Java Full-Stack Index Q3/2022: Databases
The content of this page is identical throughout Q3/2022 - July, August, and September.
Summary for Q3/2022
- Popularity trend: MySQL is #1 and Postgres #2, beating MongoDB in three out of four categories (it’s neck-to-neck in Google searches and questions at Stack Overflow). All databases lost to Postgres in job ad mentions last month.
- On your current project, keep your existing database unless that database is absolutely, irrevocably, really not working out for you.
- If you need to switch databases or are on a new project:
- If you know that you’ll need the NoSQL features and/or scalability, and you can’t get this with MySQL, then use MongoDB.
- Otherwise, use MySQL.
Archive
| 2022 | Aug | Jul | Jun | May | Apr | Mar | Feb | Jan |
| 2021 | Dec | Nov |
Table Of Contents
Choices
Here are the choices in alphabetical order:
- Apache Cassandra
- Couchbase
- MongoDB
- Oracle’s MySQL
- Neo4j
- Postgres (“PostgreSQL” is the correct but longer name)
I’m only listing open-source products here. I don’t include commercial databases (like Oracle or Microsoft SQL Server) or cloud-proprietary databases (like Amazon DynamoDB or Google Cloud Spanner). Why?
For commercial and cloud products, many other factors play a role in deciding for or against a product - money, legal considerations, existing contracts, vendor relations, etc. Restricting myself to open-source products means limiting myself to technical concerns only - or so I hope at least.
I also have no production experience with NoSQL databases. So I looked at the databases that Spring Data supports and picked what I think are the general applicable NoSQL databases. Please tell me if I picked the wrong ones here!
Popularity
Why Popularity - and How?
Picking a popular technology makes our developer life easier: Easier to learn, easier to build, debug & deploy, easier to find jobs/hire, and easier to convince teammates & bosses. Now popularity can make a difference in two situations: When multiple technologies score similarly, we could go for the most popular one. And when a technology is very unpopular, we may not use it.
I measure popularity among employers and developers as the trend between competing technologies. I count mentions in job ads at Indeed for employer popularity. For developer popularity, I use Google searches, Udemy course buyers, and Stack Overflow questions.
Employers: Job Ads
The Indeed job search is active in 62 countries representing 89% of the worldwide GDP in 2020. It demonstrates the willingness of organizations to pay for a technology - the strongest indicator of popularity in my mind. Postgres is the baseline.
MySQL wins, Postgres is second, MongoDB third. Postgres is still 6% down since March. But MySQL lost heavily and is back down to last November’s numbers. MongoDB is on a three-month slide against Postgres. Cassandra lost a third of mentions against Postgres, Couchbase lost two thirds. Neo4j is the only NoSQL database that held steady and even passed its last place to Couchbase.
Please see here for details, caveats, and adjustments of the job ad mentions.
You can find the detailed search results with links here. They include breakdowns by continents:
Developers
Courses Bought at Udemy
Udemy is one of the biggest online learning sites. They publish the number of courses and students (beyond a certain threshold). This shows how many people evaluate a technology. MongoDB is the baseline. Cassandra, Couchbase, and Neo4j haven’t crossed Udemy’s reporting threshold (possibly around 100,000 students).
MySQL wins, but now MongoDB places second while Postgres is third. MongoDB slowly gains on MySQL and - even slower - increases the distance to Postgres.
Here are the links that show the courses for all and the number of students for some:
Google Searches
Google Trends demonstrates the initial interest in a technology over time.
This link produces the chart. Google Trends only allows five choices, so here’s the link with Couchbase instead of Neo4j - it doesn’t make a difference to the overall picture.
Like Java, MySQL still leads the pack at 1/7 of its peak popularity from 2004. Unlike Java, MySQL’s competitors caught up more: Postgres has 35% of MySQL’s search volume, while MongoDB has 27%. Please note that I changed the Google search for this chart, so it looks different from last month.
So let’s zoom in into the last two years:
This link produces the chart above.
MySQL still wins, Postgres is second, and MongoDB third. MySQL lost about 20% over the last two years, while Postgres and MongoDB stayed flat. Please note that I also changed the Google search for this chart, so it’s different from last month.
Here’s the link with Couchbase instead of Neo4j - it also hovers barely above zero, just like Neo4j.
Questions at Stack Overflow
Stack Overflow Trends shows which percentage of questions at Stack Overflow has a particular technology tag. It is a proxy for using a technology during evaluation and productive use. “More questions = better” to me.
This link produces the chart above.
MySQL wins, Postgres is second, and MongoDB places third. MySQL lost 57% of its question volume since peaking in early 2014 but may be on the rise again. MongoDB and Postgres have been neck-to-neck for the last five years but flat overall for the previous twelve months. Neo4j and Cassandra decrease in lockstep. Couchbase barely hovers above zero.
Analysis
SQL or NoSQL?
When picking a database, we first have to decide whether we want to use a relational database (SQL) or one that foregoes said relations (NoSQL). Relational databases have been around for 40 years. They are trusted workhorses, and we know their strengths and weaknesses. NoSQL is the new kid on the block. So what does it offer that relational databases don’t?
I’ve never used NoSQL in production. So here’s my outside view of the NoSQL advantages. Please correct me if I’m wrong!
Schemaless
We don’t define tables ahead of time. We just start saving our objects. If we add new properties to our classes, we just save them, which changes our database.
No joins
Database normalization is a best practice in relational databases: We keep our tables separate, link them with foreign key relationships, and query them with joins. An example is an order table in an online shop with a customer_id column that links it to our customer table. So far, so good. But when our tables have many records, table joins can be slow or sometimes even impossible to run. It’s my understanding that with NoSQL, there are no joins, and you embed duplicate data from the joined table into your original table. In other words: Denormalization.
Better scaling
When your relational database gets too big for a single server, or that server isn’t fast enough, or you want redundancy, then things get hairy in the relational world: You use sharding to split your data across servers, or you set up database clusters for fail-over and redundancy. None of this is part of the relational model, so it differs from database to database. And running a database cluster with multiple main nodes that our applications can write to is tricky to set up. Not so with NoSQL databases: They were designed to scale, or so they say, and all of this is a lot easier.
Again, without any production experience in NoSQL, I’ve got issues with two of these advantages.
Schemaless
When adding new columns to tables, the ALTER TABLE statement is the least of our problems in my experience. The more significant issue is: How do I fill these new columns meaningfully for my existing data? Let’s say we add a date_of_birth column to a customer table. The default value is probably null. So how do I get the date of birth for all my existing customers? I don’t see how this is getting easier with NoSQL: I still only have one default for my new dateOfBirth property, and I similarly need to somehow get the date of birth for the existing customers.
Still, if we want schemaless in our relational databases, we can also get (most of) that: MySQL has a JSON datatype, as does Postgres.
No joins
Joins don’t work well - or not at all - if we have a lot of records. This means that if we don’t have many records, then joins work just fine. And it seems to me that we can denormalize data just as well in our relational database: We can duplicate the customer columns in the order table if we want to.
The data duplication in NoSQL databases and in denormalized relational ones has side effects, too: If we have properties/columns with customer data in a couple of classes/tables, then we need to update all of them in addition to our main customer class/table when customer data changes.
I’ve also heard that with NoSQL databases, we need to know how we’ll use the data and how we’ll query it before we start storing data. I suppose that’s because of the “no joins” duplication of data. But that doesn’t make much sense to me: Can’t we simply duplicate customer data into our order class after we created the order class? Isn’t the schemaless nature of NoSQL making that especially easy?
To me, the one clear advantage of NoSQL databases over relational databases is better scalability. So if we have a ton of data, then NoSQL databases work better because they were designed for that use case.
Now not all is lost for the relational database fans among us. If you want to host your own database server, then a product like CockroachDB is right for you: A NoSQL database that acts as a relational database on the outside. In the case of CockroachDB, it behaves like Postgres, minus features like stored procedures, triggers, and such. If you need your database in the cloud, then vendors like Amazon, Google, and Microsoft are happy to scale relational databases for you.
Assessment
So here’s my assessment of the candidates:
- There was a time when MySQL was synonymous with “database on the internet”. I mean, MySQL was the “M” in “LAMP stack”, the dominating architecture for hosting websites in the early 2000s. It’s still the most popular database, but it has declined a lot. Being bought by Sun and then Oracle didn’t do MySQL any favors. Neither did the free fork MariaDB, created by one of the MySQL founders.
- Postgres has always played second fiddle to MySQL. And that for a database that defines itself as the “the World’s Most Advanced Open Source Relational Database”! But Postgres does have the image of being more sophisticated than MySQL. What it does have for sure is the concept of extensions that can safely add new functionality.
- MongoDB is the most popular NoSQL database on this list.
- I don’t know much about Cassandra, Couchbase, and Neo4j, except that they are much less popular than MongoDB (and decreasing) and, besides Cassandra, are barely mentioned in job ads.
This is my recommendation:
- On your current project, keep your existing database unless that database is absolutely, irrevocably, really not working out for you.
- If you need to switch databases or are on a new project:
- If you know that you’ll need the NoSQL features and/or scalability, and you can’t get this with MySQL, then use MongoDB.
- Otherwise, use MySQL.