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Canonical drops CouchDB because they were unable to make it scale up (slashdot.org)
110 points by patrickaljord 1278 days ago | 36 comments



I had the chance to speak to one of the Couchbase guys about Ubuntu One-like systems at Couchconf, and gained some (limited) knowledge. Be aware that some of this is guesswork, as I don't know Ubuntu One all to well.

First things first: I think the failure of "really large systems" does not mean that the underlying technology is bad - most likely, it was a wrong pick for all the specific cases that this product needs. The number of variables is just so high that what looks like a good pick first, is bad in hindsight. As far as I know, Ubuntu One is one of the largest CouchDB based systems. (Zynga being the other)

As far as I learned, it is an Authorization/Authentication issue, more than a performance issue. So, the proposed solution for such systems is to use (at least) one CouchDB database per user - CouchDB supports authentication per Database, so this usage is perfectly fine. So each user gets n Databases that are named after some clever scheme (lets say "{username}/{contacts}", couchdb allows "/" in database names). Actually, as far as I learned, CouchDB handles this without major problems. The data model is also great: you can replicate data between all the users cell phones, desktops etc. just by replicating the correct database. So far, no problems.

The problem is sharing. So lets say, I want to share my business contacts with my co-founder. CouchDB only allows database-level authentication, so once I give my co-founder access, he will see all of my contacts. This includes the Replication API: once I have access, I can basically slurp the whole database (filters cannot be enforced). So, as you can manage a whole universe of databases, the solution here is simple: setup another database, say "{myuser}-{mycofounder}/shared_contacts", give both of us access and setup filtered push-replication in my database to the other database. So, now the source replicator can be trusted to be mine. So, suddenly, my nice "To the Cloud? Out of the door, left line, one database each"-system turns into a really big graph where every relationship between datasets is a database itself, along with many processes caring for moving data along those lines. Also, once my data is shared with my co-founder, its is basically public, as I readily copied it to him - deletion becomes a messy topic. (As long as the replication chain is intact, deletions are propagated, but honestly: who wants to support such a system?)

So, along those lines, one big problem becomes obvious: CouchDB does not support document-level authentication. Considering the data model of CouchDB (basically, views are aggregations of the global document store), this is also a hard thing to do, because it means that every view has to be filtered per user. On the upside: the Couchbase also said that they would really like to support it.

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Cool story, and seems to make a lot of sense.

It brings up one thing I've been wondering about for a while already - I've always found that CouchDB's authentication feels more "bolted on" than anything else, and this is a nice use case where it doesn't fit.

I love Couch, but I'd have loved for the authentication scheme to be an entirely separate layer, more customizable and programmable, less "one per database, period.".

Such a design would probably cause all kinds of other problems again, though, but I wonder to what extent this has been thought through.

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Here's the comment that John Lenton from Canonical made about this on /.

http://linux.slashdot.org/comments.pl?sid=2539244&cid=38...

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I'm curious if they tried to employ BigCouch, the dynamo-esque fork of CouchDB.

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+1 - good idea. BigCouch is very nice, and based on Cloundant's experiences with it (they wrote it), it seems to scale to handle very large data customers.

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In my experience, bigcouch isn't mature enough for prime time, yet. Admin of it can get very tricky.

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I'm curious. Would be willing to elaborate a little more?

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This might sound like a big deal but it shouldn't be a headliner. Whatever the details (and we don't have many) companies use and drop technologies on a fairly regular basis. Sometimes it's a good fit and sometimes it's not. Obviously in this case Couch didn't do everything Canonical needed (I think someone else actually pointed out that Canonical mentioned that their needs were unique).

For every Canonical that drops Couch there will be 10s of other companies that adopt it because it's a good fit there. All this should reinforce is that every tool has a good fit and that smart implementors pick the one that jives best or moves to a better one when the opportunity presents itself.

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Original link: http://www.h-online.com/open/news/item/Canonical-dropping-Co...

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So.... old technologies suck because they're stable and scale, and new technologies suck because they're fun but aren't stable when they scale?

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This article is a good example of how myths are created and engineering ignorance is perpetuated.

CouchDB doesn't "scale"? If you're trying to "scale" with it, you don't know what you're doing in the first place. CouchDB federates. That's a wholly different thing. And in terms of federated databases, I challenge anyone to come up with one as good or better than CouchDB. (And if you do, it will be news to me, and I'll thank you profusely!)

If its not obvious to you how to scale a federated database, then its not couchDB that can't scale, its you. (which is ok, everyone has to learn sometime, just don't put forth your lack of knowledge as proof of a weakness in an open source product!)

Further, rather than just saying "We've got this great new invention-- a better technology, and we're moving to that!" the message seems to be "we are just wanting to re-invent the wheel, so to justify it, we have to make a negative claim about couchDB.

Now, I expect some particular databases[1] fans to tell us, in the future, that "couchDB doesn't scale".

Ironically, they're punting on CouchDB to use, among other possibilities, SQLite. To claim that "Scaling" is the problem is .... bad engineering form.

CouchDB is great if you want to federate, have databases across the planet talking to each other and keeping in sync (its almost a turnkey CDN in a way), want to run a noSQL DB on a mobile device, etc.

MongoDB is great if you care about SQL and single node performance and its complex distribution mechanism works for you.

IF you want "scale" your choices are Riak or CouchDB-- for "scale" where homogenous distributed servers are the best solution.

And of course there's Cassandra and graph databases, etc. which provide different solutions to scalability.

IF you're serious about scalability, I strongly recommend people look at and choose Riak. I don't think anything out there touches it-- at least for the type of data I need. Cassandra and what I consider the "more complicated" alternatives might fit your particular problem type well. And if you think that its silly of me to recommend Riak then this is probably the case for you. But in terms of general databases, Riak seems to be pulling away from the pack. IF you're a fan of CouchDB, then BigCouch is a dynamo/Riak like version of it that I understand to be quite good. Plus, since its based on CouchDB, if the CouchDB way of doing queries (which is distinctly different from Riak) fits your way of working, then BigCouch deserves a look.

But please, don't ever say "couchDB doesn't scale". If you do, really its that you don't scale, CouchDB is fine.

[1] In an earlier edit I named a database. That was a mistake, not only is it bad form, I don't think that my characterization is appropriate at this time, as that database's fans are not as rabid as I imply. Apologies.

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> If you're trying to "scale" with it, you don't know what you're doing in the first place

They said they worked with the company behind CouchDB and were not able to make it scale. So while you might accuse Canonical of not knowing what they're doing, I doubt you could say the same of the founders of CouchDB. Here is the official announcement [1]:

> For the last three years we have worked with the company behind CouchDB to make it scale in the particular ways we need it to scale in our server environment. Our situation is rather unique, and we were unable to resolve some of the issues we came across. We were thus unable to make CouchDB scale up to the millions of users and databases we have in our datacentres, and furthermore we were unable to make it scale down to be a reasonable load on small client machines.

[1] https://lists.ubuntu.com/archives/ubuntu-desktop/2011-Novemb...

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They worked with them for THREE YEARS, but obviously they don't know what they're doing /sarcasm

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No. It's not even an article, it's slashdot. In the post someone links to an article on some website which again links to the canonical mailing list. https://lists.ubuntu.com/archives/ubuntu-desktop/2011-Novemb...

There John Lenton lays out in not so many words that "for the last three years we have worked with the company behind CouchDB to make it scale in the particular ways we need it to scale in ourserver environment. Our situation is rather unique, and we were unable to resolve some of the issues we came across..."

This sounds like a fair assessment to me. No "myths created", no "ignorance perpetuated".

I would also say that for every kind of technology at some point it's fair to say that it does not scale or is not sufficient in other ways.

Or to say it with couchDB: relax!

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I think what nirvana is worried about is that this will get simplified to "CouchDB doesn't scale" for developers who don't know all the circumstances. It's the slashdot blurb that landed in the front page of HN, not the sober list post.

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+1

It's like saying "$hot-software-de-jour doesn't scale" when the article actually said "we couldn't get it to scale in our server environment - which is a cluster of Arduinos powered by solar cells".

There's nothing wrong with having a workload/architecture/environment that doesn't suit a particular piece of software, and if you do it's right to choose something else that does suit your needs. Saying (or implying) that piece of software is bad because it doesn't suit _your_ strange requirements is about as credible as saying "Photoshop sucks 'cause it can't send email!"

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I have read quite some things on the different larger key-value stores, especially on how they scale. And what I have seen I really like Riak as well. However, we have been setting it up over the last few weeks, and sofar it's less stable than I have hoped/expected: we have had nodes crash for no apparent reason. I hope we can resolve them, as I really like the model, especially the horizontal scaling, but it must be stable to use...

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There are worse things than crashing. Like soldiering on and corrupting data.

The most unstable clustered database I have ever come across was suffering from broken TCP drivers. Never assume a cause until you have actually tracked it down.

I agree with itaborai83 that individual node crashes shouldn't be as big deal with the consistency model and redundancy offered by Riak. That is one reason you might go with Riak over something that offers stronger consistency, but is more picky about node crashes and recovery.

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but aren't nodes supposed to crash, albeit in a tolerable way? Even though I conceptually like Riak I haven't tried it yet, because the problems that I deal with aren't worth the trouble of setting up a cluster and managing it.

I think that the cluster is supposed to be stable. The nodes, not so much.

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I've never had Riak crash on me. If you are having trouble ask any of the Riak guys and they will bend over backwards to help you. If you have found a crasher bug, I bet they want it fixed more than you do.

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> Further, rather than just saying "We've got this great new invention-- a better technology, and we're moving to that!" the message seems to be "we are just wanting to re-invent the wheel, so to justify it, we have to make a negative claim about couchDB.

Ubuntu re-invent a lot of wheels (sometimes poorly). Just off the top of my head: upstart, unity, launchpad...

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I get the impression that the problem was less about scaling within one database than about scaling across many; Lenton practically says as much about a half dozen messages down-thread. Deploying literally millions of separate databases would be a total nightmare of resource contention, version skew, and general administrative burden. U1 was probably looking for ways to use some sort of multi-tenancy to serve the same number of users with fewer CouchDB instances, and that's the kind of scalability they apparently found lacking. Your point about scale vs. federation, while perhaps accurate and valuable, doesn't seem to address the actual reason for this change.

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That is exactly how I understood the problem. The term "doesn't scale" is far to fuzzy to describe the problem.

I also see no mechanism in CouchDB to solve this. If such a problem exists, I expect a company to react with architectural improvements. If that doesn't happen, the software does not fit the use case and has to be exchanged. This is really bad for the manufacturer for his reputation as well for the user who loses massive amounts of his investment.

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Another one bites the dust, another one bites the dust, bamp bamp, another one bites the dust.

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Mr. Ellison, you're the MS of databases. Don't rejoice too much.

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Much to my surprse, last time we had an Oracle sales team in they mentioned that Oracle is now in the business of NoSQL databases in additional to all the other database products they sell.

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Isn't that basically Berkeley DB?

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No, they make an actual NoSQL database now: http://www.oracle.com/technetwork/database/nosqldb/overview/...

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From the data sheet: "Oracle NoSQL Database is built upon the proven Oracle Berkeley DB Java Edition high-availability storage engine". So it's BDBEE…

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That is for the data store itself, and doesn't mean that the database is NoSQL or not. MemcacheDB for example is a NoSQL database that uses BerkeleyDB as a datastore. No different than you'd use InnoDB or RethinkDB with MySQL.

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Is it significantly different from Riak? They seem very, very similar based on my superficial knowledge.

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It blows my mind that something called Berkeley DB is owned by Oracle. You'd think it'd be a UC Berkeley project.

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Awww.. you mad... I'm so sick of hearing about all these "new" technologies that are so revolutionary, but can't hold a candle to postgres and memcache.

Despite what the brochures tell you, a "degree" from DeVry and 3 hours in a Ruby book doesn't make an architect, and this is one of several "revolutionary technologies", like Ruby, that won't scale and will wither and die.

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Exactly, how does a programming language scale or not-scale? Ruby might be slower and hungrier (memory) than other languages but it's the applications that might or might not-scale.

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Assuming you have the most efficient code possible, the efficiency and speed of the interpreter can still affect the ability to scale an app.

Another thought is, the interpreter may or may not have scaling / clustering available, be it through a built-in functionality or an external queue or something.

Sometimes we have to code around interpreter/speed issues. I work in the JVM languages sometimes. I have to do things differently directly in Java if a particular JVM language I use isn't cutting it. Same goes for ".NET", which is over 30 some languages.

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Go ahead and write your self-congratulatory blogpost when Ruby "withers and dies". If HN is still around in 40-50 years, I'm sure it'll hit the frontpage.

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