Comment by planckscnst | Hacker News Reader

Comment by planckscnst | Hacker News Reader

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> Scylla works within different AZs too

Did your test use this feature of Scylla? As I understand the documentation, it doesn't appear so (maybe that needs to be fixed). If that's the case, do you think this is an example of being diligent in your fairness?

> Only a decrease in the rate solved it.

I don't think that is the only way to solve it. Something is probably wrong here, and I would expect that diligence to fairness would dictate trying to understand and correct that. This benchmark would be more compelling if problems like this weren't just ignored, but actually solved. Any team that cares about the cost of their database would do that.

> It isn't optimal for Dynamo but that's life.

Yes, life is unfair and this can happen. This test specifically claimed to be fair, though. Again, for this benchmark to be meaningful and compelling, this kind of thing should be addressed.

> The only use case where Dynamo is better in price is when you store lots of data but with a tiny IOPS reservation

This is a surprising statement. If this is the case, I highly recommend addressing the issues so that you are using DynamoDB like a typical engineering team would. A blanket statement like this with questionable benchmarks as evidence is just not compelling. It would be much more helpful to see where DynamoDB really can't stand a chance competing against ScyllaDB even when it's fully optimiized.

Are you ignoring maintenance costs? Do nodes get added and removed without paying an engineer? How do you keep the nodes up-to-date as far as security updates or adding new features? How much overhead cost is engineering on-call to respond when the cluster has issues (e.g. nearing capacity limits, nodes failing, loss of AZ availability)?

I'm also curious if you are only considering use cases that you typically already see on ScyllaDB and Cassandra. How about the use case where I have a load that increases without warning by 10x or where I need regular backups or that requires 5000 nodes?

> "...or that requires 5000 nodes?"

While there are indeed deployments that large, I've yet to see a 5,000 node _benchmark_. Though if you've seen tests that big, please send me the link!

That comment was specifically in regards to the claim that ScyllaDB is cheaper for nearly every use case. The 5000 nodes point was to make clear that you cannot disregard automation and maintenance costs. This is relevant to the post's claim about trying to be fair: the operation costs are included in the DynamoDB pricing and not in the ScyllaDB pricing and it was not even mentioned.

Though Amazon's managed service isn't completely managed at that scale either. There are still hot key partitions. There are still other issues that cause people to abandon DynamoDB at scale. And people still have "the blindfold on." q.v.,

https://read.acloud.guru/why-amazon-dynamodb-isnt-for-everyo...

This article is already pretty outdated. According to Jim Scharf with DynamoDB On-Demand you don't really have to care anymore about DynamoDB's implementation details, like partitioning: https://twitter.com/jim_scharf/status/1069056907686465537

There are tons of limitation on the on-demand, certainly it cannot go to extent of 120k ops. Check their example, they toy with a tiny workload.

As far as I know there is no upper limit of requests for DynamoDB. There is a default limit of 40.000 requests per second for provisioned capacity as well as for on-demand capacity, but you can get that increased upon request. See https://docs.aws.amazon.com/amazondynamodb/latest/developerg...

You might also want to read about the scaling behavior of DynamoDB On-Demand (https://docs.aws.amazon.com/amazondynamodb/latest/developerg...). Of course you can't immediately scale to any arbitrary request rate, but the way it's implemented sounds fine to me.

So do you have a source for your claim?

My claim is only an assumption. However, after our experience with not reaching the reserve limit plus the example they provided that didn't scale to a million of iops lead my to this guesstimate. We on the other hand have plenty of examples how to reach a million iops per server with a simple data model. But ignore me, just give Scylla a try! Our support is awesome too

It's not reasonable as a competing/cooperating vendor to claim that there are "tons of limitations" on DynamoDB on demand, and then in the next sentence disclaim it saying your previous assertion was "only an assumption."

Good to know!

About multiple AZ, I think we haven't used it in this case but it shouldn't change a bit, most of our AWS customers have AZ-aware deployments and it works great.

Since I see you're with AWS, you're welcome to help us debug this error 500 on population. I guarantee we'll update the blog if we'll see it works fine

I didn't get your surprise, I actually am 100% open about digging deep and come up with a uncommon use case that Dynamo can finally be a good alternative.

Believe me, I can come with examples that will put Scylla in a much better light.

We do offer a fully managed service on AWS with 4x-6x cost saving vs Dynamo where all the backup and auto scale is done by the Scylla team.

> About multiple AZ, I think we haven't used it in this case but it shouldn't change a bit

Are you suggesting that the metrics would not change? I assure you that is not the case: inter-AZ latency is 1-2 orders of magnitude higher than intra-AZ latency.

You'll need to re-run your benchmarks in a multi-AZ cluster in order to provide an apples-to-apples comparison.

I don't think this is the case - check this link: https://knowledgebase.progress.com/articles/Article/expected...

The intra AZ latency according to AWS is sub millisecond! It's inline with what our customers see.

Since all of the numbers in the blog are above a millisecond, the result does not change.

Intra-AZ latency is indeed sub-millisecond. Inter-AZ latency is in the milliseconds range. (The intra prefix means within, inter means between.) And those latencies accumulate quickly when benchmarking.

Why don't you try it yourself and see the difference? Relying on some third party website is no substitute for testing.

I went and run a ping between 2 VMs, one on us-east1c and the other on a different AZ - us-east-1b

As you can see, the ping latency is 0.5ms to 1ms on rare occasions. Of course that ping has a cost even within a single AZ so the above numbers reflect much more than the AZ round trip time.

You're welcome to add 1ms to our latency numbers, it's 3x-4x better in the 99th case so there's enough room...

64 bytes from 35.173.249.24: icmp_seq=14 ttl=63 time=0.584 ms 64 bytes from 35.173.249.24: icmp_seq=15 ttl=63 time=0.462 ms 64 bytes from 35.173.249.24: icmp_seq=16 ttl=63 time=0.848 ms 64 bytes from 35.173.249.24: icmp_seq=17 ttl=63 time=0.465 ms 64 bytes from 35.173.249.24: icmp_seq=18 ttl=63 time=0.451 ms 64 bytes from 35.173.249.24: icmp_seq=19 ttl=63 time=1.00 ms 64 bytes from 35.173.249.24: icmp_seq=20 ttl=63 time=0.854 ms 64 bytes from 35.173.249.24: icmp_seq=21 ttl=63 time=0.446 ms

Inter-AZ latency is going to matter more for conditional writes. I'm disappointed to find LWT so far out on Scylla's roadmap since preventing conflicts is a showstopper for correctness and we found it to be Cassandra's weak point in scaling.

fwiw, work being done on Cassandra to speed this (cas/lwt) up SIGNIFICANTLY

Link ?

Started here: https://lists.apache.org/thread.html/15d1b4b5bb8a24e41d51db5...

Continues here: https://issues.apache.org/jira/browse/CASSANDRA-14448

Quorum reads will always be much faster in the same AZ :-(

> you're welcome to help us debug this error 500 on population

Create the table with 4x the provisioned capacity and then dial down to your nominal levels after it's been created.

Are you serious? Or is my sarcasm meter faulty?

So you solve 500 errors by provisioning 4x your usage? Seems like solving a leak in the gas tank by instructing the user to simply fill up the tank more often.

Nice business if you are the gas station!

This is a kludgy way to get DynamoDB to leave your table split across more shards, even after you dial it down to the capacity you need.

It may work at the price of 4x which is already 7x higher, resulting in 28x total.. not to mention the hassle. Man, give us a try.

Seen your comment about LWT, agree.. We knownly chose the first make MV/SI great before committing to another big feature. Glad to say that with Scylla 3.0 release this month we'll finally get LWT done

It's a price of 4x higher for just long enough to create the table, not for the duration of the test.

> Are you serious?

They really are. In order to make effective (let alone efficient) use of DynamoDB you need to keep in mind exactly how it works behind-the-scenes and exactly how the charging models works at all times. And you have very few, very coarse levers to pull (over-provision, under-provision, etc.)

Every in-depth explanation or tutorial of DynamoDB I've seen advises to do things like this in multiple different load scenarios. There's a pretty good intro for DynamoDB over at acloud.guru: https://acloud.guru/learn/aws-dynamodb - beware though, it costs money and it's very long (though it's split up so you can cherry pick the bits you care about).

I think DynamoDB might be worth investigating when you're hitting a scale where most other off-the-shelf options don't work and you'd be heading down the path of building your own solution on top of something anyway.

I'd just point out Scylla tries to auto-tune itself, so you don't need to know about or perform such dark arcana just to get it working out-of-the-box. I mean, I get it. Databases are hard. But this is a hidden gotcha that you should not have to pay through the nose (in time or money) to learn to avoid.

When you are hitting a real scale, DynamoDB becomes prohibitively expensive.

What was your own experience like?

We run a lot on aws. Services, databases, ... Cassandra, Aerosoike, Couchbase, DynamoDB to name a few. Each of them is good in something, but DynamoDB is the most expensive one. For small datasets with low RPS it provides a lot of value, but once you scale, it becomes cheaper to run ouselves (even including licensing costs). I blame their linear pricing model.

Thanks for the feedback, LaserToy!

The suggestion was to provision it at 4x, then dial back down to 1x, then load the data. This is to force DynamoDB to split the partitions further before you use them so that they don't split while you're filling the table.

> Believe me, I can come with examples that will put Scylla in a much better light

I know this; it's why I was disappointed in the way this test was designed. It would be great to see as close as possible comparison between the two then mention improvements and trade-offs that you can still make (such as single-AZ or self-service) since you have different knobs to turn as well as DynamoDB quirks (such as item size boundaries) that can make ScyllaDB more attractive for your use-case.

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