When to use MongoDB or other document oriented database systems

Question

We offer a platform for video- and audio-clips  photos and vector-grafics  We started with MySQL as the database backend and recently included MongoDB for storing all meta-information of the files  because MongoDB better fits the requirements  For example  photos may have Exif information  videos may have audio-tracks where we to want to store the meta-information of  too  Videos and vector-graphics don t share any common meta-information  etc  so I know  that MongoDB is perfect to store this unstructured data and keep it searchable   However  we continue developing our platform and adding features  Now one of the next steps will be providing a forum for our users  The question that now arises is  use the MySQL database  which would be a good choice for storing forums and forum-posts  etc  or use MongoDB for this  too   So the question is  when to use MongoDB and when to use a RDBMS  What would you take  mongoDB or MySQL  if you had the choice and why would you take it

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Who needs distributed  sharded forums  Maybe Facebook  but unless you re creating a Facebook-competitor  just use Mysql  Postgres or whatever you are most comfortable with  If you want to try MongoDB  ok  but don t expect it to do magic for you  It ll have its quirks and general nastiness  just as everything else  as I m sure you ve already discovered if you really have been working on it already   Sure  MongoDB may be hyped and seem easy on the surface  but you ll run into problems which more mature products have already overcome  Don t be lured so easily  but rather wait until  nosql  matures  or dies   Personally  I think  nosql  will wither and die from fragmentation  as there are no set standards  almost by definition   So I will not personally bet on it for any long-term projects   Only thing that can save  nosql  in my book  is if it can integrate into Ruby or similar languages seamlessly  and make the language  persistent   almost without any overhead in coding and design  That may come to pass  but I ll wait until then  not now  AND it needs to be more mature of course   Btw  why are you creating a forum from scratch  There are tons of open source forums which can be tweaked to fit most requirements  unless you really are creating The Next Generation of Forums  which I doubt

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to store this unstructured data   As you said  MongoDB is best suitable to store unstructured data  And this can organize your data into document format  These RDBMS altenatives called NoSQL data stores  MongoDB  CouchDB  Voldemort  are very useful for applications that scales massively and require faster data access from these big data stores   And the implementation of these databases are simpler than the regular RDBMS  Since these are simple key-valued or document style binary objects directly serialized into disk  These data stores don t enforce the ACID properties  and any schemas  This doesn t provide any transaction abilities  So this can scale big and we can achieve faster access  both read and write     But in contrast  RDBM enforces ACID and schemas on datas  If you wanted to work with structured data you can go ahead with RDBM   I would choose MySQL for creating forums for this kind of stuff  Because this is not going to scale big  And this is a very simple  common  application which has structured relations among the data

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I ve seen at lot of companies are using MongoDB for realtime analytics from application logs  Its schema-freeness really fits for application logs  where record schema tends to change time-to-time  Also  its Capped Collection feature is useful because it automatically purges old data to keep the data fit into the memory   That is one area I really think MongoDB fits for  but MySQL PostgreSQL is more recommended in general  There re a lot of documentations and developer resources on the web  as well as their functionality and robustness

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After two years using MongoDb for a social app  I have witnessed what it really means to live without a SQL RDBMS    You end up writing jobs to do things like joining data from different tables collections  something that an RDBMS would do for you automatically  Your query capabilities with NoSQL are drastically crippled  MongoDb may be the closest thing to SQL but it is still extremely far behind  Trust me  SQL queries are super intuitive  flexible and powerful  MongoDb queries are not  MongoDb queries can retrieve data from only one collection and take advantage of only one index  And MongoDb is probably one of the most flexible NoSQL databases  In many scenarios  this means more round-trips to the server to find related records  And then you start de-normalizing data - which means background jobs  The fact that it is not a relational database means that you won t have  thought by some to be bad performing  foreign key constrains to ensure that your data is consistent  I assure you this is eventually going to create data inconsistencies in your database  Be prepared  Most likely you will start writing processes or checks to keep your database consistent  which will probably not perform better than letting the RDBMS do it for you  Forget about mature frameworks like hibernate    I believe that 98  of all projects probably are way better with a typical SQL RDBMS than with NoSQL

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In NoSQL  If Only It Was That Easy  the author writes about MongoDB      MongoDB is not a key value store  it   s quite a bit more  It   s definitely not a RDBMS either  I haven   t used MongoDB in production  but I have used it a little building a test app and it is a very cool piece of kit  It seems to be very performant and either has  or will have soon  fault tolerance and auto-sharding  aka it will scale   I think Mongo might be the closest thing to a RDBMS replacement that I   ve seen so far  It won   t work for all data sets and access patterns  but it   s built for your typical CRUD stuff  Storing what is essentially a huge hash  and being able to select on any of those keys  is what most people use a relational database for  If your DB is 3NF and you don   t do any joins  you   re just selecting a bunch of tables and putting all the objects together  AKA what most people do in a web app   MongoDB would probably kick ass for you    Then  in the conclusion      The real thing to point out is that if you are being held back from making something super awesome because you can   t choose a database  you are doing it wrong  If you know mysql  just use it  Optimize when you actually need to  Use it like a k v store  use it like a rdbms  but for god sake  build your killer app  None of this will matter to most apps  Facebook still uses MySQL  a lot  Wikipedia uses MySQL  a lot  FriendFeed uses MySQL  a lot  NoSQL is a great tool  but it   s certainly not going to be your competitive edge  it   s not going to make your app hot  and most of all  your users won   t care about any of this       What am I going to build my next app on  Probably Postgres  Will I use NoSQL  Maybe  I might also use Hadoop and Hive  I might keep everything in flat files  Maybe I   ll start hacking on Maglev  I   ll use whatever is best for the job  If I need reporting  I won   t be using any NoSQL  If I need caching  I   ll probably use Tokyo Tyrant  If I need ACIDity  I won   t use NoSQL  If I need a ton of counters  I   ll use Redis  If I need transactions  I   ll use Postgres  If I have a ton of a single type of documents  I   ll probably use Mongo  If I need to write 1 billion objects a day  I   d probably use Voldemort  If I need full text search  I   d probably use Solr  If I need full text search of volatile data  I   d probably use Sphinx    I like this article  I find it very informative  it gives a good overview of the NoSQL landscape and hype  But  and that s the most important part  it really helps to ask yourself the right questions when it comes to choose between RDBMS and NoSQL  Worth the read IMHO   Alternate link to article

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Like said previously  you can choose between a lot of choices  take a look at all those choices  http   kkovacs eu cassandra-vs-mongodb-vs-couchdb-vs-redis  What I suggest is to find your best combination  MySQL   Memcache is really great if you need ACID and you want to join some tables MongoDB   Redis is perfect for document store Neo4J is perfect for graph database  What i do  I start with MySQl   Memcache because I m use to  then I start using others database framework  In a single project  you can combine MySQL and MongoDB for instance

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The 2 main reason why you might want to prefer Mongo are   Flexibility in schema design  JSON type document store   Scalability - Just add up nodes and it can scale horizontally quite well    It is suitable for big data applications  RDBMS is not good for big data

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You know  all this stuff about the joins and the  complex transactions  -- but it was Monty himself who  many years ago  explained away the  need  for COMMIT   ROLLBACK  saying that  all that is done in the logic classes  and not the database  anyway  -- so it s the same thing all over again   What is needed is a dumb yet incredibly tidy and fast data storage retrieval engine  for 99  of what the web apps do

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I would say use an RDBMS if you need complex transactions  Otherwise I would go with MongoDB - more flexible to work with and you know it can scale when you need to   I m biased though - I work on the MongoDB project

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Note that Mongo essentially stores JSON   If your app is dealing with a lot of JS Objects  with nesting  and you want to persist these objects then there is a very strong argument for using Mongo   It makes your DAL and MVC layers ultra thin  because they are not un-packaging all the JS object properties and trying to force-fit them into a structure  schema  that they don t naturally fit into   We have a system that has several complex JS Objects at its heart  and we love Mongo because we can persist everything really  really easily   Our objects are also rather amorphous and unstructured  and Mongo soaks up that complication without blinking   We have a custom reporting layer that deciphers the amorphous data for human consumption  and that wasn t that difficult to develop

[mysql] When to use MongoDB or other document oriented database systems?

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