > right? > >> > > > > > > >> > > > > > > >> > > > > > > smaller than the plaintext PAL, but the post-compressed > binary > >> > PAL > >> > > is > >> > > > > > just > >> > > > > > > 25% smaller than the post-compressed plaintext PAL. IOW > using > >> a > >> > > > symbol > >> > > > > > > table helps a lot but further compression on that already > >> compact > >> > > > > format > >> > > > > > > would yield only marginal return. > >> > > > > > > > >> > > > > > > >> > > > > > > So basically I feel we could get pretty far with a more > >> compact > >> > > field > >> > > > > > > format for assignment and if we do that then we would > >> potentially > >> > > not > >> > > > > > even > >> > > > > > > want to do any compression. > >> > > > > > > > >> > > > > > > >> > > > > > Also just wanted to add that this compression on the binary > PAL > >> did > >> > > > help > >> > > > > > but the compression ratio was obviously not as high as > plaintext > >> > > > > > compression. > >> > > > > > > >> > > > > > > >> > > > > > > > >> > > > > > > On Tue, May 24, 2016 at 4:19 PM, Gwen Shapira < > >> g...@confluent.io > >> > > > >> > > > > wrote: > >> > > > > > > > >> > > > > > >> Regarding the change to the assignment field. It would be a > >> > > protocol > >> > > > > > bump, > >> > > > > > >> otherwise consumers will not know how to parse the bytes > the > >> > > broker > >> > > > is > >> > > > > > >> returning, right? > >> > > > > > >> Or did I misunderstand the suggestion? > >> > > > > > >> > >> > > > > > >> On Tue, May 24, 2016 at 2:52 PM, Guozhang Wang < > >> > > wangg...@gmail.com> > >> > > > > > >> wrote: > >> > > > > > >> > >> > > > > > >> > I think for just solving issue 1), Jun's suggestion is > >> > > sufficient > >> > > > > and > >> > > > > > >> > simple. So I'd prefer that approach. > >> > > > > > >> > > >> > > > > > >> > In addition, Jason's optimization on the assignment field > >> > would > >> > > be > >> > > > > > good > >> > > > > > >> for > >> > > > > > >> > 2) and 3) as well, and I like that optimization for its > >> > > simplicity > >> > > > > and > >> > > > > > >> no > >> > > > > > >> > format change as well. And in the future I'm in favor of > >> > > > considering > >> > > > > > to > >> > > > > > >> > change the in-memory cache format as Jiangjie suggested. > >> > > > > > >> > > >> > > > > > >> > Guozhang > >> > > > > > >> > > >> > > > > > >> > > >> > > > > > >> > On Tue, May 24, 2016 at 12:42 PM, Becket Qin < > >> > > > becket....@gmail.com> > >> > > > > > >> wrote: > >> > > > > > >> > > >> > > > > > >> > > Hi Jason, > >> > > > > > >> > > > >> > > > > > >> > > There are a few problems we want to solve here: > >> > > > > > >> > > 1. The group metadata is too big to be appended to the > >> log. > >> > > > > > >> > > 2. Reduce the memory footprint on the broker > >> > > > > > >> > > 3. Reduce the bytes transferred over the wire. > >> > > > > > >> > > > >> > > > > > >> > > To solve (1), I like your idea of having separate > >> messages > >> > per > >> > > > > > member. > >> > > > > > >> > The > >> > > > > > >> > > proposal (Onur's option 8) is to break metadata into > >> small > >> > > > records > >> > > > > > in > >> > > > > > >> the > >> > > > > > >> > > same uncompressed message set so each record is small. > I > >> > agree > >> > > > it > >> > > > > > >> would > >> > > > > > >> > be > >> > > > > > >> > > ideal if we are able to store the metadata separately > for > >> > each > >> > > > > > >> member. I > >> > > > > > >> > > was also thinking about storing the metadata into > >> multiple > >> > > > > messages, > >> > > > > > >> too. > >> > > > > > >> > > What concerns me was that having multiple messages > seems > >> > > > breaking > >> > > > > > the > >> > > > > > >> > > atomicity. I am not sure how we are going to deal with > >> the > >> > > > > potential > >> > > > > > >> > > issues. For example, What if group metadata is > replicated > >> > but > >> > > > the > >> > > > > > >> member > >> > > > > > >> > > metadata is not? It might be fine depending on the > >> > > > implementation > >> > > > > > >> though, > >> > > > > > >> > > but I am not sure. > >> > > > > > >> > > > >> > > > > > >> > > For (2) we want to store the metadata onto the disk, > >> which > >> > is > >> > > > what > >> > > > > > we > >> > > > > > >> > have > >> > > > > > >> > > to do anyway. The only question is in what format > should > >> we > >> > > > store > >> > > > > > >> them. > >> > > > > > >> > > > >> > > > > > >> > > To address (3) we want to have the metadata to be > >> > compressed, > >> > > > > which > >> > > > > > is > >> > > > > > >> > > contradict to the the above solution of (1). > >> > > > > > >> > > > >> > > > > > >> > > I think Jun's suggestion is probably still the > simplest. > >> To > >> > > > avoid > >> > > > > > >> > changing > >> > > > > > >> > > the behavior for consumers, maybe we can do that only > for > >> > > > > > >> offset_topic, > >> > > > > > >> > > i.e, if the max fetch bytes of the fetch request is > >> smaller > >> > > than > >> > > > > the > >> > > > > > >> > > message size on the offset topic, we always return at > >> least > >> > > one > >> > > > > full > >> > > > > > >> > > message. This should avoid the unexpected problem on > the > >> > > client > >> > > > > side > >> > > > > > >> > > because supposedly only tools and brokers will fetch > from > >> > the > >> > > > the > >> > > > > > >> > internal > >> > > > > > >> > > topics, > >> > > > > > >> > > > >> > > > > > >> > > As a modification to what you suggested, one solution I > >> was > >> > > > > thinking > >> > > > > > >> was > >> > > > > > >> > to > >> > > > > > >> > > have multiple messages in a single compressed message. > >> That > >> > > > means > >> > > > > > for > >> > > > > > >> > > SyncGroupResponse we still need to read the entire > >> > compressed > >> > > > > > messages > >> > > > > > >> > and > >> > > > > > >> > > extract the inner messages, which seems not quite > >> different > >> > > from > >> > > > > > >> having a > >> > > > > > >> > > single message containing everything. But let me just > >> put it > >> > > > here > >> > > > > > and > >> > > > > > >> see > >> > > > > > >> > > if that makes sense. > >> > > > > > >> > > > >> > > > > > >> > > We can have a map of GroupMetadataKey -> > >> > > > GroupMetadataValueOffset. > >> > > > > > >> > > > >> > > > > > >> > > The GroupMetadataValue is stored in a compressed > message. > >> > The > >> > > > > inner > >> > > > > > >> > > messages are the following: > >> > > > > > >> > > > >> > > > > > >> > > Inner Message 0: Version GroupId Generation > >> > > > > > >> > > > >> > > > > > >> > > Inner Message 1: MemberId MemberMetadata_1 (we can > >> compress > >> > > the > >> > > > > > bytes > >> > > > > > >> > here) > >> > > > > > >> > > > >> > > > > > >> > > Inner Message 2: MemberId MemberMetadata_2 > >> > > > > > >> > > .... > >> > > > > > >> > > Inner Message N: MemberId MemberMetadata_N > >> > > > > > >> > > > >> > > > > > >> > > The MemberMetadata format is the following: > >> > > > > > >> > > MemberMetadata => Version Generation ClientId Host > >> > > > Subscription > >> > > > > > >> > > Assignment > >> > > > > > >> > > > >> > > > > > >> > > So DescribeGroupResponse will just return the entire > >> > > compressed > >> > > > > > >> > > GroupMetadataMessage. SyncGroupResponse will return the > >> > > > > > corresponding > >> > > > > > >> > inner > >> > > > > > >> > > message. > >> > > > > > >> > > > >> > > > > > >> > > Thanks, > >> > > > > > >> > > > >> > > > > > >> > > Jiangjie (Becket) Qin > >> > > > > > >> > > > >> > > > > > >> > > > >> > > > > > >> > > > >> > > > > > >> > > On Tue, May 24, 2016 at 9:14 AM, Jason Gustafson < > >> > > > > > ja...@confluent.io> > >> > > > > > >> > > wrote: > >> > > > > > >> > > > >> > > > > > >> > > > Hey Becket, > >> > > > > > >> > > > > >> > > > > > >> > > > I like your idea to store only the offset for the > group > >> > > > metadata > >> > > > > > in > >> > > > > > >> > > memory. > >> > > > > > >> > > > I think it would be safe to keep it in memory for a > >> short > >> > > time > >> > > > > > after > >> > > > > > >> > the > >> > > > > > >> > > > rebalance completes, but after that, it's only real > >> > purpose > >> > > is > >> > > > > to > >> > > > > > >> > answer > >> > > > > > >> > > > DescribeGroup requests, so your proposal makes a lot > of > >> > > sense > >> > > > to > >> > > > > > me. > >> > > > > > >> > > > > >> > > > > > >> > > > As for the specific problem with the size of the > group > >> > > > metadata > >> > > > > > >> message > >> > > > > > >> > > for > >> > > > > > >> > > > the MM case, if we cannot succeed in reducing the > size > >> of > >> > > the > >> > > > > > >> > > > subscription/assignment (which I think is still > >> probably > >> > the > >> > > > > best > >> > > > > > >> > > > alternative if it can work), then I think there are > >> some > >> > > > options > >> > > > > > for > >> > > > > > >> > > > changing the message format (option #8 in Onur's > >> initial > >> > > > > e-mail). > >> > > > > > >> > > > Currently, the key used for storing the group > metadata > >> is > >> > > > this: > >> > > > > > >> > > > > >> > > > > > >> > > > GroupMetadataKey => Version GroupId > >> > > > > > >> > > > > >> > > > > > >> > > > And the value is something like this (some details > >> > elided): > >> > > > > > >> > > > > >> > > > > > >> > > > GroupMetadataValue => Version GroupId Generation > >> > > > > [MemberMetadata] > >> > > > > > >> > > > MemberMetadata => ClientId Host Subscription > >> Assignment > >> > > > > > >> > > > > >> > > > > > >> > > > I don't think we can change the key without a lot of > >> pain, > >> > > but > >> > > > > it > >> > > > > > >> seems > >> > > > > > >> > > > like we can change the value format. Maybe we can > take > >> the > >> > > > > > >> > > > subscription/assignment payloads out of the value and > >> > > > introduce > >> > > > > a > >> > > > > > >> new > >> > > > > > >> > > > "MemberMetadata" message for each member in the > group. > >> For > >> > > > > > example: > >> > > > > > >> > > > > >> > > > > > >> > > > MemberMetadataKey => Version GroupId MemberId > >> > > > > > >> > > > > >> > > > > > >> > > > MemberMetadataValue => Version Generation ClientId > Host > >> > > > > > Subscription > >> > > > > > >> > > > Assignment > >> > > > > > >> > > > > >> > > > > > >> > > > When a new generation is created, we would first > write > >> the > >> > > > group > >> > > > > > >> > metadata > >> > > > > > >> > > > message which includes the generation and all of the > >> > > > memberIds, > >> > > > > > and > >> > > > > > >> > then > >> > > > > > >> > > > we'd write the member metadata messages. To answer > the > >> > > > > > DescribeGroup > >> > > > > > >> > > > request, we'd read the group metadata at the cached > >> offset > >> > > > and, > >> > > > > > >> > depending > >> > > > > > >> > > > on the version, all of the following member metadata. > >> This > >> > > > would > >> > > > > > be > >> > > > > > >> > more > >> > > > > > >> > > > complex to maintain, but it seems doable if it comes > to > >> > it. > >> > > > > > >> > > > > >> > > > > > >> > > > Thanks, > >> > > > > > >> > > > Jason > >> > > > > > >> > > > > >> > > > > > >> > > > On Mon, May 23, 2016 at 6:15 PM, Becket Qin < > >> > > > > becket....@gmail.com > >> > > > > > > > >> > > > > > >> > > wrote: > >> > > > > > >> > > > > >> > > > > > >> > > > > It might worth thinking a little further. We have > >> > > discussed > >> > > > > this > >> > > > > > >> > before > >> > > > > > >> > > > > that we want to avoid holding all the group > metadata > >> in > >> > > > > memory. > >> > > > > > >> > > > > > >> > > > > > >> > > > > I am thinking about the following end state: > >> > > > > > >> > > > > > >> > > > > > >> > > > > 1. Enable compression on the offset topic. > >> > > > > > >> > > > > 2. Instead of holding the entire group metadata in > >> > memory > >> > > on > >> > > > > the > >> > > > > > >> > > brokers, > >> > > > > > >> > > > > each broker only keeps a [group -> Offset] map, the > >> > offset > >> > > > > > points > >> > > > > > >> to > >> > > > > > >> > > the > >> > > > > > >> > > > > message in the offset topic which holds the latest > >> > > metadata > >> > > > of > >> > > > > > the > >> > > > > > >> > > group. > >> > > > > > >> > > > > 3. DescribeGroupResponse will read from the offset > >> topic > >> > > > > > directly > >> > > > > > >> > like > >> > > > > > >> > > a > >> > > > > > >> > > > > normal consumption, except that only exactly one > >> message > >> > > > will > >> > > > > be > >> > > > > > >> > > > returned. > >> > > > > > >> > > > > 4. SyncGroupResponse will read the message, extract > >> the > >> > > > > > assignment > >> > > > > > >> > part > >> > > > > > >> > > > and > >> > > > > > >> > > > > send back the partition assignment. We can compress > >> the > >> > > > > > partition > >> > > > > > >> > > > > assignment before sends it out if we want. > >> > > > > > >> > > > > > >> > > > > > >> > > > > Jiangjie (Becket) Qin > >> > > > > > >> > > > > > >> > > > > > >> > > > > On Mon, May 23, 2016 at 5:08 PM, Jason Gustafson < > >> > > > > > >> ja...@confluent.io > >> > > > > > >> > > > >> > > > > > >> > > > > wrote: > >> > > > > > >> > > > > > >> > > > > > >> > > > > > > > >> > > > > > >> > > > > > > Jason, doesn't gzip (or other compression) > >> basically > >> > > do > >> > > > > > this? > >> > > > > > >> If > >> > > > > > >> > > the > >> > > > > > >> > > > > > topic > >> > > > > > >> > > > > > > is a string and the topic is repeated > throughout, > >> > > won't > >> > > > > > >> > compression > >> > > > > > >> > > > > > > basically replace all repeated instances of it > >> with > >> > an > >> > > > > index > >> > > > > > >> > > > reference > >> > > > > > >> > > > > to > >> > > > > > >> > > > > > > the full string? > >> > > > > > >> > > > > > > >> > > > > > >> > > > > > > >> > > > > > >> > > > > > Hey James, yeah, that's probably true, but keep > in > >> > mind > >> > > > that > >> > > > > > the > >> > > > > > >> > > > > > compression happens on the broker side. It would > be > >> > nice > >> > > > to > >> > > > > > >> have a > >> > > > > > >> > > more > >> > > > > > >> > > > > > compact representation so that get some benefit > >> over > >> > the > >> > > > > wire > >> > > > > > as > >> > > > > > >> > > well. > >> > > > > > >> > > > > This > >> > > > > > >> > > > > > seems to be less of a concern here, so the bigger > >> > gains > >> > > > are > >> > > > > > >> > probably > >> > > > > > >> > > > from > >> > > > > > >> > > > > > reducing the number of partitions that need to be > >> > listed > >> > > > > > >> > > individually. > >> > > > > > >> > > > > > > >> > > > > > >> > > > > > -Jason > >> > > > > > >> > > > > > > >> > > > > > >> > > > > > On Mon, May 23, 2016 at 4:23 PM, Onur Karaman < > >> > > > > > >> > > > > > onurkaraman.apa...@gmail.com> > >> > > > > > >> > > > > > wrote: > >> > > > > > >> > > > > > > >> > > > > > >> > > > > > > When figuring out these optimizations, it's > worth > >> > > > keeping > >> > > > > in > >> > > > > > >> mind > >> > > > > > >> > > the > >> > > > > > >> > > > > > > improvements when the message is uncompressed > vs > >> > when > >> > > > it's > >> > > > > > >> > > > compressed. > >> > > > > > >> > > > > > > > >> > > > > > >> > > > > > > When uncompressed: > >> > > > > > >> > > > > > > Fixing the Assignment serialization to instead > >> be a > >> > > > topic > >> > > > > > >> index > >> > > > > > >> > > into > >> > > > > > >> > > > > the > >> > > > > > >> > > > > > > corresponding member's subscription list would > >> > usually > >> > > > be > >> > > > > a > >> > > > > > >> good > >> > > > > > >> > > > thing. > >> > > > > > >> > > > > > > > >> > > > > > >> > > > > > > I think the proposal is only worse when the > topic > >> > > names > >> > > > > are > >> > > > > > >> > small. > >> > > > > > >> > > > The > >> > > > > > >> > > > > > > Type.STRING we use in our protocol for the > >> > > assignment's > >> > > > > > >> > > > TOPIC_KEY_NAME > >> > > > > > >> > > > > is > >> > > > > > >> > > > > > > limited in length to Short.MAX_VALUE, so our > >> strings > >> > > are > >> > > > > > first > >> > > > > > >> > > > > prepended > >> > > > > > >> > > > > > > with 2 bytes to indicate the string size. > >> > > > > > >> > > > > > > > >> > > > > > >> > > > > > > The new proposal does worse when: > >> > > > > > >> > > > > > > 2 + utf_encoded_string_payload_size < > >> > index_type_size > >> > > > > > >> > > > > > > in other words when: > >> > > > > > >> > > > > > > utf_encoded_string_payload_size < > >> index_type_size - > >> > 2 > >> > > > > > >> > > > > > > > >> > > > > > >> > > > > > > If the index type ends up being Type.INT32, > then > >> the > >> > > > > > proposal > >> > > > > > >> is > >> > > > > > >> > > > worse > >> > > > > > >> > > > > > when > >> > > > > > >> > > > > > > the topic is length 1. > >> > > > > > >> > > > > > > If the index type ends up being Type.INT64, > then > >> the > >> > > > > > proposal > >> > > > > > >> is > >> > > > > > >> > > > worse > >> > > > > > >> > > > > > when > >> > > > > > >> > > > > > > the topic is less than length 6. > >> > > > > > >> > > > > > > > >> > > > > > >> > > > > > > When compressed: > >> > > > > > >> > > > > > > As James Cheng brought up, I'm not sure how > >> things > >> > > > change > >> > > > > > when > >> > > > > > >> > > > > > compression > >> > > > > > >> > > > > > > comes into the picture. This would be worth > >> > > > investigating. > >> > > > > > >> > > > > > > > >> > > > > > >> > > > > > > On Mon, May 23, 2016 at 4:05 PM, James Cheng < > >> > > > > > >> > wushuja...@gmail.com > >> > > > > > >> > > > > >> > > > > > >> > > > > > wrote: > >> > > > > > >> > > > > > > > >> > > > > > >> > > > > > > > > >> > > > > > >> > > > > > > > > On May 23, 2016, at 10:59 AM, Jason > >> Gustafson < > >> > > > > > >> > > > ja...@confluent.io> > >> > > > > > >> > > > > > > > wrote: > >> > > > > > >> > > > > > > > > > >> > > > > > >> > > > > > > > > 2. Maybe there's a better way to lay out > the > >> > > > > assignment > >> > > > > > >> > without > >> > > > > > >> > > > > > needing > >> > > > > > >> > > > > > > > to > >> > > > > > >> > > > > > > > > explicitly repeat the topic? For example, > the > >> > > leader > >> > > > > > could > >> > > > > > >> > sort > >> > > > > > >> > > > the > >> > > > > > >> > > > > > > > topics > >> > > > > > >> > > > > > > > > for each member and just use an integer to > >> > > represent > >> > > > > the > >> > > > > > >> > index > >> > > > > > >> > > of > >> > > > > > >> > > > > > each > >> > > > > > >> > > > > > > > > topic within the sorted list (note this > >> depends > >> > on > >> > > > the > >> > > > > > >> > > > subscription > >> > > > > > >> > > > > > > > > including the full topic list). > >> > > > > > >> > > > > > > > > > >> > > > > > >> > > > > > > > > Assignment -> [TopicIndex [Partition]] > >> > > > > > >> > > > > > > > > > >> > > > > > >> > > > > > > > > >> > > > > > >> > > > > > > > Jason, doesn't gzip (or other compression) > >> > basically > >> > > > do > >> > > > > > >> this? > >> > > > > > >> > If > >> > > > > > >> > > > the > >> > > > > > >> > > > > > > topic > >> > > > > > >> > > > > > > > is a string and the topic is repeated > >> throughout, > >> > > > won't > >> > > > > > >> > > compression > >> > > > > > >> > > > > > > > basically replace all repeated instances of > it > >> > with > >> > > an > >> > > > > > index > >> > > > > > >> > > > > reference > >> > > > > > >> > > > > > to > >> > > > > > >> > > > > > > > the full string? > >> > > > > > >> > > > > > > > > >> > > > > > >> > > > > > > > -James > >> > > > > > >> > > > > > > > > >> > > > > > >> > > > > > > > > You could even combine these two options so > >> that > >> > > you > >> > > > > > have > >> > > > > > >> > only > >> > > > > > >> > > 3 > >> > > > > > >> > > > > > > integers > >> > > > > > >> > > > > > > > > for each topic assignment: > >> > > > > > >> > > > > > > > > > >> > > > > > >> > > > > > > > > Assignment -> [TopicIndex MinPartition > >> > > MaxPartition] > >> > > > > > >> > > > > > > > > > >> > > > > > >> > > > > > > > > There may even be better options with a > >> little > >> > > more > >> > > > > > >> thought. > >> > > > > > >> > > All > >> > > > > > >> > > > of > >> > > > > > >> > > > > > > this > >> > > > > > >> > > > > > > > is > >> > > > > > >> > > > > > > > > just part of the client-side protocol, so > it > >> > > > wouldn't > >> > > > > > >> require > >> > > > > > >> > > any > >> > > > > > >> > > > > > > version > >> > > > > > >> > > > > > > > > bumps on the broker. What do you think? > >> > > > > > >> > > > > > > > > > >> > > > > > >> > > > > > > > > Thanks, > >> > > > > > >> > > > > > > > > Jason > >> > > > > > >> > > > > > > > > > >> > > > > > >> > > > > > > > > > >> > > > > > >> > > > > > > > > > >> > > > > > >> > > > > > > > > > >> > > > > > >> > > > > > > > > On Mon, May 23, 2016 at 9:17 AM, Guozhang > >> Wang < > >> > > > > > >> > > > wangg...@gmail.com > >> > > > > > >> > > > > > > >> > > > > > >> > > > > > > > wrote: > >> > > > > > >> > > > > > > > > > >> > > > > > >> > > > > > > > >> The original concern is that regex may not > >> be > >> > > > > > efficiently > >> > > > > > >> > > > > supported > >> > > > > > >> > > > > > > > >> across-languages, but if there is a neat > >> > > > workaround I > >> > > > > > >> would > >> > > > > > >> > > love > >> > > > > > >> > > > > to > >> > > > > > >> > > > > > > > learn. > >> > > > > > >> > > > > > > > >> > >> > > > > > >> > > > > > > > >> Guozhang > >> > > > > > >> > > > > > > > >> > >> > > > > > >> > > > > > > > >> On Mon, May 23, 2016 at 5:31 AM, Ismael > >> Juma < > >> > > > > > >> > > ism...@juma.me.uk > >> > > > > > >> > > > > > >> > > > > > >> > > > > > > wrote: > >> > > > > > >> > > > > > > > >> > >> > > > > > >> > > > > > > > >>> +1 to Jun's suggestion. > >> > > > > > >> > > > > > > > >>> > >> > > > > > >> > > > > > > > >>> Having said that, as a general point, I > >> think > >> > we > >> > > > > > should > >> > > > > > >> > > > consider > >> > > > > > >> > > > > > > > >> supporting > >> > > > > > >> > > > > > > > >>> topic patterns in the wire protocol. It > >> > requires > >> > > > > some > >> > > > > > >> > > thinking > >> > > > > > >> > > > > for > >> > > > > > >> > > > > > > > >>> cross-language support, but it seems > >> > > surmountable > >> > > > > and > >> > > > > > it > >> > > > > > >> > > could > >> > > > > > >> > > > > make > >> > > > > > >> > > > > > > > >> certain > >> > > > > > >> > > > > > > > >>> operations a lot more efficient (the fact > >> > that a > >> > > > > basic > >> > > > > > >> > regex > >> > > > > > >> > > > > > > > subscription > >> > > > > > >> > > > > > > > >>> causes the consumer to request metadata > for > >> > all > >> > > > > topics > >> > > > > > >> is > >> > > > > > >> > not > >> > > > > > >> > > > > > great). > >> > > > > > >> > > > > > > > >>> > >> > > > > > >> > > > > > > > >>> Ismael > >> > > > > > >> > > > > > > > >>> > >> > > > > > >> > > > > > > > >>> On Sun, May 22, 2016 at 11:49 PM, > Guozhang > >> > Wang > >> > > < > >> > > > > > >> > > > > > wangg...@gmail.com> > >> > > > > > >> > > > > > > > >>> wrote: > >> > > > > > >> > > > > > > > >>> > >> > > > > > >> > > > > > > > >>>> I like Jun's suggestion in changing the > >> > > handling > >> > > > > > >> logics of > >> > > > > > >> > > > > single > >> > > > > > >> > > > > > > > large > >> > > > > > >> > > > > > > > >>>> message on the consumer side. > >> > > > > > >> > > > > > > > >>>> > >> > > > > > >> > > > > > > > >>>> As for the case of "a single group > >> > subscribing > >> > > to > >> > > > > > 3000 > >> > > > > > >> > > > topics", > >> > > > > > >> > > > > > with > >> > > > > > >> > > > > > > > >> 100 > >> > > > > > >> > > > > > > > >>>> consumers the 2.5Mb Gzip size is > >> reasonable > >> > to > >> > > me > >> > > > > > (when > >> > > > > > >> > > > storing > >> > > > > > >> > > > > in > >> > > > > > >> > > > > > > ZK, > >> > > > > > >> > > > > > > > >> we > >> > > > > > >> > > > > > > > >>>> also have the znode limit which is set > to > >> 1Mb > >> > > by > >> > > > > > >> default, > >> > > > > > >> > > > though > >> > > > > > >> > > > > > > > >>> admittedly > >> > > > > > >> > > > > > > > >>>> it is only for one consumer). And if we > do > >> > the > >> > > > > change > >> > > > > > >> as > >> > > > > > >> > Jun > >> > > > > > >> > > > > > > > suggested, > >> > > > > > >> > > > > > > > >>>> 2.5Mb on follower's memory pressure is > OK > >> I > >> > > > think. > >> > > > > > >> > > > > > > > >>>> > >> > > > > > >> > > > > > > > >>>> > >> > > > > > >> > > > > > > > >>>> Guozhang > >> > > > > > >> > > > > > > > >>>> > >> > > > > > >> > > > > > > > >>>> > >> > > > > > >> > > > > > > > >>>> On Sat, May 21, 2016 at 12:51 PM, Onur > >> > Karaman > >> > > < > >> > > > > > >> > > > > > > > >>>> onurkaraman.apa...@gmail.com > >> > > > > > >> > > > > > > > >>>>> wrote: > >> > > > > > >> > > > > > > > >>>> > >> > > > > > >> > > > > > > > >>>>> Results without compression: > >> > > > > > >> > > > > > > > >>>>> 1 consumer 292383 bytes > >> > > > > > >> > > > > > > > >>>>> 5 consumers 1079579 bytes * the tipping > >> > point > >> > > > > > >> > > > > > > > >>>>> 10 consumers 1855018 bytes > >> > > > > > >> > > > > > > > >>>>> 20 consumers 2780220 bytes > >> > > > > > >> > > > > > > > >>>>> 30 consumers 3705422 bytes > >> > > > > > >> > > > > > > > >>>>> 40 consumers 4630624 bytes > >> > > > > > >> > > > > > > > >>>>> 50 consumers 5555826 bytes > >> > > > > > >> > > > > > > > >>>>> 60 consumers 6480788 bytes > >> > > > > > >> > > > > > > > >>>>> 70 consumers 7405750 bytes > >> > > > > > >> > > > > > > > >>>>> 80 consumers 8330712 bytes > >> > > > > > >> > > > > > > > >>>>> 90 consumers 9255674 bytes > >> > > > > > >> > > > > > > > >>>>> 100 consumers 10180636 bytes > >> > > > > > >> > > > > > > > >>>>> > >> > > > > > >> > > > > > > > >>>>> So it looks like gzip compression > shrinks > >> > the > >> > > > > > message > >> > > > > > >> > size > >> > > > > > >> > > by > >> > > > > > >> > > > > 4x. > >> > > > > > >> > > > > > > > >>>>> > >> > > > > > >> > > > > > > > >>>>> On Sat, May 21, 2016 at 9:47 AM, Jun > Rao > >> < > >> > > > > > >> > j...@confluent.io > >> > > > > > >> > > > > >> > > > > > >> > > > > > wrote: > >> > > > > > >> > > > > > > > >>>>> > >> > > > > > >> > > > > > > > >>>>>> Onur, > >> > > > > > >> > > > > > > > >>>>>> > >> > > > > > >> > > > > > > > >>>>>> Thanks for the investigation. > >> > > > > > >> > > > > > > > >>>>>> > >> > > > > > >> > > > > > > > >>>>>> Another option is to just fix how we > >> deal > >> > > with > >> > > > > the > >> > > > > > >> case > >> > > > > > >> > > > when a > >> > > > > > >> > > > > > > > >>> message > >> > > > > > >> > > > > > > > >>>> is > >> > > > > > >> > > > > > > > >>>>>> larger than the fetch size. Today, if > >> the > >> > > fetch > >> > > > > > size > >> > > > > > >> is > >> > > > > > >> > > > > smaller > >> > > > > > >> > > > > > > > >> than > >> > > > > > >> > > > > > > > >>>> the > >> > > > > > >> > > > > > > > >>>>>> fetch size, the consumer will get > stuck. > >> > > > Instead, > >> > > > > > we > >> > > > > > >> can > >> > > > > > >> > > > > simply > >> > > > > > >> > > > > > > > >>> return > >> > > > > > >> > > > > > > > >>>>> the > >> > > > > > >> > > > > > > > >>>>>> full message if it's larger than the > >> fetch > >> > > size > >> > > > > w/o > >> > > > > > >> > > > requiring > >> > > > > > >> > > > > > the > >> > > > > > >> > > > > > > > >>>>> consumer > >> > > > > > >> > > > > > > > >>>>>> to manually adjust the fetch size. On > >> the > >> > > > broker > >> > > > > > >> side, > >> > > > > > >> > to > >> > > > > > >> > > > > serve > >> > > > > > >> > > > > > a > >> > > > > > >> > > > > > > > >>> fetch > >> > > > > > >> > > > > > > > >>>>>> request, we already do an index lookup > >> and > >> > > then > >> > > > > > scan > >> > > > > > >> the > >> > > > > > >> > > > log a > >> > > > > > >> > > > > > bit > >> > > > > > >> > > > > > > > >> to > >> > > > > > >> > > > > > > > >>>>> find > >> > > > > > >> > > > > > > > >>>>>> the message with the requested offset. > >> We > >> > can > >> > > > > just > >> > > > > > >> check > >> > > > > > >> > > the > >> > > > > > >> > > > > > size > >> > > > > > >> > > > > > > > >> of > >> > > > > > >> > > > > > > > >>>> that > >> > > > > > >> > > > > > > > >>>>>> message and return the full message if > >> its > >> > > size > >> > > > > is > >> > > > > > >> > larger > >> > > > > > >> > > > than > >> > > > > > >> > > > > > the > >> > > > > > >> > > > > > > > >>>> fetch > >> > > > > > >> > > > > > > > >>>>>> size. This way, fetch size is really > for > >> > > > > > performance > >> > > > > > >> > > > > > optimization, > >> > > > > > >> > > > > > > > >>> i.e. > >> > > > > > >> > > > > > > > >>>>> in > >> > > > > > >> > > > > > > > >>>>>> the common case, we will not return > more > >> > > bytes > >> > > > > than > >> > > > > > >> > fetch > >> > > > > > >> > > > > size, > >> > > > > > >> > > > > > > but > >> > > > > > >> > > > > > > > >>> if > >> > > > > > >> > > > > > > > >>>>>> there is a large message, we will > return > >> > more > >> > > > > bytes > >> > > > > > >> than > >> > > > > > >> > > the > >> > > > > > >> > > > > > > > >>> specified > >> > > > > > >> > > > > > > > >>>>>> fetch size. In practice, large > messages > >> are > >> > > > rare. > >> > > > > > >> So, it > >> > > > > > >> > > > > > shouldn't > >> > > > > > >> > > > > > > > >>>>> increase > >> > > > > > >> > > > > > > > >>>>>> the memory consumption on the client > too > >> > > much. > >> > > > > > >> > > > > > > > >>>>>> > >> > > > > > >> > > > > > > > >>>>>> Jun > >> > > > > > >> > > > > > > > >>>>>> > >> > > > > > >> > > > > > > > >>>>>> On Sat, May 21, 2016 at 3:34 AM, Onur > >> > > Karaman < > >> > > > > > >> > > > > > > > >>>>>> onurkaraman.apa...@gmail.com> > >> > > > > > >> > > > > > > > >>>>>> wrote: > >> > > > > > >> > > > > > > > >>>>>> > >> > > > > > >> > > > > > > > >>>>>>> Hey everyone. So I started doing some > >> > tests > >> > > on > >> > > > > the > >> > > > > > >> new > >> > > > > > >> > > > > > > > >>>>>> consumer/coordinator > >> > > > > > >> > > > > > > > >>>>>>> to see if it could handle more > >> strenuous > >> > use > >> > > > > cases > >> > > > > > >> like > >> > > > > > >> > > > > > mirroring > >> > > > > > >> > > > > > > > >>>>>> clusters > >> > > > > > >> > > > > > > > >>>>>>> with thousands of topics and thought > >> I'd > >> > > share > >> > > > > > >> > whatever I > >> > > > > > >> > > > > have > >> > > > > > >> > > > > > so > >> > > > > > >> > > > > > > > >>>> far. > >> > > > > > >> > > > > > > > >>>>>>> > >> > > > > > >> > > > > > > > >>>>>>> The scalability limit: the amount of > >> group > >> > > > > > metadata > >> > > > > > >> we > >> > > > > > >> > > can > >> > > > > > >> > > > > fit > >> > > > > > >> > > > > > > > >> into > >> > > > > > >> > > > > > > > >>>> one > >> > > > > > >> > > > > > > > >>>>>>> message > >> > > > > > >> > > > > > > > >>>>>>> > >> > > > > > >> > > > > > > > >>>>>>> Some background: > >> > > > > > >> > > > > > > > >>>>>>> Client-side assignment is implemented > >> in > >> > two > >> > > > > > phases > >> > > > > > >> > > > > > > > >>>>>>> 1. a PreparingRebalance phase that > >> > > identifies > >> > > > > > >> members > >> > > > > > >> > of > >> > > > > > >> > > > the > >> > > > > > >> > > > > > > > >> group > >> > > > > > >> > > > > > > > >>>> and > >> > > > > > >> > > > > > > > >>>>>>> aggregates member subscriptions. > >> > > > > > >> > > > > > > > >>>>>>> 2. an AwaitingSync phase that waits > for > >> > the > >> > > > > group > >> > > > > > >> > leader > >> > > > > > >> > > to > >> > > > > > >> > > > > > > > >> decide > >> > > > > > >> > > > > > > > >>>>> member > >> > > > > > >> > > > > > > > >>>>>>> assignments based on the member > >> > > subscriptions > >> > > > > > across > >> > > > > > >> > the > >> > > > > > >> > > > > group. > >> > > > > > >> > > > > > > > >>>>>>> - The leader announces this decision > >> > with a > >> > > > > > >> > > > > SyncGroupRequest. > >> > > > > > >> > > > > > > > >> The > >> > > > > > >> > > > > > > > >>>>>>> GroupCoordinator handles > >> SyncGroupRequests > >> > > by > >> > > > > > >> appending > >> > > > > > >> > > all > >> > > > > > >> > > > > > group > >> > > > > > >> > > > > > > > >>>> state > >> > > > > > >> > > > > > > > >>>>>>> into a single message under the > >> > > > > __consumer_offsets > >> > > > > > >> > topic. > >> > > > > > >> > > > > This > >> > > > > > >> > > > > > > > >>>> message > >> > > > > > >> > > > > > > > >>>>> is > >> > > > > > >> > > > > > > > >>>>>>> keyed on the group id and contains > each > >> > > member > >> > > > > > >> > > subscription > >> > > > > > >> > > > > as > >> > > > > > >> > > > > > > > >> well > >> > > > > > >> > > > > > > > >>>> as > >> > > > > > >> > > > > > > > >>>>>> the > >> > > > > > >> > > > > > > > >>>>>>> decided assignment for each member. > >> > > > > > >> > > > > > > > >>>>>>> > >> > > > > > >> > > > > > > > >>>>>>> The environment: > >> > > > > > >> > > > > > > > >>>>>>> - one broker > >> > > > > > >> > > > > > > > >>>>>>> - one __consumer_offsets partition > >> > > > > > >> > > > > > > > >>>>>>> - offsets.topic.compression.codec=1 > // > >> > this > >> > > is > >> > > > > > gzip > >> > > > > > >> > > > > > > > >>>>>>> - broker has my pending KAFKA-3718 > >> patch > >> > > that > >> > > > > > >> actually > >> > > > > > >> > > > makes > >> > > > > > >> > > > > > use > >> > > > > > >> > > > > > > > >> of > >> > > > > > >> > > > > > > > >>>>>>> offsets.topic.compression.codec: > >> > > > > > >> > > > > > > > >>>>>> > >> https://github.com/apache/kafka/pull/1394 > >> > > > > > >> > > > > > > > >>>>>>> - around 3000 topics. This is an > actual > >> > > subset > >> > > > > of > >> > > > > > >> > topics > >> > > > > > >> > > > from > >> > > > > > >> > > > > > one > >> > > > > > >> > > > > > > > >>> of > >> > > > > > >> > > > > > > > >>>>> our > >> > > > > > >> > > > > > > > >>>>>>> clusters. > >> > > > > > >> > > > > > > > >>>>>>> - topics have 8 partitions > >> > > > > > >> > > > > > > > >>>>>>> - topics are 25 characters long on > >> average > >> > > > > > >> > > > > > > > >>>>>>> - one group with a varying number of > >> > > consumers > >> > > > > > each > >> > > > > > >> > > > hardcoded > >> > > > > > >> > > > > > > > >> with > >> > > > > > >> > > > > > > > >>>> all > >> > > > > > >> > > > > > > > >>>>>> the > >> > > > > > >> > > > > > > > >>>>>>> topics just to make the tests more > >> > > consistent. > >> > > > > > >> > > wildcarding > >> > > > > > >> > > > > with > >> > > > > > >> > > > > > > > >> .* > >> > > > > > >> > > > > > > > >>>>> should > >> > > > > > >> > > > > > > > >>>>>>> have the same effect once the > >> subscription > >> > > > hits > >> > > > > > the > >> > > > > > >> > > > > coordinator > >> > > > > > >> > > > > > > > >> as > >> > > > > > >> > > > > > > > >>>> the > >> > > > > > >> > > > > > > > >>>>>>> subscription has already been fully > >> > expanded > >> > > > out > >> > > > > > to > >> > > > > > >> the > >> > > > > > >> > > > list > >> > > > > > >> > > > > of > >> > > > > > >> > > > > > > > >>>> topics > >> > > > > > >> > > > > > > > >>>>> by > >> > > > > > >> > > > > > > > >>>>>>> the consumers. > >> > > > > > >> > > > > > > > >>>>>>> - I added some log messages to > >> Log.scala > >> > to > >> > > > > print > >> > > > > > >> out > >> > > > > > >> > the > >> > > > > > >> > > > > > message > >> > > > > > >> > > > > > > > >>>> sizes > >> > > > > > >> > > > > > > > >>>>>>> after compression > >> > > > > > >> > > > > > > > >>>>>>> - there are no producers at all and > >> auto > >> > > > commits > >> > > > > > are > >> > > > > > >> > > > > disabled. > >> > > > > > >> > > > > > > > >> The > >> > > > > > >> > > > > > > > >>>> only > >> > > > > > >> > > > > > > > >>>>>>> topic with messages getting added is > >> the > >> > > > > > >> > > __consumer_offsets > >> > > > > > >> > > > > > topic > >> > > > > > >> > > > > > > > >>> and > >> > > > > > >> > > > > > > > >>>>>>> they're only from storing group > >> metadata > >> > > while > >> > > > > > >> > processing > >> > > > > > >> > > > > > > > >>>>>>> SyncGroupRequests. > >> > > > > > >> > > > > > > > >>>>>>> > >> > > > > > >> > > > > > > > >>>>>>> Results: > >> > > > > > >> > > > > > > > >>>>>>> The results below show that we exceed > >> the > >> > > > > 1000012 > >> > > > > > >> byte > >> > > > > > >> > > > > > > > >>>>>>> KafkaConfig.messageMaxBytes limit > >> > relatively > >> > > > > > quickly > >> > > > > > >> > > > (between > >> > > > > > >> > > > > > > > >> 30-40 > >> > > > > > >> > > > > > > > >>>>>>> consumers): > >> > > > > > >> > > > > > > > >>>>>>> 1 consumer 54739 bytes > >> > > > > > >> > > > > > > > >>>>>>> 5 consumers 261524 bytes > >> > > > > > >> > > > > > > > >>>>>>> 10 consumers 459804 bytes > >> > > > > > >> > > > > > > > >>>>>>> 20 consumers 702499 bytes > >> > > > > > >> > > > > > > > >>>>>>> 30 consumers 930525 bytes > >> > > > > > >> > > > > > > > >>>>>>> 40 consumers 1115657 bytes * the > >> tipping > >> > > point > >> > > > > > >> > > > > > > > >>>>>>> 50 consumers 1363112 bytes > >> > > > > > >> > > > > > > > >>>>>>> 60 consumers 1598621 bytes > >> > > > > > >> > > > > > > > >>>>>>> 70 consumers 1837359 bytes > >> > > > > > >> > > > > > > > >>>>>>> 80 consumers 2066934 bytes > >> > > > > > >> > > > > > > > >>>>>>> 90 consumers 2310970 bytes > >> > > > > > >> > > > > > > > >>>>>>> 100 consumers 2542735 bytes > >> > > > > > >> > > > > > > > >>>>>>> > >> > > > > > >> > > > > > > > >>>>>>> Note that the growth itself is pretty > >> > > gradual. > >> > > > > > >> Plotting > >> > > > > > >> > > the > >> > > > > > >> > > > > > > > >> points > >> > > > > > >> > > > > > > > >>>>> makes > >> > > > > > >> > > > > > > > >>>>>> it > >> > > > > > >> > > > > > > > >>>>>>> look roughly linear w.r.t the number > of > >> > > > > consumers: > >> > > > > > >> > > > > > > > >>>>>>> > >> > > > > > >> > > > > > > > >>>>>>> > >> > > > > > >> > > > > > > > >>>>>> > >> > > > > > >> > > > > > > > >>>>> > >> > > > > > >> > > > > > > > >>>> > >> > > > > > >> > > > > > > > >>> > >> > > > > > >> > > > > > > > >> > >> > > > > > >> > > > > > > > > >> > > > > > >> > > > > > > > >> > > > > > >> > > > > > > >> > > > > > >> > > > > > >> > > > > > >> > > > > >> > > > > > >> > > > >> > > > > > >> > > >> > > > > > >> > >> > > > > > > >> > > > > > >> > > > > >> > > > >> > > >> > https://www.wolframalpha.com/input/?i=(1,+54739),+(5,+261524),+(10,+459804),+(20,+702499),+(30,+930525),+(40,+1115657),+(50,+1363112),+(60,+1598621),+(70,+1837359),+(80,+2066934),+(90,+2310970),+(100,+2542735) > >> > > > > > >> > > > > > > > >>>>>>> > >> > > > > > >> > > > > > > > >>>>>>> Also note that these numbers aren't > >> > averages > >> > > > or > >> > > > > > >> medians > >> > > > > > >> > > or > >> > > > > > >> > > > > > > > >> anything > >> > > > > > >> > > > > > > > >>>>> like > >> > > > > > >> > > > > > > > >>>>>>> that. It's just the byte size from a > >> given > >> > > > run. > >> > > > > I > >> > > > > > >> did > >> > > > > > >> > run > >> > > > > > >> > > > > them > >> > > > > > >> > > > > > a > >> > > > > > >> > > > > > > > >>> few > >> > > > > > >> > > > > > > > >>>>>> times > >> > > > > > >> > > > > > > > >>>>>>> and saw similar results. > >> > > > > > >> > > > > > > > >>>>>>> > >> > > > > > >> > > > > > > > >>>>>>> Impact: > >> > > > > > >> > > > > > > > >>>>>>> Even after adding gzip to the > >> > > > __consumer_offsets > >> > > > > > >> topic > >> > > > > > >> > > with > >> > > > > > >> > > > > my > >> > > > > > >> > > > > > > > >>>> pending > >> > > > > > >> > > > > > > > >>>>>>> KAFKA-3718 patch, the AwaitingSync > >> phase > >> > of > >> > > > the > >> > > > > > >> group > >> > > > > > >> > > fails > >> > > > > > >> > > > > > with > >> > > > > > >> > > > > > > > >>>>>>> RecordTooLargeException. This means > the > >> > > > combined > >> > > > > > >> size > >> > > > > > >> > of > >> > > > > > >> > > > each > >> > > > > > >> > > > > > > > >>>> member's > >> > > > > > >> > > > > > > > >>>>>>> subscriptions and assignments > exceeded > >> the > >> > > > > > >> > > > > > > > >>>> KafkaConfig.messageMaxBytes > >> > > > > > >> > > > > > > > >>>>> of > >> > > > > > >> > > > > > > > >>>>>>> 1000012 bytes. The group ends up > dying. > >> > > > > > >> > > > > > > > >>>>>>> > >> > > > > > >> > > > > > > > >>>>>>> Options: > >> > > > > > >> > > > > > > > >>>>>>> 1. Config change: reduce the number > of > >> > > > consumers > >> > > > > > in > >> > > > > > >> the > >> > > > > > >> > > > > group. > >> > > > > > >> > > > > > > > >> This > >> > > > > > >> > > > > > > > >>>>> isn't > >> > > > > > >> > > > > > > > >>>>>>> always a realistic answer in more > >> > strenuous > >> > > > use > >> > > > > > >> cases > >> > > > > > >> > > like > >> > > > > > >> > > > > > > > >>>> MirrorMaker > >> > > > > > >> > > > > > > > >>>>>>> clusters or for auditing. > >> > > > > > >> > > > > > > > >>>>>>> 2. Config change: split the group > into > >> > > smaller > >> > > > > > >> groups > >> > > > > > >> > > which > >> > > > > > >> > > > > > > > >>> together > >> > > > > > >> > > > > > > > >>>>> will > >> > > > > > >> > > > > > > > >>>>>>> get full coverage of the topics. This > >> > gives > >> > > > each > >> > > > > > >> group > >> > > > > > >> > > > > member a > >> > > > > > >> > > > > > > > >>>> smaller > >> > > > > > >> > > > > > > > >>>>>>> subscription.(ex: g1 has topics > >> starting > >> > > with > >> > > > > a-m > >> > > > > > >> while > >> > > > > > >> > > g2 > >> > > > > > >> > > > > has > >> > > > > > >> > > > > > > > >>> topics > >> > > > > > >> > > > > > > > >>>>>>> starting ith n-z). This would be > >> > > operationally > >> > > > > > >> painful > >> > > > > > >> > to > >> > > > > > >> > > > > > manage. > >> > > > > > >> > > > > > > > >>>>>>> 3. Config change: split the topics > >> among > >> > > > members > >> > > > > > of > >> > > > > > >> the > >> > > > > > >> > > > > group. > >> > > > > > >> > > > > > > > >>> Again > >> > > > > > >> > > > > > > > >>>>> this > >> > > > > > >> > > > > > > > >>>>>>> gives each group member a smaller > >> > > > subscription. > >> > > > > > This > >> > > > > > >> > > would > >> > > > > > >> > > > > also > >> > > > > > >> > > > > > > > >> be > >> > > > > > >> > > > > > > > >>>>>>> operationally painful to manage. > >> > > > > > >> > > > > > > > >>>>>>> 4. Config change: bump up > >> > > > > > >> KafkaConfig.messageMaxBytes > >> > > > > > >> > (a > >> > > > > > >> > > > > > > > >>> topic-level > >> > > > > > >> > > > > > > > >>>>>>> config) and > >> > KafkaConfig.replicaFetchMaxBytes > >> > > > (a > >> > > > > > >> > > > broker-level > >> > > > > > >> > > > > > > > >>> config). > >> > > > > > >> > > > > > > > >>>>>>> Applying messageMaxBytes to just the > >> > > > > > >> __consumer_offsets > >> > > > > > >> > > > topic > >> > > > > > >> > > > > > > > >> seems > >> > > > > > >> > > > > > > > >>>>>>> relatively harmless, but bumping up > the > >> > > > > > broker-level > >> > > > > > >> > > > > > > > >>>>> replicaFetchMaxBytes > >> > > > > > >> > > > > > > > >>>>>>> would probably need more attention. > >> > > > > > >> > > > > > > > >>>>>>> 5. Config change: try different > >> > compression > >> > > > > > codecs. > >> > > > > > >> > Based > >> > > > > > >> > > > on > >> > > > > > >> > > > > 2 > >> > > > > > >> > > > > > > > >>>> minutes > >> > > > > > >> > > > > > > > >>>>> of > >> > > > > > >> > > > > > > > >>>>>>> googling, it seems like lz4 and > snappy > >> are > >> > > > > faster > >> > > > > > >> than > >> > > > > > >> > > gzip > >> > > > > > >> > > > > but > >> > > > > > >> > > > > > > > >>> have > >> > > > > > >> > > > > > > > >>>>>> worse > >> > > > > > >> > > > > > > > >>>>>>> compression, so this probably won't > >> help. > >> > > > > > >> > > > > > > > >>>>>>> 6. Implementation change: support > >> sending > >> > > the > >> > > > > > regex > >> > > > > > >> > over > >> > > > > > >> > > > the > >> > > > > > >> > > > > > wire > >> > > > > > >> > > > > > > > >>>>> instead > >> > > > > > >> > > > > > > > >>>>>>> of the fully expanded topic > >> > subscriptions. I > >> > > > > think > >> > > > > > >> > people > >> > > > > > >> > > > > said > >> > > > > > >> > > > > > in > >> > > > > > >> > > > > > > > >>> the > >> > > > > > >> > > > > > > > >>>>>> past > >> > > > > > >> > > > > > > > >>>>>>> that different languages have subtle > >> > > > differences > >> > > > > > in > >> > > > > > >> > > regex, > >> > > > > > >> > > > so > >> > > > > > >> > > > > > > > >> this > >> > > > > > >> > > > > > > > >>>>>> doesn't > >> > > > > > >> > > > > > > > >>>>>>> play nicely with cross-language > groups. > >> > > > > > >> > > > > > > > >>>>>>> 7. Implementation change: maybe we > can > >> > > reverse > >> > > > > the > >> > > > > > >> > > mapping? > >> > > > > > >> > > > > > > > >> Instead > >> > > > > > >> > > > > > > > >>>> of > >> > > > > > >> > > > > > > > >>>>>>> mapping from member to subscriptions, > >> we > >> > can > >> > > > > map a > >> > > > > > >> > > > > subscription > >> > > > > > >> > > > > > > > >> to > >> > > > > > >> > > > > > > > >>> a > >> > > > > > >> > > > > > > > >>>>> list > >> > > > > > >> > > > > > > > >>>>>>> of members. > >> > > > > > >> > > > > > > > >>>>>>> 8. Implementation change: maybe we > can > >> try > >> > > to > >> > > > > > break > >> > > > > > >> > apart > >> > > > > > >> > > > the > >> > > > > > >> > > > > > > > >>>>>> subscription > >> > > > > > >> > > > > > > > >>>>>>> and assignments from the same > >> > > SyncGroupRequest > >> > > > > > into > >> > > > > > >> > > > multiple > >> > > > > > >> > > > > > > > >>> records? > >> > > > > > >> > > > > > > > >>>>>> They > >> > > > > > >> > > > > > > > >>>>>>> can still go to the same message set > >> and > >> > get > >> > > > > > >> appended > >> > > > > > >> > > > > together. > >> > > > > > >> > > > > > > > >>> This > >> > > > > > >> > > > > > > > >>>>> way > >> > > > > > >> > > > > > > > >>>>>>> the limit become the segment size, > >> which > >> > > > > shouldn't > >> > > > > > >> be a > >> > > > > > >> > > > > > problem. > >> > > > > > >> > > > > > > > >>> This > >> > > > > > >> > > > > > > > >>>>> can > >> > > > > > >> > > > > > > > >>>>>>> be tricky to get right because we're > >> > > currently > >> > > > > > >> keying > >> > > > > > >> > > these > >> > > > > > >> > > > > > > > >>> messages > >> > > > > > >> > > > > > > > >>>> on > >> > > > > > >> > > > > > > > >>>>>> the > >> > > > > > >> > > > > > > > >>>>>>> group, so I think records from the > same > >> > > > > rebalance > >> > > > > > >> might > >> > > > > > >> > > > > > > > >>> accidentally > >> > > > > > >> > > > > > > > >>>>>>> compact one another, but my > >> understanding > >> > of > >> > > > > > >> compaction > >> > > > > > >> > > > isn't > >> > > > > > >> > > > > > > > >> that > >> > > > > > >> > > > > > > > >>>>> great. > >> > > > > > >> > > > > > > > >>>>>>> > >> > > > > > >> > > > > > > > >>>>>>> Todo: > >> > > > > > >> > > > > > > > >>>>>>> It would be interesting to rerun the > >> tests > >> > > > with > >> > > > > no > >> > > > > > >> > > > > compression > >> > > > > > >> > > > > > > > >> just > >> > > > > > >> > > > > > > > >>>> to > >> > > > > > >> > > > > > > > >>>>>> see > >> > > > > > >> > > > > > > > >>>>>>> how much gzip is helping but it's > >> getting > >> > > > late. > >> > > > > > >> Maybe > >> > > > > > >> > > > > tomorrow? > >> > > > > > >> > > > > > > > >>>>>>> > >> > > > > > >> > > > > > > > >>>>>>> - Onur > >> > > > > > >> > > > > > > > >>>>>>> > >> > > > > > >> > > > > > > > >>>>>> > >> > > > > > >> > > > > > > > >>>>> > >> > > > > > >> > > > > > > > >>>> > >> > > > > > >> > > > > > > > >>>> > >> > > > > > >> > > > > > > > >>>> > >> > > > > > >> > > > > > > > >>>> -- > >> > > > > > >> > > > > > > > >>>> -- Guozhang > >> > > > > > >> > > > > > > > >>>> > >> > > > > > >> > > > > > > > >>> > >> > > > > > >> > > > > > > > >> > >> > > > > > >> > > > > > > > >> > >> > > > > > >> > > > > > > > >> > >> > > > > > >> > > > > > > > >> -- > >> > > > > > >> > > > > > > > >> -- Guozhang > >> > > > > > >> > > > > > > > >> > >> > > > > > >> > > > > > > > > >> > > > > > >> > > > > > > > > >> > > > > > >> > > > > > > > >> > > > > > >> > > > > > > >> > > > > > >> > > > > > >> > > > > > >> > > > > >> > > > > > >> > > > >> > > > > > >> > > >> > > > > > >> > > >> > > > > > >> > > >> > > > > > >> > -- > >> > > > > > >> > -- Guozhang > >> > > > > > >> > > >> > > > > > >> > >> > > > > > > > >> > > > > > > > >> > > > > > > >> > > > > > >> > > > > >> > > > >> > > >> > > > > >
