Bedrock – Rock-solid distributed data

http://bedrockdb.com/

by qertoip • 10 years ago

134 109 10 years ago

bedrockdb.com

partycoder4• 10 years ago

I don't want to be a jerk but... just for the sake of common sense:

- Faster? Provide a benchmark. Faster is a relative thing, faster than what? faster under which conditions?

- More reliable... than what? under which conditions? how do you know it is more reliable?

- More powerful? I thought SQLite is more constrained than other SQL databases. e.g: No stored procedures. Powerful? how? compared to exactly what?

Nullius in verba. I don't take your statements as granted, give me a proof, otherwise it's just flatus vocis.

quinthar45• 10 years ago

Thanks for all that Latin! Yes, it's been open sourced for under 24 hours. Those are all good suggestions.

partycoder4• 10 years ago

Una lingua numquam satis est. Gratias tibi. Good luck with your project.

quinthar45• 10 years ago

Incidentally, sqlite doesn't provide stored procedures, but Bedrock does (using a C++ plugin capability). Otherwise, SQLite is actually very feature rich; a subset of features are here: http://sqlite.org/fullsql.html

partycoder4• 10 years ago

Yes... but you said "More powerful", rather than just "Powerful". More implies a comparison with respect to something else... with what specifically?

sonofgod• 10 years ago

Where do you make your CAP Theorem tradeoffs?

When shouldn't people use Bedrock? https://sqlite.org/whentouse.html is a wonderful page - full of discouragement to would-be SQlite users to know when they're in a use-case better served by some other tool.

quinthar45• 10 years ago

Heh, yep, we definitely had that sent to us. The point of Bedrock is to resolve those points and make SQLite usable in the enterprise.

As for the CAP theorem, we compromise on "C". Each slave responds based on its current state, which might be a different state than other slaves or the master. However, every response returns the "commitCount" of the database at the time the response was generated. Then when you submit a new request, you can specify that commitCount and the slave will wait until it is at least as recent as that.

This way you can safely act upon the response of one request, and then make a second request to another.

thesmallestcat5• 10 years ago

So you're ensuring consistency by blocking on all queries? And it's up to the client to enforce this to any degree? And if there's one master and a global clock, sounds like you threw out the "P" too. Frankly this thing sounds simplistic and unusable, and it's sorta offensive to hear SQLite called unusable in the enterprise, whatever that means.

thesmallestcat5• 10 years ago

You'd have to be nuts to depend on something backed by Expensify. They'll probably fire the maintainers.

Edit: Turns out it's authored by the CEO! So you'd have to be nuts to use it, period. But, um, poke the source if you're curious. This is a good intro https://github.com/Expensify/Bedrock/tree/master/libstuff#li... I can't imagine a more ironic and hilarious backdrop for the "We Fire People" campaign. Must be tough finding people who can keep up with a brain that big.

quinthar45• 10 years ago

Out of curiosity, what specifically do you find idiotic about the document you linked to?

thesmallestcat5• 10 years ago

I didn't call anything idiotic. But let's just say that grappling with the STL may be slightly preferable to this... thing. And there is some special irony referring to STL as an "esoteric abstraction" while offering your own vastly more esoteric abstractions in the same swoop. And the following paragraph speaks for itself, particularly in the context of developing a fucking database:

Computers are super fast these days, and real world applications spend 99% of their CPU time doing some very specific item, with the rest of the time spent doing just boring stuff. Accordingly, libstuff is not intended to be hyper-efficient: it's intended to be hyper-usable. This means libstuff uses a lot of std::string objects for pretty much everything. Where a more complex object is required, some higher-level string-based object is used.

dsl• 10 years ago

For all the emphasis put on multi-datacenter replication, it would be awesome to see it documented!

Really looking forward to playing with this. Cool stuff.

quinthar45• 10 years ago

There's a bit of that here: http://bedrockdb.com/multizone.html

But yes, lots more details to add over time. Thanks for asking!

quinthar45• 10 years ago

And a bit more here: http://bedrockdb.com/synchronization.html

carterehsmith• 10 years ago

Rock-solid?

Look. Just about anyone can create some "database" and declare it "rock-solid". Frankly, a simple key-value store is built in most languages.

Do you have more than that? Do you have benchmarks? You know, competing against the other providers?

thesmallestcat5• 10 years ago

It must be Bedrock Linux' standard DB.

quinthar45• 10 years ago

Agreed, benchmarks would be helpful to back up these claims. Good suggestion!

I think the argument in favor of it being more reliable is an easier one, however, as Bedrock is specifically designed (and used, at scale, for 8 years) to provide highly available redundancy in the form of WAN-replication and automatic failover.

Regardless, I think you'll agree that "rock-solid" is not a precise technical term, and I hope you'll allow a bit of play on words. Whether or not it's literally as solid as a rock is unclear, but it is definitely very reliable -- and more reliable than most.

quinthar45• 10 years ago

Discuss in real-time here: https://gitter.im/Expensify-Bedrock/Lobby

misframer2• 10 years ago

Here's Expensify's CEO (David Barrett) posting on the p2p-hackers mailing list about this. It's from April 2016.

http://p2p-hackers.709552.n3.nabble.com/p2p-hackers-Advice-o...

quinthar45• 10 years ago

Yes, we've made a lot of good progress on this front, though nothing ready to demo. Multi-threaded replication is really exciting stuff. As it stands, our "selective sync" capability already gives a lot of headroom for write capacity, but multi-threaded replication will raise that ceiling even higher.

Jweb_Guru9• 10 years ago

The fundamental issue you're going to run into is that unless you have "genuine partial replication" where only certain shards have a key, or restrict your queries to key/value ones where the key can be determined automatically and used to route to a per-shard master, you can't detect conflicts committed on different nodes without executing half a round trip, which is going to be bottlenecked by the slowest node in your "fast" quorum. That's why nobody uses Generalized Consensus in practice.

Batching before that will help if you already know that most of the transactions touching a particular key are going to the same server. So not a clean partition, but "most of the time". This is the idea behind, e.g., http://www.ssrg.ece.vt.edu/papers/peluso-M2PAXOS-TR.pdf. You try to make sure people usually contact the owner of a particular partition, and use a variety of techniques from the literature to make that well-optimized (ideally, clients actually know which partitions they "should" be accessing, too).

Another approach is to restrict your transactions to deterministic ones (with possible "scouting" transactions to do things like secondary index lookups where you can't statically analyze which partitions they will hit), in which case you can batch all transactions, send them to all participant nodes, and run them afterwards without two-phase commit. This is the approach taken by Calvin (which can exploit per-node parallelism during execution because it uses deterministic, deadlock-free locking). Additionally, read-only transactions scoped to a partition can execute locally without any distributed access, because thanks to determinism serializability is guaranteed. See http://cs-www.cs.yale.edu/homes/dna/papers/calvin-tods14.pdf (and yes, it really can do 500,000 distributed TPC-C transactions per second--by my estimation, more than three orders of magnitude higher than the average total traffic you get, as suggested by your "100x more read transactions than write" estimate. Though of course your current average is higher than your 8-year average, I doubt it is 1000x higher).

Yet another idea is to try to combine coordination required for replication with that required for the distributed transaction, as Tapir does: https://github.com/UWSysLab/tapir. It enjoys the highest linearizable read/write "general" (as in, doesn't have to be submitted in one batch or need static analysis) transaction throughput I've seen of any leaderless georeplicated system (aka it processes transactions "fairly").

Still another approach is to forego serializability for a very slightly weaker guarantee, extended update serializability, which eliminates nearly all interesting anomalies but can allow for dramatically better performance: http://www.ssrg.ece.vt.edu/papers/opodis14-alvin.pdf demonstrates that on read-mostly workloads you can do very well with that even in absurd deployments (e.g. the georeplicated 7 datacenter one in the paper). Elsewhere in the thread you were talking about how "observational" consistency is what's important, which would suggest you are probably already relying on the "strong session" assumption (in which case EUS is indistinguishable from serializability), so I encourage you to give that a look.

All four represent pretty interesting points on the design space. It's not clear to me whether RockSolid would be better than, say, SQLite over Calvin, for your use case (in particular, I suspect Expensify would not find Calvin's requirement that transactions be statically analyzable terribly onerous, especially since you already require all transactions to be executed as stored procedures).

I will say that I'm pleased that a site receiving a reasonable amount of traffic is using SQLite. People consistently underestimate its performance.

hbrundage2• 10 years ago

I don't quite get why SQLite is the right primitive to compose a large scale database system out of...

If the design goal is write throughput, SQLite can be beat really easily by the client/server systems since each SQLite instance only supports one concurrent writer. I guess users of Bedrock could partition their datasets into different pieces that aren't often written in tandem, but why go through all the trouble instead of just using a database with real MVCC?

If the design goal is geo replication, Bedrock seems to ignore the past many years of innovation in the field. MySQL and company have methodically built up features to allow safe synchronous and asynchronous replication for minimizing the risk of downtime or data loss like GTIDs over a long time

If the design goal is read throughput, I don't think Bedrock can be faster than just pure SQLite if your data can live beside your application, and if you have more than one node, you need a complicated SQL optimizer that understands how to push down things like predicates and aggregates to the leaves, and then recombine results at the top level to actually efficiently read in parallel, which I don't think Bedrock has built yet.

This thing kind of seems reminiscent of Jetpants or one of the other MySQL orchestration tools that allow for scaling the DB beyond many nodes automatically... but... why SQLite?

quinthar45• 10 years ago

Thanks for asking!

Re: "SQLite can be beat really easily by the client/server systems since each SQLite instance only supports one concurrent writer" -- That's not actually true, sqlite supports concurrent writers via their page-locking branch (and changesets allow for effectively row-level locks). But none of that matters, because single-threaded replication means any multi-threaded write capability is irrelevant. Regardless, when we add multi-threaded replication (on the way), we'll take advantage of SQLite's multi-thread write capabilities.

Re: MySQL's replication. What specifically are you referring to? It's distributed transaction features are actually quite new -- and I think were developed after Bedrock was already in production for years. Furthermore, MySQL doesn't support automatic master failover (or recovery), and struggles over high-latency, low-reliability WAN connections. Anyway, if I'm wrong on any of that, I'm eager to be corrected. Thanks!

Re: Read throughput. Agreed it doesn't have "parallel reads" (eg, it doesn't split a large read up into multiple smaller reads that are joined automatically). However, I don't think MySQL does either. Regardless, Bedrock does quite well for normal read queries, and uses all of the node's CPUs efficiently. (To be clear, I love this idea of adding "super threaded reads", and have some ideas. But at the moment we don't have any application that requires it, so haven't built it.)

Re: Jetpants, I haven't heard of that before. Thanks for the tip! But as for why SQLite over MySQL, I'd ask quite the opposite: why add a networked layer on top of MySQL, thereby ignoring all of MySQL's networking? That just adds all the overhead of MySQL, without any of the benefit. If you're going to build a networking layer atop a database, SQLite seems the clear choice because it is explicitly designed to be a database library -- and not a database server.

Thanks for all these comments!

chucky_z• 10 years ago

Automatic failover -- https://dev.mysql.com/doc/mysql-utilities/1.5/en/mysqlfailov...

Guides to doing auto failover and recovery:

https://dev.mysql.com/doc/mysql-utilities/1.5/en/utils-task-...

ngrilly10• 10 years ago

sqlite supports concurrent writers via their page-locking branch (and changesets allow for effectively row-level locks)

I've been unable to find the branch on SQLite website. Do you have a link to the branch and changesets?

hbrundage2• 10 years ago

Don't let me barge in and tell you how to do your job or anything, but for a piece of a system designed and marketed as the bottom, super stable piece of the stack, shipping out a brand new technology not yet in trunk seems kind of dangerous, no? The MVCC implementations in your competitors have been battle tested for stability and maximum performance for decades. Gonna be hard to compete with that.

Re: "struggles over high-latency, low-reliability WAN connections" If by struggle you mean a vanilla MySQL replication setup doesn't satisfy C, A and P of the CAP theorem then yeah I agree, however if you just mean that it struggles to be consistent with an unreliable network, that just means MySQL has made the same CAP tradeoff Bedrock has. AFAIK there aren't many critical bugs that mean you lose data that could have otherwise been stored in the presence of unreliable networks.

You're right that vanilla MySQL doesn't support automatic failover, however, some consider that a feature, because the engineering required to correctly implement this distributed system is genuinely challenging. Bedrock may have done it, but if there are some complicated cases that it has yet to address users may prefer to manage failover manually before they trust it to the system. MySQL also isn't the only system that we should draw comparison too -- Cassandra or Riak come to mind as well. Both have excellent replication for geo-redundancy and something akin to automatic failover by storing data in a configurable number of places. They don't support raw SQL statements like Bedrock does, but to be honest if Bedrock doesn't support actual SQL fanout where the results can be combined to make the thing seem like one big database, the client is left to do a bunch of the work like they would be doing in Cassandra to model their data and fetch it efficiently.

I'm not trying to suggest that MySQL or a MySQL orchestration layer is better than Bedrock for all use cases; I just don't understand what niche Bedrock is trying to fill. For basic consumers of the system it's more work to author your queries for Bedrock because (I think) you now have to manage multiple logical SQL instances instead of one virtual big one, and you only get as much read throughput for as much data as you are willing to duplicate. You only get write throughput for the same but at 1 writer per shard/slave/whatever it's called. It's using a homegrown replication algorithm that has the same consistency tradeoffs of other more widely deployed and thus better tested solutions, and it's not clear that database builders or the target audience for Bedrock-as-framework would actually want to use SQLite due to the performance considerations mentioned above.

notacoward• 10 years ago

The idea's not fundamentally bad, but some of the rhetoric raises alarm bells.

built atop SQLite, the fastest, most reliable, and most widely distributed database in the world.

Most widely distributed maybe, but far from the fastest and AFAIK others beat it on reliability as well. No disrespect to SQLite, it's far more feature-rich than other embedded-style DBs, but without a definition of "database" that excludes them the statement as written is false.

written for modern hardware with large SSD-backed RAID drives and generous RAM file caches

In other words, relies on those things so it won't work worth crap on anything less.

The easiest way to talk with Bedrock is using netcat as follows

Nice security model you've got there.

quinthar45• 10 years ago

Re: SQLite's performance -- Can you point to anything that shows SQLite isn't the fastest for some class of query? In my experience (though admittedly I haven't formally benchmarked) it's at least as fast, and generally faster (due to the dramatically reduced overhead to query it over a traditional database server).

Re: SQLite reliability. I'm confused how SQLite isn't more reliable than every other contender, merely given that there is so much less to fail. In 8 years, 2158341079 writes, and probably 100x that many reads, I don't think I've ever had a single failure or bug with SQLite itself.

Re: SSDs -- That's a fair point. Bedrock is not the ideal choice if you are using small volumes and spinning disks.

Re: Security -- I think all databases have crap security that nobody really relies upon. Bedrock doesn't try to pretend. Rather, it gives you a very complete plugin framework, such that you can write C++ "stored procedures" that enforce your application's security model. In practice, we run with the Bedrock::DB plugin disabled, such that the only way to access the database is via our stored procedures -- and those do complete authentication and authorization in an application-specific way that no database could in a generalized fashion.

Thanks for asking!

ngrilly10• 10 years ago

2158341079 writes

I'm curious: how do you keep track of this number?

misframer2• 10 years ago

How do you monitor a database / system like this?

quinthar45• 10 years ago

The Bedrock::Status plugin returns full status on its internal state, as well as the state of the other nodes it sees. We have Icinga monitor this to make sure the serve is not merely up, but in the correct state.

lucio3• 10 years ago

Great idea!!! SQLite is an extraordinary product. I'll be following Bedrock.

This could be, for databases, what node was for server-side programming. There are parallels, you're using a "client side single-writer (excellent) DB" and making it apt for the cloud with Paxos. Again, great idea!!!!

And it seems you're taking with a good humor some "strong" comments here. +1 sr. +1 to u.

quinthar45• 10 years ago

Thanks, strong comments welcome!

lucio3• 10 years ago

How does the client get "redirected" to another node if the one you're talking to fails? It is transparent to the client?

quinthar45• 10 years ago

Our PHP library has the concept of a primary and failover host. We recommend configuring a local Bedrock node as the "primary host", and then setting up a load-balanced pool of all nodes to be used as the "secondary host". This means in normal operation, every webserver talks directly its nearest node (bypassing the load balancer), but "fails over" to the load balancer if the primary is down.

Granted, a simpler configuration is to just have two load balancers -- both of which have all nodes -- and then use each as the primary/secondary. We did this for years and it was fine, but for just a tiny bit more configuration overhead you can bypass the load balancer for the primary and thus shave off those precious milliseconds from each request.

kbaker2• 10 years ago

OK, how is this different from Rqlite [1], except in C++ instead of Go, Paxos instead of Raft?

rqlite is a distributed relational database, which uses SQLite as its storage engine.
rqlite gives you the functionality of a rock solid, fault-tolerant, replicated relational database, but with very easy installation, deployment, and operation.

Hmmm....

Also, is Bedrock DB only 30 days old? (since the 'first commit' message on GitHub?) That's barely topsoil!

[1] https://github.com/rqlite/rqlite

quinthar45• 10 years ago

Haha, Bedrock has been in continuous development and production use (remember: this powers all of Expensify's and has since day one) for about 8 years. However, the public repo is very new.

I'm not actually familiar with Rqlite, but wow, it does look very similar. Thanks for the tip! Does anybody use it at scale?

kbaker2• 10 years ago

Ah I see. So you are saying after enough weathering you have exposed the Bedrock...

I have no idea if anyone uses Rqlite, I just remember it from previous discussions here. Very similar indeed...

bithavoc• 10 years ago

Also with identical approach there is http://www.actordb.com

quinthar45• 10 years ago

Oh, neat! That one seems to replace SQLite's storage engine with a custom one. But yes, also similar. Cool! Again, what is the largest real-world user? We've found a lot of the theories tend to break down when they are subjected to reality -- Bedrock's advantage is it's been hardened in the crucible of live production traffic for years.

marknadal• 10 years ago

I think it is important to encourage people to build their own databases, so I want to commend you guys for doing it. But I do have some questions (disclosure: I am the author of https://github.com/amark/gun ):

- Is it correct to say that Bedrock is primarily a replication layer for SQLite? Most things your homepage highlight seem to be SQLite features, not Bedrock features.

- Elsewhere in this thread you mention you run PAXOS (what implementation are you using? Your own? Do you have a test we can run to verify correctness?) But then you mention you sacrifice the "C" in the CAP Theorem, which would go against any point of having PAXOS. What happens in a split-brain scenario, where you have lets say 6 peers, and there is a network partition straight down the middle?

- You also mention elsewhere in this thread that if you are talking to the same node (a sticky session) there is no consistency issues. Do you mean linearizable? Because consistency has to do with multi-machine data consistency. For instance, if a write happens on another peer, then the node you are talking to should return that write not a stale write.

- Is there anything other than just assuming it is run on SSD that make it faster than SQLite on SSD?

Thanks!

quinthar45• 10 years ago

Re: SQLite -- Yes, Bedrock is just the replication layer, SQLite does all the SQL and storage.

Re: Paxos -- It's our own implementation. Split brain is prevented by the master refusing to stand up unless a majority of configured (not just active) slaves approve its standup request. So in a 6 node deployment, 1 master and 5 slaves, 3 of the slaves would need to approve. This means one "half" would have 4 nodes, and the other would have 2 -- and the half with 2 would recognize it doesn't have quorum and thus stay idle. In a scenario where there is a split down the middle, nobody would do anything because nobody has quorum. (This is precisely why you shouldn't deploy in just 2 datacenters -- three is the magic number.)

Re: Sticky sessions -- True multi-machine consistency is impossible to guarantee and has no real practical application. The only consistency that matters is from the perspective of an observer, ensuring that it always sees a world whose time arrow progresses linearly forward. If that is what "linearizable" means, then perhaps. Sorry, my terminology could be off. Thanks for the correction!

Re: SQLite on SSD -- Sorry, I didn't mean to claim Bedrock was somehow faster than SQLite. Indeed, Bedrock adds overhead to SQLite (to do all the networking and such). My main claim is that Bedrock is faster than other databases, in particular when using C++ stored procedures for complex operations.

Thanks for the questions!

toolslive• 10 years ago

Is the set of servers that participate a paxos value too (ie determined using the consensus algorithm), or is it configured ? Can you grow a cluster without bringing it down ?

msackman• 10 years ago

Paxos: I've been trying to look for that. Having cloned the code and grepped for paxos I'm getting no hits. Where is the paxos implementation?

lucio3• 10 years ago

Can u show stats of bedrock use in expensify? How many users? How many nodes? How many transactions per second? queries per second? DB size? largest table rowcount? node failures per month? how many times have u had a master failure? network partition incidents?

quinthar45• 10 years ago

I should get better stats. 4.5M users, 6 nodes split between 3 datacenters. Each node has 16 CPUs. 2158341079 total write transactions (over 8 years); not sure how many read (10-100x more?). I'll try to get better stats on peak read/write transactions per second. Not sure the total number of rows of the largest table (that actually takes a long time to count).

Counting "failures" is difficult -- if it breaks, it's because of some bug in our application logic (eg, our stored procedure). Most of our restarts are due to normal maintenance and upgrades. In the history of the company there were a handful of core problems to the logic (generally as we encountered some weird edge case for the first time), but I can't remember the most recent.

Regardless, I'll try to get better data on this. Thanks for asking!

ngrilly10• 10 years ago

6 nodes split between 3 datacenters

This makes 2 nodes per datacenter. Do the 2 nodes cooperate in some way, or are they fully independent from each other (like shards)?

spotman2• 10 years ago

2 billion writes over 8 years? Cool if so, but many database systems both MySQL, and others are capable of getting this in a day. I know this because I maintain some high availability MySQL systems that see about 4 billion writes per day across a similar amount of hardware.

Have you run this through Jespen or done any actual load testing or deep testing for failures related to machines dying, network partitions or other?

I encourage you to do so, because (not trying to sound rude) this kind of reads like "hey my homemade car has 25,000 miles on it and I still use it". But you can build a performance and failure testing framework to really put it through its paces.

Anyhow , have fun and good luck~~

Animats• 10 years ago

So where are the other copies? The documentation tells you how to set up Bedrock locally, but to get redundancy, you need multiple copies talking. How do you set that up?

And how does security work?

quinthar45• 10 years ago

Here's a quick overview of how to configure in multiple zones: http://bedrockdb.com/multizone.html

Security isn't provided by Bedrock (or really, any database, at least not well). Rather, with Bedrock security is the responsibility of the application layer, but built into the database via stored procedures.

nvartolomei• 10 years ago

Bedrock is designed from the ground up to operate in a multi-datacenter environment with rigorous use of stored procedures – the new standard for modern application design.

stored procedures—new standard for modern application design?

quinthar45• 10 years ago

Well, perhaps "new" is relative. But yes, I think strong application design moves the queries into stored procedures that execute inside the database, exposing a higher-level interface to the application layer. This not only maintains better layering from a software engineering perspective, but also provides better isolation from a security perspective:

Your webserver is the first thing to be hacked by an attacker because it's the server that sits on the internet. If all your security logic is built on your webserver, an attacker can easily bypass it all. However, if your security logic is built into your database, then it dramatically limits the damage a hacker can do from the webserver.

In particular, I would recommend you create an "Authenticate" stored procedure that accepts a username and password, returning an "authToken". Then make all your other functions into similar stored procedures, each of which accepts and verifies an "authToken" before returning the results.

(And in the case of Bedrock, you might also disable the Bedrock::DB plugin entirely to prevent direct access to your database from the webserver, forcing everybody to go through your stored procedures.)

This design means attackers who root your webserver can't randomly access your database without knowing the username/password (or valid authToken) -- all of which is neatly and securely contained inside the database itself.

To be clear, if you do keep your SQL on your webserver (as most applications honestly do, though I believe it's a mistake), then the Bedrock::DB plugin is perfect for you. But I think Bedrock::DB (or really, any direct access to a database outside of stored procedures) should be largely viewed as a programming and maintenance convenience, at the expense of security.

harryf• 10 years ago

Hmmm under plugins...

* Jobs - Provides a simple job queue.

* Cache - Provides a simple replicated cache.

...while these look like nice-to-have features which make life easy for developers, IMO having a database which is also a queue and is also a cache is a way to end up with a mess you can't scale out and is hard to reason about.

Have seen this happen with Redis - unless you're disciplined about how you use it and deploy it, having db, cache and queue all in one place is a honeypot for developers that turns into a future nightmare for operations.

quinthar45• 10 years ago

Ya, I'm not sure I agree with that. I understand that argument in theory, but in practice the Jobs and Cache plugins have like 1% as much code as the Bedrock core -- and use all of it. So the idea that it makes sense to have a separate database, job queue, and cache -- despite all doing 99% of the same work -- strikes me as rather redundant and needlessly complex.

In practice, a job queue, a cache, and a database all do largely the same thing: maintain some internal state on disk, respond to some networked API calls, and synchronize across multiple servers. The actual logic of a job queue or cache is pretty trivial compared to what's underneath.

Indeed, I think the lesson of Redis is exactly why you should build these systems on top of a real database: they are struggling to hack on replication and reliable storage, even though these are "free" when built atop a database.

petre• 10 years ago

How is data distributed over multiple hosts? Aside from being replicated, is is sharded? Does it have any sort of redundancy? What happens if you lose a host?

quinthar45• 10 years ago

Every host has all data. (This sounds crazy, until you do the math on how cheap storage is and how comparatively "little" data people actually need in the real world.) So we have 6x redundancy in normal operation, across three datacenters (and three different power grids, three different providers). There are also nightly backups.

naasking• 10 years ago

Linux-only? Or will it run on sqlite-supported platform?

quinthar45• 10 years ago

We do most of the development in MacOS, but deploy it to Linux. I've never compiled it for Windows, but I imagine it would be straightforward.

ngrilly10• 10 years ago

Two questions:

If I'm not mistaken, creating an index is a blocking operation in SQLite (other writers are blocked). How do you manage this in production?

How do you create a stored procedure? Do you have to recompile the whole program? How do you deploy with zero downtime?

quinthar45• 10 years ago

Great questions! Yes, indexing is actually a significant challenge at our scale, as it can take a long time to add and currently, it is a blocking operation. However, the sqlite team is amazing and has all sorts of write-concurrency tricks up their sleeve to allow for creating indexes in a parallel thread. We haven't used it yet, but we plan to.

As for the stored procedures, yes they are written in C++, and thus deploying them requires compiling and upgrading the server itself. However, we have 6 of them (and honestly, any one of which has enough read capacity to satisfy about all our traffic) so a minute of downtime to upgrade for each independently isn't a problem.

The result is zero downtime as perceived by the user, even though each server has occasional downtime for maintenance and upgrades. In general I'd say we upgrade the database about weekly, or more frequent depending on how active we are in the stored procedures.

ngrilly10• 10 years ago

Yes, indexing is actually a significant challenge at our scale, as it can take a long time to add and currently, it is a blocking operation.

What do you do during index creation: Do you drop write requests on the floor? Do you store them in a persistent queue somewhere? Or do you remove a node from the cluster, create the index, re-add the node to the cluster, and repeat this on every other nodes?

I'm asking because at some point I thought of using SQLite, embedded in a process containing the business logic and the network layer, but I abandoned this idea specifically because of blocking operations like index creation, and decided to use PostgreSQL instead.

the sqlite team is amazing and has all sorts of write-concurrency tricks up their sleeve to allow for creating indexes in a parallel thread

I'd be very interested in any link related to this new feature of SQLite.

However, we have 6 of them (and honestly, any one of which has enough read capacity to satisfy about all our traffic) so a minute of downtime to upgrade for each independently isn't a problem.

So, basically, you're doing a rolling upgrade? Have you evaluated compiling your stored procedures to dynamically loaded libraries, or using an interpreted language like Lua/Python/JavaScript?

didip• 10 years ago

To take this further, perhaps pay Aphyr for his time and run Jepsen tests?

alucab• 10 years ago

Hi this is very interesting. Can you elaborate on your concept of plugin development ?

You clearly state that your ideal model is to develop plugins that are embedded in the DB to execute core business functionalities. However, in the website there is only tutorial documentation about the SQL interface.

Is the only guide the code for now ?

Thanks !

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