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Scaling MongoDB at Mailbox
- stonewhite 13y agoI dont understand how MongoDB can stay as a shiny tool given its long list of shortcomings. It is so elastic that I think it really has no true form (object cache, mq, relational??, key-value bucket). Lately I haven't read any news about a company migrating to Mongo, but rather most were either departing from mongo because of some catastrophic outage or some mission impossible operation to handle the shortcomings, like this one. In its current state it looks more like a prototyping tool that allows you to delay some tech decisions until your product matures, rather than a production tool. Or it is just me that wants at least 5 major versions on his production database.
- mjallday 13y agoSame reason MySQL sticks around when there are alternatives that make it harder to shoot yourself in the foot: Easy to get started, works well enough to make an MVP.
- rdtsc 13y agoMarketing. They marketed the hell out of it. Most developers I know have MongoDB mug. > Lately I haven't read any news about a company migrating to Mongo, but rather most were either departing from mongo They had some strange defaults to start with (to give them serious advantage in small silly benchmarks) like un-acknowledged writes. Yes you read that correctly, for years their default configuration was to throw write requests over the fence and assume they succeeded. There are some horror stories of people's databases becoming silently corrupted. Those corrupted databases were then backed up and back ups were corrupted. Eventually they had fixed their defaults but their reputation as an engineering company went down the hill ( I speak for myself here mostly). From my experience a lot of people using MongoDB don't know what they are using. To them 'unacknowledged writes' and 'database level locks' sounds like Latin. They see short examples, cool mugs, other cool kids talking about how easy MongoDB is and they start using it.
- misiti3780 13y agoor - mongo is great for some problems and not so great for other problems. if there is one thing you can figure out hanging out on HN long enough - it's cool to hate on mongodb
- rdtsc 13y ago> it's cool to hate on mongodb Tens of thousands of computer geeks all randomly chose to hate a product. Clearly a coincidence or unlucky alignment of stars, nothing to do with said product, of course.
- briancaw2 13y agoIt could just be the case that everyone complains about their database and the HN crowd uses a lot of MongoDB. There's certainly more total MySql/MSSQL griping, whether or not gripers/users is higher for MongoDB isn't really obvious.
- rdtsc 13y agoAs I pointed out MongoDB inc (ex 10gen) made some decision in relation to how they marketed and set up their product that made many turn their heads.
- idProQuo 13y agoI want to like Mongo, I'm all about "cutting my teeth on the bleeding edge", but I don't know what to think about MongoDB. Most conversations about it seem to go like this: Lover: MongoDB is so much faster and easier than old school SQL! Hater: It's fast and easy because it doesn't check if it's written data correctly, which leads to corrupt data. Lover: Well you could always turn on the write lock. Hater: If you turn on the write lock, it becomes slower than normal SQL databases. Lover: Well you're just trying to use it the same way you use SQL. MongoDB is great for some problems and not so great for other problems. Hater: What problems is MongoDB better at solving? And then that's the end. I've never heard a convincing use case for this thing. If you can change that for me and give me one, I'd be delighted to listen.
- threeseed 13y agoSimple. There are some use cases for which MongoDB will be 5x faster than any other system. It is relatively unique among databases in that it is a document store as opposed to a relational system. It is also very easy to use and manage.
- Pxtl 13y ago> It is also very easy to use and manage. This is something that SQL database fans don't get. A small start-up can't afford to have a team of guys fiddling with incredibly obscure performance tuning settings. A developer might not know how to optimize a slow-running Postgre query, but he knows how to cache data and denormalize in a manner that makes the query he wants to run fast. And a document-store plays nice with this. Any simple relational beauty of SQL databases falls down once you get over a few million rows, and then the hideous hacks and bizarre settings start coming out. At that point you need a pile of domain-specific knowledge to make them play nice. Mongo takes the domain-specific knowledge out of the equation and lets the developers apply their existing skill-set to the data. I've you've got a thousand employees? Get a few DBAs and Postgre. If you've got, like, five?
- konstantintin 13y agoare there no problems with mongo 'once you get over a few million rows'?
- alrs 13y agoA small startup that invests in some ops talent is going to run rings around a small startup that optimizes for developers. People think that staffing up devs creates agility and speed, when in reality it just increases product features. Scope creep without someone around to voice the needs of operations is a crazy-efficient generator of technical debt.
- stonewhite 13y agoOne thing you don't know or faced yet is that mongo fails, and sometimes it fails so hard that you would rather kick some rocks. For example, if you start a background index generation on an eventually consistent replica set, indexing on secondary nodes are done foreground. Which means you only accept reads from slaves but slaves are unresponsive because of the index generation. In this state, if you try to do anything fancy your data will go corrupt. Only way out is to wait through the outage (which I find it pretty hard to do so). This is still not solved in 2.4, waiting for 2.6. Replica sets with all secondaries which can't elect a primary because it lost a node, or the mostly random primary-secondary switches that drops all connections, seldomly primary reelecting itself meanwhile dropping connections for no apparent reasons. Mongo offers tin foil hats for integrity, consistency and reliability. So yeah, I'd rather examine and understand why an SQL query is slow. Because it is at least deterministic, which in mongo nothing really is. Postgres supports free form json, XML or hstore document formats by the way, couchDb has its own specific features as a document db too. I still don't see why people want to go on with mongo this bad.
- taude 13y agoI think the premise of prototyping tool is pretty accurate. It makes easy to get something up and running and defer any operational knowledge until later. That being said, I don't see why people can't iterate their apps quickly on time-proven relational datastores. While having JavaScript through the stack is nice, I found writing Mongo Queries a PITA with all the curly-braces, etc...
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- ddorian43 13y agoWhy has the new system less write lock? Is it sharded?
- misiti3780 13y agoIt sounds like the new system is a cluster with a single collection. So all writes to the other collections no longer occur, therefore the write locks decreased
- ddorian43 13y agothanks, to everyone use hnotify!
- MichaelGG 13y ago>one performance issue that impacted us was MongoDB’s database-level write lock. People give MSSQL shit for having row-level locks (if you don't use their MVCC option), yet how is it that Mongo runs with a database-wide option and people don't immediately laugh and walk away? Is the hype so powerful that people just shrug about a huge mutex?
- lucisferre 13y agoThe problems people encounter with SQL performance generally (or at least also) are on the read side where query optimization can become a pretty hard problem. Basically, the short answer is people are using SQL and noSQL very differently (as one would expect). cue: someone telling me SQL query optimization is easy and people are just idiots.
- justinsb 13y agoIt's a valid point taken by itself. But I would respectfully suggest that it's not a particularly useful statement, because you're not comparing SQL to anything. "Complex SQL queries are hard" because "complex queries are hard". If there was a magical tool where you could do complex querying and always have the right answer in the minimal time, then these discussions would never arise. (To a debatable extent, that is one of the things people are paying for when they choose a "better" database: the hope that they get closer to the ideal on complex queries) Personally, I would much rather perform a complex query in SQL than NoSQL. The base-line is likely to be not-terrible, which may be good enough for single-use queries. Optimization is much easier (IMHO) - SQL is a DSL for querying and indexing. Compared to having to write code to do that (which seems to be the primary NoSQL approach), the DSL approach seems much more efficient. SQL isn't perfect, but it beats no-DSL-support or another DSL that is even worse than SQL :-)
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- annnnd 13y agoThe caveat being that in document-oriented store (like MongoDB) the queries tend to be simple(r) - after all, you have no joins, so how complex can they be? Instead of complex queries you need to use appropriate document schemes and/or application logic. MongoDB has its problems (for instance document schemes can't be enforced, disk space consumption concept is unintuitive,...) and relational DBs have their strengths (ACID, SQL is standard among DBs,...). But very few people ever reach a point where the global write lock becomes a problem. 10gen knows exactly which features are vital to most of their users and which are not...
- joeblau 13y agoI worked on a project where we used Mongo to collect analytics and while it worked, there were always problems. We had a problem with our shard key so one shard received more data which crashed it, overloaded the other two shards and crashed the whole system. A second issue we had was trying to read from Mongo while we were storing data which caused a lot of lock contention. The question I have is, knowing what you know now, would you have still gone with Mongo?
- aaronblohowiak 13y agoSummary: vertical partition on collection. They wrote some new code to make moving a collection easier.
- raj_bains 13y agoYou need consistency (distributed mvcc), row-level locking and scale-out architecture. Clustrix might be a better fit for the workload. Clustrix customer Twoo.com has 336 core deployment (168 master, 168 slave, 21 nodes each), they have millions of users and billions of transactions per day. Their application still thinks it's talking to a single MySQL database and they don't have a DBA and they have never thought about shard keys etc. We in the database industry should be solving these problems for you.
- wheaties 13y agoWish someone would do that for Postgres.
- lucian1900 13y agoThere's Postgres-XC [1], but it's a fork and I don't know how actively developed. 1. http://sourceforge.net/apps/mediawiki/postgres-xc/index.php?title=Main_Page http://sourceforge.net/apps/mediawiki/postgres-xc/index.php?...
- garbados 13y agotl;dr your system is more complicated than you realize, so scaling it will be more complicated than you think. Also, MongoDB's write lock is a pain in the ass.
- mbroberg 13y agoWe hear similar stories from the field here at Cloudant. Distributed databases, scaling clusters -- that's hard stuff. Nice to see such a thoughtful post.
- mlmilleratmit 13y agoNice work -- that's a hard problem. I've felt some of this pain as I helped Cloudant customers make hot migrations from mongo to into Cloudant. Your first two figures make it clear just how challenging hot-replications are (especially master-master), not to mention handling failure scenarios. For all of the great things about Mongo, there's something very awesome to be said for CouchDB's MVCC replication model. Glad to see that you're open sourcing those tools. Maybe they could be extended to make a MongoDB <==> CouchDB replicator.
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- stonewhite 13y agoI dont understand how MongoDB can stay as a shiny tool given its long list of shortcomings. It is so elastic that I think it really has no true form (object cache, mq, relational??, key-value bucket). Lately I haven't read any news about a company migrating to Mongo, but rather most were either departing from mongo because of some catastrophic outage or some mission impossible operation to handle the shortcomings, like this one. In its current state it looks more like a prototyping tool that allows you to delay some tech decisions until your product matures, rather than a production tool. Or it is just me that wants at least 5 major versions on his production database.
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- bernatfp 13y agoI'm aware of MongoDB issues with scaling, and I'm trying to avoid it as much as I can, but I still can't find any other alternative that offers geolocated queries.
- bonzoesc 13y agoFrom firsthand experience, the PostGIS extension for PostgreSQL is fantastic. A couple of my coworkers at Basho have done geospatial work with Riak, our scalable, distributed database: http://basho.com/indexing-the-zombie-apocalypse-with-riak/ http://basho.com/indexing-the-zombie-apocalypse-with-riak/
- 616c 13y agoSomeone below mentions PostGIS, which from my understanding is among the best tools in the field (if you heard of OpenStreetMap, the whole DB for all their geo data runs on that, and people use dumps like others do with Wikipedia to build their own customized GIS apps on tops of it). That said, other people mention Cloudant deployments here, and that is CouchDB. If you want a Mongo-ish (they are still very different) NoSQL document store (notice I did not say database), there is extra layer of functionality on top of CouchDB known as GeoCouch. I have never personally used it but I have been looking for a reason to. https://github.com/couchbase/geocouch/ https://github.com/couchbase/geocouch/
- jessaustin 13y agoInteresting: ...a single Python process using gevent and pymongo can copy a large MongoDB collection in half the time that mongodump (written in C++) takes, even when the MongoDB client and server are on the same machine.
- MBCook 13y agoI would guess this is for the reason posted in the article: the Python code is multithreaded (sort of, gevent) but the C++ code is only single threaded.
- jessaustin 13y agoSure, but that seems to suggest a meta-reason: the standard utility included with the package isn't asynchronous [sort of orthogonal to threadedness] because it would be a PITA to write an asynchronous utility in C++.
- leif 13y agoThat's not true, I've had no trouble writing very fast threaded C++ programs with the mongo client.
- jessaustin 13y ago1. That's not what I said. 2. I'm sure the Mongo devs would accept pull requests for mongodump.
- leif 13y ago1. > it would be a PITA to write an asynchronous utility in C++ 2. Doubt it, and there's no reason for me to write one for them.
- jessaustin 13y agoAsynchronous ≠ multithreaded. TFA actually tried both ways, measured the difference, and found async to be much faster.
- jyz 13y agoI thought global lock is gone in v2.2 https://blog.serverdensity.com/goodbye-global-lock-mongodb-2-0-vs-2-2/ https://blog.serverdensity.com/goodbye-global-lock-mongodb-2...
- esmet 13y agoIt's at the database level now.
- mcot2 13y agoIt's funny to read these comments trashing mongodb. Perhaps people should do a little less HN ranting and a little more serious study about the problem they need to solve. The design, benefits and tradeoffs of mongodb are well understood. If they don't fit your application, don't use it.
- peedy 13y agotwo writes don't make it wrong?