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Don't use MongoDB

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Re: Don't use MongoDB

#141

Post by harryh »

Hi,

I run engineering for foursquare. About a year and a half ago my colleagues and I and made the decision to migrate to MongoDB for our primary data store. Currently we have dozens of MongoDB instances across several different data clusters storing over a TB of data and handling 10s of thousands of requests per second (mostly reads but the write load is reasonably high as well).

Have we run into problems with MongoDB along the way? Yes, of course we have. It is a new technology and problems happen.

Have they been problematic enough to seriously threaten our data? No they have not.

Has Eliot and the rest of his staff @ 10Gen been extremely responsive and helpful whenever we run into problems? Yes, absolutely. Their level of support is amazing.

MongoDB is a complicated beast (as are most datastores). It makes tradeoffs that you need to understand when thinking about using it. It's not necessarily for everyone. But it most certainly can be used by serious companies building serious products. Foursquare is proof of that.

I'm happy to answer any questions about our experience that the HN community might have.

-harryh

Re: Don't use MongoDB

#143

Post by regularfry »

latch wrote: post #120
regularfry wrote: post #108

Earlier quoted context omitted.

I honestly have no dog in this race, but an argument which boils down to "MySQL is just as bad" is not one I'd choose to pursue.

I spent the time to write all that, and all you got from it is "MySQL is just as bad"...I obviously did a bad job. edit: I brought up MySQL because I think we all know that companies, you, me knowingly ship products with bug. In fact, you can look at public bug tracking for a bunch of major software and see bug fixes scheduled for future releases. However, if you are going to accuse a database vendor of knowingly shi…

No, of course that's not all I got from it. I was making a point specifically about the comparison you seemed to be making: that because MySQL did something (shipping with stupid defaults, dataloss bugs, whatever), it doesn't count as a black mark against MongoDB if they do the same.

I didn't comment on the rest because I don't care, not because I don't get it.

Re: Don't use MongoDB

#144

Post by rit »

ehwizard wrote: post #138

From CTO of 10gen First, I tried to find any client of ours with a track record like this and have been unsuccessful. I personally have looked at every single customer case that’s every come in (there are about 1600 of them) and cannot match this story to any of them. I am confused as to the origin here, so answers cannot be complete in some cases. Some comments below, but the most important thing I wanted to say is…

One addendum to Eliot's "both our offices hold open office hours"; we (10gen) also recently opened an office in London.

Although we don't yet have a fixed office hours schedule, we typically hold them every 2 weeks. The exact dates are announced via the local MongoDB Meetup Group°; we always hold the hours at "Look Mum No Hands" on Old Street.

At least one (and often several) of our Engineers make themselves available during this time to answer any questions and assist with MongoDB problems.

° http://www.meetup.com/London-MongoDB-User-Group

Re: Don't use MongoDB

#145

Post by kfool »

CarlHoerberg wrote: post #46
jonpaul wrote: post #30

I've used MongoDB in production since the 1.4 days. It should be noted that my apps are NOT write heavy. But, many of the author's points can be refuted by using version 2.0. Regarding the point of using getLastError(), the author is completely correct. But the problem is not so much that MongoDB isn't good, it's that developers start using it and expect it to behave like a relational DB. Start thinking in an asynchr…

Schema-less is imho a overrated feature. ORMs like DataMapper (Ruby) and NHibernate (.NET) can generate the schema on the fly for RMDBS, so no need for migrations pre-production. But when your application is in production you need migrations even with a "schema-less" db! See, rename a field and "all your data" is lost, unless you migrate the data from the old field to the new one..

(Disclaimer: I work on ChronicDB)

I second that: schema-less is misunderstood.

There's a difference between flexibility of schema definition and flexibility of schema change[1].

Flexibility of schema change, which NoSQL does not solve, is increasingly more important. Not just for large data stores but also for the data development process and release process. To avoid playing the suboptimal schema-change game both the code and the data need to be updated together. Or at least be given the illusion that they have[2].

A probably obvious question most developers must have asked by now is: if we've built great tools to version source changes, how come we haven't built great tools to version data changes?

[1] - http://chronicdb.com/blogs/nosql_is_technologically_inferior...

[2] - http://chronicdb.com/blogs/change_is_not_the_enemy

Re: Don't use MongoDB

#146

Post by skrebbel »

ehwizard wrote: post #138

From CTO of 10gen First, I tried to find any client of ours with a track record like this and have been unsuccessful. I personally have looked at every single customer case that’s every come in (there are about 1600 of them) and cannot match this story to any of them. I am confused as to the origin here, so answers cannot be complete in some cases. Some comments below, but the most important thing I wanted to say is…

> If you want to come talk to the MongoDB team, both our offices hold open office hours[2] where you can come and talk to the actual development teams. We try to be incredibly open, so please come and get to know us.

I envy how all your (potential) customers are from California.

Re: Don't use MongoDB

#147

Post by ryanfitz »

I think MongoDB's biggest problem is people expect mongo to take care of all their scalability issues for them. In reality once you start hitting a certain scale you need to start rearchitecting your system, no datastore can automatically handle this for you, but perhaps mongoDB let you get a little bit bigger before this became a big issue.

Re: Don't use MongoDB

#148

Post by joevandyk »

angelbob wrote: post #114
goldmab wrote: post #78

Earlier quoted context omitted.

Fair enough, but you can also have a schemaless store by using JSON fields in PostgreSQL or MySQL.

Not indexably. But you can do a hideous many-tables-per-real-table thing where each field gets a tall thin table in PostGRES or MySQL, do a lot of joins to get your data, and index the fields in that . It's not as awful as it sounds, performance-wise. It is as awful as it sounds in terms of maintainability, of course.

You can index hstore fields in PostgreSQL.

Re: Don't use MongoDB

#149

Post by WayneDB »

moe wrote: post #129
WayneDB wrote: post #119

Earlier quoted context omitted.

I agree with your responses to 1 and 2. I take issue with the example for 3 though because Redis is nowhere near the complexity or feature set of MongoDB.

I don't think that counts as an argument. When you strip MongoDB down to the parts that actually have a chance of working under load then you end up pretty close to a slow and unreliable version of redis. Namely, Mongo demonstrably slows to a crawl when your working-set exceeds your available RAM. Thus both redis and mongo are to be considered in-memory databases whereas one of them is honest about it and the other n…

You know, I didn't think about how similar Redis and Mongo are at the core when I first read your comment. The first thing that jumped out at me was the large set of disparities.

Thanks for that explanation. I agree that Mongo seems to have over-promised and under-delivered and that you do have to really craft your access pattern. I'm not a heavy MongoDB user, but from reading the docs and playing around, I was already under the impression that the performance of MongoDB is entirely up to me and that I would need a lot of understanding to get the beast working well at scale.

So, it's a tough call for me to say whether they over-promised or not, but like I said...I'm not a heavy user. I just read a lot. I do think it is easy to be deceived by Mongo's apparent simplicity (ie - usage of JSON, Javascript, schema-lessness, etc).

EDIT: zzzeek made a good point below about spending time in a low-key mode before really selling the huge feature-set, which convinced me, so I think you're right. I do like the idea of Mongo though, so hopefully they can get through it.

Re: Don't use MongoDB

#150

Post by WayneDB »

zzzeek wrote: post #132
WayneDB wrote: post #119

Earlier quoted context omitted.

I agree with your responses to 1 and 2. I take issue with the example for 3 though because Redis is nowhere near the complexity or feature set of MongoDB.

there's something to be said for promoting an application proportionally to the maturity of its implementation. An application with a larger and more sprawling featureset would need to spend several years in "low key" mode, proving itself in production usage by a relatively low number of shops who treat it with caution. I think the issue here is one of premature overselling.

Good point.
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