I made the mistake of asking two things in one email. First thing I asked. Sidecar? Stalled CEP so why is this being talked about like this is a thing?
On Mon, Sep 30, 2024 at 7:21 AM Benedict <bened...@apache.org> wrote: > Sorry Bernardo, you may have misunderstood me. I don’t have any concerns, > I was suggesting a possible future scenario where CDC for Kafka via sidecar > is changed to use a hypothetical future topic subscription service provided > by C*. It was meant to show that this CEP may be easily decoupled from any > future evolution in this area. > > On 30 Sep 2024, at 14:58, Bernardo Botella <conta...@bernardobotella.com> > wrote: > > Thanks everyone for the comments. > > > Patrick: > The proposal includes a “best effort” approach for deduplication (some > details can be found on the Digest class comments on the PR here > https://github.com/apache/cassandra-analytics/pull/87/files#diff-3a09caecc1da13419d92cde56a7cfc7d253faac08182e6c2768b3d32c015de82R185-R193 > ). > That alone won’t eliminate all the duplicates, but as Josh points out, it > moves the line to something way easier to handle for consumers, and > definitely on the direction we should aim towards. Accord is definitely > something this contribution will benefit from, that will move that line > even further. > > Benedict: > If I understand it correctly, your concern is that Kafka is somewhat the > hardcoded option for a CDC stream being published? The proposal introduces > a concept of data sources and sinks ( > https://cwiki.apache.org/confluence/pages/viewpage.action?pageId=323488575#CEP44:KafkaintegrationforCassandraCDCusingSidecar-SourcesandSinks) > being kafka the first implemented data sink. That means that the actual > Kafka output should (will) be something pluggable. > > > > On Sep 30, 2024, at 5:43 AM, Josh McKenzie <jmcken...@apache.org> wrote: > > I don't see much on how this would be handled other than "left to the end > user to figure out." > > My immediate thought when I read that was "Yes. But it's moving where we > draw the line of 'left to the end user to figure out' *much further* than > it was before". > > This should only be necessary in edge cases w/extended severe degraded > availability where you can't hit QUORUM w/this design. So we go from > "De-dupe literally everything o ye' user" to "de-dupe a small fraction of a > % of the time when things really go off the rails". > > It still leaves the burden of processing potential duplicates downstream, > so some *complexity* burden on the users remains if they have no > tolerance for processing duplicate messages, however the underlying machine > resource utilization (from "dedupe everything" to "dedupe a small % of > things") is pretty massively shifted by this design change. That, and using > the hash of the mutation the way the extended design does is something a > downstream consumer could also do on their side to ensure anything that > came in past the drop-off window wasn't already seen. So not *too* painful; > certainly a vast improvement over the status quo. > > As to TCM and Accord: absolutely agree. I'd love to see a world where we > Accord everything and fire off CDC to subscribers from a coordinator > bypassing all this LSM-bastardized post-processing for CDC for instance. > That said, this is a functionality users needed back in... 2016? When we > first added CDC. So I think it's worth it to move on it now while retaining > architectural options to move to updated metadata and transactions as they > mature (obviously we'll lean on TCM since it's in 5.0 / trunk right now; > more applies to the accord bit). > > On Mon, Sep 30, 2024, at 3:20 AM, Benedict wrote: > > > Yes, with accord it should be fairly easy to have reliable no-dupe log > streaming without an elected leader. Given the broad set of use cases, I > can imagine supporting some more native topic subscription API in C* rather > than requiring Kafka, so perhaps any integration of Kafka with the sidecar > can be considered a separate parallel effort, that might eventually > implement itself with this C* feature whenever it materialises? > > > On 30 Sep 2024, at 03:42, Jeff Jirsa <jji...@gmail.com> wrote: > > > > Transactional metadata and Accord should make it MUCH easier to do > duplication avoiding CDC (and I was going to note that someone should > ensure that the interfaces exposed to the public are stable enough not to > change the published api once those exist) > > > > On Sep 29, 2024, at 7:04 PM, Patrick McFadin <pmcfa...@gmail.com> wrote: > > > As I was reviewing this, it occurred to me that it was talking about > Sidecar like it was a thing but that CEP has been stalled for quite some > time: > https://cwiki.apache.org/confluence/pages/viewpage.action?pageId=95652224 > > If work on this is being done, should we get this official and wrapped up? > > On to the proposal... > > This has been a topic on the project for over 10 years now. I've seen > multiple goes at making this work and the issue that always turns out to > torpedo the project is handing dupes. To the point that they go from a > generalized Kafka producer engine to something specific to a particular use > case. I don't see much on how this would be handled other than "left to the > end user to figure out." > > There is also little mention of where the increased resource load would be > handled. > > This has been discussed many times before, but is it time to introduce the > concept of an elected leader for a token range for this type of operation? > It would eliminate a ton of problems that need to managed when bridging c* > to a system like Kafka. Last time it was discussed in earnest was for > KIP-30: > https://cwiki.apache.org/confluence/display/KAFKA/KIP-30+-+Allow+for+brokers+to+have+plug-able+consensus+and+meta+data+storage+sub+systems > > > Patrick > > On Sat, Sep 28, 2024 at 11:44 AM Jon Haddad <j...@rustyrazorblade.com> > wrote: > > Yes! I’m really looking forward to trying this out. The CEP looks really > well thought out. I think this will make CDC a lot more useful for a lot of > teams. > Jon > > > On Fri, Sep 27, 2024 at 4:23 PM Josh McKenzie <jmcken...@apache.org> > wrote: > > > Really excited to see this hit the ML James. > > As author of the base CDC (get your stones ready for throwing :D) and > someone moderately involved in the CEP here, definitely welcome any > questions. CDC is a *thorny* *problem *in a multi-replica distributed > system like this. > > On Fri, Sep 27, 2024, at 5:40 PM, James Berragan wrote: > > Hi everyone, > > Wiki: > https://cwiki.apache.org/confluence/display/CASSANDRA/CEP-44%3A+Kafka+integration+for+Cassandra+CDC+using+Sidecar > > We would like to propose this CEP for adoption by the community. > > CDC is a common technique in databases but right now there is no > out-of-the-box solution to do this easily and at scale with Cassandra. Our > proposal is to build a fully-fledged solution into the Apache Cassandra > Sidecar. This comes with a number of benefits: > - Sidecar is an official part of the existing Cassandra eco-system. > - Sidecar runs co-located with Cassandra instances and so scales with the > cluster size. > - Sidecar can access the underlying Cassandra database to store CDC > configuration and the CDC state in a special table. > - Running in the Sidecar does not require additional external resources to > run. > > The core CDC module we anticipate will be pluggable and re-usable, it is > available for review here: > https://github.com/apache/cassandra-analytics/pull/87. The remaining > Sidecar code will follow. > > As a reminder, please keep the discussion here on the dev list vs. in the > wiki, as we’ve found it easier to manage via email. > > Sincerely, > James Berragan > Bernardo Botella Corbi > Yifan Cai > Jyothsna Konisa > > >
