15 ms·
MemoryDB: A fast and durable memory-first cloud database
- flanked-evergl 3y agoMemoryDB launched in 2021.
- richwater 3y agoYes, that's why the abstract says that.
- eatonphil 3y agoLink to the paper [0]. Interesting stuff. > This paper presents Amazon MemoryDB, a fast and durable inmemory storage cloud-based service. A core design behind MemoryDB is to decouple durability from the in-memory execution engine by leveraging an internal AWS transaction log service. In doing so, MemoryDB is able to separate consistency and durability concerns away from the engine allowing to independently scale performance and availability. To achieve that, a key challenge was ensuring strong consistency across all failure modes while maintaining the performance and full compatibility with Redis. MemoryDB solves this by intercepting the Redis replication stream, redirecting it to the transaction log, and converting it into synchronous replication. MemoryDB built a leadership mechanism atop the transaction log which enforces strong consistency. MemoryDB unlocks new capabilities for customers that do not want to trade consistency or performance while using Redis API, one of the most popular data stores of the past decade. [0] https://assets.amazon.science/e0/1b/ba6c28034babbc1b18f54aa8102e/amazon-memorydb-a-fast-and-durable-memory-first-cloud-database.pdf https://assets.amazon.science/e0/1b/ba6c28034babbc1b18f54aa8...
- vlovich123 3y agoI don’t get this part: > MemoryDB solves this by intercepting the Redis replication stream, redirecting it to the transaction log, and converting it into synchronous replication Replication is eventually consistent in Redis - is it saying that it’s intercepting the stream at the source and blocking the write from completing until replication completes? Cause intercepting it at the point it’s going out (which is what the word interception implies to me) wouldn’t get you strong consistency I would think.
- alucard055 3y agofrom sec 3.2 in the paper "Due to our choice of using passive replication, mutations are executed on a primary node before being committed into the trans- action log. If a commit fails, for example due to network isolation, the change must not be acknowledged and must not become visible. Other database engines use isolation mechanisms like Multi-Version Concurrency Control (MVCC) to achieve this, but Redis data struc- tures do not support this functionality, and it cannot be readily decoupled from the database engine itself. Instead, MemoryDB adds a layer of client blocking. After a client sends a mutation, the reply from the mutation operation is stored in a tracker until the transaction log acknowledges persistence and only then sent to the client. Meanwhile, the Redis workloop can process other operations. Non-mutating operations can be executed immediately but must consult the tracker to determine if their results must also be delayed until a particular log write completes. Hazards are detected at the key level. If the value or data-structure in a key has been modified by an operation which is not yet persisted, the responses to read operations on that key are delayed until all data in that response is persisted. Replica nodes do not require blocking as mutations are only visible once committed to three AZs"
- convolvatron 3y agothis is kind of a strange design. in order to support this we build an external model of the database for all potentially conflicting state. wouldn't it be easier to make a redis lookalike that supported high isolation levels?
- jitl 3y agoThe external model is much simpler to do for Redis than a database with complex cross-key queries like an SQL database. Redis has scans but no queries or “real” transactions with rollback. To me it sounds like more work to implement MemoryDB and then additionally re-implement the Redis interior than to implement MemoryDB and use the off-the-shelf Redis. I also think that the decoupled design is kind of elegant, it allows the logical implementation to be developed independently of the durability bits. It’s open-core but someone else is building the core.
- vasco 3y agoWe've used it at work for a specific use case where paying for a more expensive redis that survives downtime with no frills made sense. It's quite expensive but super easy to use.
- refset 3y agoConsidering the functionality on offer the service does look particularly easy to work with, even though there's still a notion of a stateful cluster with per-node sizing & pricing. Perhaps the MemoryDB team will offer something more 'serverless' eventually.
- klaussilveira 3y agoThe fact that there's no source anywhere shows how important GPL is. What use is this to the rest of the community?
- abigail95 3y agoI don't care about the source code of anything Amazon runs. The source code doesn't get me 11 9's. That's what people are paying for. Why is the community better off without this option?
- refset 3y agoAnything that helps turn RESP into more of a commodity protocol seems like a good thing in the long run. It seems to be simple enough that workloads can legitimately migrate around and users can vote with their wallets for whoever operates the most secure/available/portable(OSS) platform. By contrast SQL tech is in a far more precarious state.
- shrubble 3y agoSo basically if you can't run it anywhere other than AWS, it's no more newsworthy than talking about a COBOL compiler for an IBM mainframe; which is also equally capable of giving you 11 9's. BTW AWS can't possibly have been delivering on 11 9's given their previous outages; 9 9's is 0.031s over a year.
- markfive 3y agoPedantic clarification incoming: 11 9's is the Durability guarantee for S3. It doesn't refer to Availability.
- anonzzzies 3y agoBut for this memorydb it seems it is? Indeed not for entire AWS either way though.
- 3y ago
- flakiness 3y agoFYI MemoryDB is a Redis compatible managed db. (For someone who's not familiar with AWS offerings) https://aws.amazon.com/memorydb/ https://aws.amazon.com/memorydb/
- supportengineer 3y agoIf we had truly orthogonal systems, you could setup a RAM Disk, and run SQLite with the backing store file in the RAM disk, without any custom software needed at all.
- rmbyrro 3y agoIt depends on a few more factors, no? For instance: it's hard to scale concurrent writes with SQLite. I read they have an enterprise paid version with higher write concurrency support, but have no idea how it works and whether it'd compare with Redis or MemoryDB's write concurrency levels.
- zbentley 3y agoAre you saying durability is "orthogonal" in that it should be managed outside of the database (in your example, perhaps by copying sqlite files to durable storage)? If not, then your proposed design seems pretty different from MemoryDB; yours doesn't persist data in the event of machine loss or reboot.
- spxneo 3y ago> 11 9s of durability so thats 99.(eleven 9s) ? where would this sort of database used? streaming financial instrument ticks? Do you point Kinesis and its able to write/read super quickly?
- random3 3y agoIt's a bit disingenuous to slap 11 9s in the first phrase of something called MemoryDB and drop "durability" after, implied by the otherwise boring durability of S3. This said, it's not bad. I'd keep in mind that the paper is one thing and putting your money where your mouth is means having an SLA for latency. So far, Google's BigTable is the only service with a read latency SLA. - 99.99 availability - 3ms p50 - 6ms P99 read-only! latency
- deanCommie 3y agoSLAs with public cloud providers don't mean what people think they mean (not saying you do, but i bet a lot of other readers do). SLAs just mean "if you can prove that we didn't meet our SLA, we'll give you a refund, and by refund we mean some % of your bill for some duration". It's not nothing - it's obviously $$s, and so teams get measured and have goals about improving their availability and latency. But most customers don't seek out those refunds, and so there is no real pressure connected between the SLA and their true performance (which is often much BETTER than the SLAs, but not because of the SLAs)
- ak217 3y ago> there is no real pressure connected between the SLA and their true performance I'm not sure I understand this. Regardless of the refund, if a provider cuts enough corners with SLAs, won't the customers eventually raise a stink about it and make use of the (thankfully robust) competition? Plus there's the support overhead of tracking the performance and issuing the refund, which might exceed the cost of the refund itself. I think to most people an SLA is an indicator that a company is serious about this aspect of the product's performance. Serious enough to write it into long term contracts and align its incentives to fulfill it.
- broly98 3y agoI don't understand where you got `- 3ms p50 - 6ms P99 read-only! latency ` ? https://cloud.google.com/bigtable/sla https://cloud.google.com/bigtable/sla doesn't refer to any latency SLA.
- dangoodmanUT 3y agoThis feels too high level. They just sort of explain how they are durable via a log (e.g. RedPanda) and store things in mem. It'd be more interesting if they talked about what log they used (Kinesis? Something on another DB?), what did they use for a locking service and how did they handle failure cases, etc.
- dangoodmanUT 3y agoIt also seems like a strange choice to use gossip when they have a shared log
- zxt_tzx 3y agoInteresting stuff. We use MemoryDB as the underlying service for BullMQ, a NodeJS queue that’s built on top of Redis. We trade off a bit of speed and cost (MemoryDB costs more than Elasticache) for persistence and BullMQ’s many features, which is a good tradeoff for most apps.