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Comment by zxcvbn4038 | Hacker News Reader

A lot of companies got lured into using mongodb because it was so developer friendly. It cost nothing and it was easy bring in the back door and alleviated the need for thought.

Then their sales people started coming around and asking for insane sums of money (like $10,000 per instance per year plus 100% markup on hardware to run in AWS - support is extra). They were worried about amazon and others offering a better so next they changed the license.

If it had been SQL it would have been easy to drop in another database. But Mongodb is so different from anything else that you need a major rewrite to get away from it. Postgres has some similiar functionality but it’s not drop in. Amazon has a more or less public beta of DocumentDB which as far as I can tell is a mongodb compatible interface to aurora backend - it works but doesn’t have the polish of RDS yet.

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  > If it had been SQL it would have been easy to drop in another database.

Not true at all. Way too many organisations are locked into Oracle just because it's too hard to switch to something cheaper.

Why is this? If Oracle uses SQL why can you not just export the database, make some transformations, and import it into a PostgreSQL db for example?

Because Oracle uses Oracle's flavour of SQL, and no two databases are feature compatible.

If you are correct then your consultancy can stand to make hundreds of millions and save companies billions on their Oracle instances!

More likely, though, is that Oracle users use Oracle-specific flavors of SQL in lots of legacy apps that no one wants to touch, and rely on the support contracts for continued assistance in keeping the database performant for its query load.

I feel like you’re imagining that SQL is more of a standard interface than it actually is. No two relational databases are quite the same and you’ll be stuck combing through your entire app looking for obscure syntax usage that depends on Oracle specific extensions or quirks.

There’s no incentive to not extend or try to improve SQL semantics because for proprietary databases it increases lock-in which is good for sales and for OSS databases the extensions are genuinely positive and increase developer productivity and you don’t feel bad about locking your users in because it’s OSS.

I think it is probably easier to port from one SQL dialect to another, than from Mongo’s hokey JSON based query language to anything else.

Also not easy.

We tried to do a migration from Sql Server to Postgres.

Even went as far as building a parser/compiler to transform Sql. Certain things are just too difficult to handle.

1. Sql Server supports arbitrary sql statements in queries. Postgres does not.

2. Data types are not the same.

3. Feature sets at the 'interface edge' between the client library and the engine differ. For example, Sql Server queries can return an arbitrary number of results.

It's true that Mongo uses a custom language, but with Mongo - you are unlikely to have any significant business logic in your data layer.

Also their API surface is relatively simple.

For example, FoundationDB has a layer that mimics the Mongo API. Amazon has one as well.

Including Amazon, until recently.

Well there is pl/sql for instance that oracle has, migration costs would be too high for most people. We use pl/sql extensively at work, I cannot even imagine the effort(time/money/people) it would take to migrate from oracle.

Relational/SQL databases still follow the same fundamental data model and query language, despite the differences in SQL syntax. I will argue migration is still easier. Just avoid stored procedures which complex logic, since these are essentially proprietary programming languages.

Even without stored procedures, its not easy.

To really take advantage of a database engine, you will probably end up using engine-specific idioms.

Postgres and Sql Server support recursive CTEs. MySql probably doesn't?

Sql Server supports cursors but is dog slow and generally not recommended for any sort of large scale operations.

Isolation levels and locking are really important as well. Do all engines even support the same isolation levels?

Maybe I'm misunderstanding, but I thought the new license is just about offering MongoDB as a service by itself. But if you're making any other sort of website and use MongoDB as a database, you can still install it and use it for free.

If the companies got lured into using MongoDB as a service, then I understand that prices could increase and companies could be in a pickle. But if companies got lured into using MongoDB as software, I don't see how they could have a problem.

You're correct, the new license only prevents AWS and other cloud from running the MongoDB software itself as a managed service unless they open-source their entire platform (although, as we see with DocumentDB, they can legally implement the API without the license coming into effect).

The parent comment states "their sales people started coming around and asking for insane sums of money" but I can't find any reference to this.

This was my understanding of the license as well. I read through the block and it very clearly suggested only selling the database as a service was not okay. Using the database as a data store should be fine.

If MongoDB really is sending salespeople to make claims against companies who they convinced to use their OSS database as a data-store, than they are indeed abusing their license and no one should use their database or support their company.

From what I read of the license, that shouldn't be the case though.

The fact that mongo was willing to screw over one set of users makes me worry they'd be willing to screw over all their users. It's a risk I wouldn't take, especially when there are so many other (arguably better) options out there.

I wouldn't choose mongo for many reasons, but this licensing change isn't one of them. It's in line with the general spirit of the GPL: if you're going to stand on the shoulders of giants, you should allow others to stand on your shoulders.

The only major change to the license is in adapting to the rise of cloud services.

The GPL is only a copyright license. The GPL DOES NOT impose restrictions on usage, where "usage" vs "distribution" gets defined by copyright law itself.

That's one of GPL's biggest strengths.

Also successful software packages that are GPL are GPL for everyone. You don't have a mother company that can bypass the GPL due to them owning the copyright. And when you do it's usually a scam that people can smell.

You can't say about a license change that it is in the "spirit of GPL" when the mother company, MongoDB Inc, doesn't have to play by the same rules as everyone else.

So I'm sorry, but when you're talking about the "spirit of GPL", you don't know what you're talking about.

https://www.mongodb.com/licensing/server-side-public-license...

The FAQ for the license change very clearly indicates that your reading is what was intended. Question #4 particularly contains the complete text of the section that was altered, and it's hard to see how they could have left themselves any room to penalize regular users.

But Mongodb is so different from anything else that you need a major rewrite to get away from it.

Well actually....

One corner case. If you are using Mongo with the Mongo Linq driver in C#, you can switch it out for an RDMS without changing too much code with just a little foresight.

So why not just use a RDMS from day one?

Because we had data that fit better in a non relational store. We stored data that created from user generated forms and we loaded data back into those forms.

Why use a relational store? If you’re working with a system that will only be read and written by an object based language? Why keep converting back and forth between a relational model and an object oriented model?

In C#

  var seniorMales = from c in context.Customers 
  where c.Age > 65 && c.Sex == “M”

Would be translated at runtime to either MongoQuery, Sql, a foreach loop, etc depending on what “context” represented.

You get autocomplete and compile time checks.

When you want to add an record to your Mongo collection, you work with strongly typed

  IMongoCollection<Customer>

And the compiler will ensure that your collection stays consistent.

That doesn't make sense - how are you eventually moving to a RDBMS if your data is not suited to it?

What do you mean how?

Anything that you can store in object database you can normalize and store in an RDMS. ORMs have been translating relational models back and forth to object models for decades.

In the case of Mongo, you just create one object containing other objects, lists, arrays etc and the driver serializes it to a JSON like structure and stores it as is in the collection.

In the case of an RDMS, you create your C# classes to model your tables and relationships.

The driver translates the LINQ to the appropriate query language.

> Why use a relational store? If you’re working with a system that will only be read and written by an object based language? Why keep converting back and forth between a relational model and an object oriented model?

Well I can't tell you what the right choice in your system is, but in the general case I think going with a relational model by default generally makes sense because it's rather future proof. By that I mean a relational model gives you the most flexibility in the future to evolve your system in ways you couldn't/didn't anticipate when the system was initially designed.

If your data store is behind an API you modify the API. You’re often using a different database for your OLAP and OLTP anyway.

I think you got it backwards. A relational schema change is required and probably a data reindex or reload when you change a data model so relational is the least flexible as opposed to something like Mongo nosql?

If you’re just talking about storing and retrieving documents in a hierarchy with a semi-fixed format then aren’t you asking for a filesystem?

How do you propose that you query a filesystem? In this context, we are referring to a “document” as a structured JSON document. You still have a semi known structure with fields that you can index and query.

A schema change can handle changes needed to existing data, if you don't do that then sure Mongo is easier, but then you've broken data in your system.

I worked on a project with similar requirements. I just serialized the data with protobufs, encrypted it, and stashed it in S3. It was sensitive data so this also had the advantage of being easy to secure and audit.

No point using a relational db for that kind of thing.

And then when you need to do reports on the data and query it?

Why not just use Postgres, set a field as jsonb, done?

Why use Postgres just to store JSON? The entire tooling around Mongo is better for JSON Data.

Not to mention the LINQ driver....

And you can’t do updates on individual JSON fields in Postgres.

Yes you can - this is an article crated in 2017 https://www.idalko.com/crud-operations-postgres-jsonb/

From the article,

The problematic part with PostgresSQL JSONB is modifying a JSONB column content. In any case, we totally replace the old content by a new one. So, the update operations turn to the complex queries that can lose the content. You can avoid this by performing the full JSON reorganization before the persistent operation.

You still don’t have the richness of MongoQuery and the aggregation framework and the tooling around working with JSON data isn’t there. Let alone the native driver support.

Postgres is better than Mongo for all of Mongo’s use cases, and 100 others besides, why wouldn’t you use it?

Including the Mongo aggregation framework, tooling, driver support, in the case I mentioned LINQ support, various reporting packages, etc?

Due to the sensitive nature of the data and the need to keep it encrypted, breaking it down by columns into a schema we could query was a non goal.

A lot of people have difficulty trying to organize complex hierarchical data into rows and columns. A lot of places make you go through a dba to create or change a database which rubs power users the wrong way - and admittedly most of the dbas I’ve worked with are a lot more concerned with making backups fast then in your applications performance. Mongodb doesn’t make you do any of that. It doesn’t make you have authentication either. I think that’s a big reason why it got so popular.

Database versioning and migrations are a pain. I’ve tried both home grown and commercial database systems to make database changes part of the CI/CD process. I haven’t found one that I liked.

When I did implement a system with C#/Mongo, I fell in love with changing my database schema just by changing my C# objects. With the C# driver you can include a Dictionary as part of your object to round trip unmapped fields.

Not to mention that after you go through all of your modeling and figuring out your aggregate roots, you can just store the entire object graph with one .Add and the entire object is stored atomically without having to worry about transactions, table locks, etc.

Unlike with an RDMS where your beautiful aggregate root has to constantly be composed and decomposed.

I think it’s funny that web devs pretty much abandoned hierarchical databases since they are the OG database style.

I think it’s just going to take somebody shaking the cobwebs off of their X.500 manuals and making the query syntax and schemas a little more ergonomic for them to come back en vogue.

It’s one thing to have the ability to mold your DB to model hierarchical data but have your DB engine support it non-awkwardly might be a game changer. People are already used to apps needing a DB, cache, queues, S3, filesystem, service discovery, that adding one more thing would hardly break the bank.

Also Foundation DB supports mongodb clients. It also powers iMessage.

>If it had been SQL it would have been easy to drop in another database.

Hahaha. No.

If anything, migrating from something like Mongo might possibly be easier. Because it's non-relational, you probably have very little business logic in your database layer.

Unlike with Sql.

And even though Sql has a standard syntax, beyond vanilla CRUD queries, there are many differences. Even if 2 engines support the same synatx, the idiomatic way of doing something will differ.

(For example, cursors in Sql Server is extremely slow, whereas its a perfectly acceptable way of doing list operations in Postgres)

> Mongodb is so different from anything else

CouchDB is quietly weeping in a corner.

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