OSS Database Comparison: Best Open Source Databases 2026
An OSS database (open source database) is a database whose source code is published under an OSI-approved license, so you can run, modify and self-host it without paying a vendor. The most popular OSS databases in 2026 are PostgreSQL, MySQL and SQLite for relational data, Valkey and Redis for caching, ClickHouse and DuckDB for analytics, and Cassandra for very large write-heavy workloads. For most new applications the default choice is PostgreSQL. It was used by 55.6% of developers in the 2025 Stack Overflow Developer Survey, ahead of MySQL (40.5%) and SQLite (37.5%).
One trap to know before comparing: several well-known "open source" databases are not open source under the OSI definition anymore. The licensing section below covers which ones.
OSS database list: the main options compared
| Database | Type | License | Current version (October 2026) | Best for |
|---|---|---|---|---|
| PostgreSQL | Relational (SQL) | PostgreSQL License (permissive) | 18 (19 in beta) | General-purpose apps, JSON, geospatial, vectors |
| MySQL Community | Relational | GPLv2 | 9.7 LTS, 8.4 LTS | Web apps, read-heavy workloads, existing LAMP stacks |
| MariaDB | Relational (MySQL fork) | GPLv2 | 12.3 LTS | Drop-in MySQL replacement, community-governed |
| SQLite | Embedded relational | Public domain | 3.x | Mobile, desktop, edge, tests, single-server apps |
| Valkey | Key-value (in-memory) | BSD 3-Clause | 9.x | Caching, sessions, queues, rate limiting |
| ClickHouse | Columnar OLAP | Apache 2.0 | Monthly releases | Real-time analytics on billions of rows |
| DuckDB | Embedded columnar OLAP | MIT | Frequent releases | Local analytics on Parquet and CSV, notebooks |
| Apache Cassandra | Wide-column NoSQL | Apache 2.0 | 5.0 | Multi-region, write-heavy, always-on systems |
Versions as of October 2026: PostgreSQL 19 reached Beta 4 on September 24, 2026, so 18 is the current stable major (PostgreSQL news). MySQL now has two LTS lines (8.4 and 9.7) plus calendar-versioned Innovation releases starting with 26.7. MariaDB ships a new LTS every May, and 12.3 is the latest.
Relational OSS databases
PostgreSQL
PostgreSQL is the safest default. It has strict SQL standards compliance, transactional DDL, rich types (jsonb, arrays, ranges) and an extension ecosystem that covers most "do I need another database?" cases: PostGIS for geospatial, pgvector for embeddings, TimescaleDB for time series. The trade-off is operational. You need to understand vacuum, connection limits (put a pooler such as PgBouncer in front of many short-lived connections) and major-version upgrades.
Try it in 30 seconds with Docker. Note that from the PostgreSQL 18 image onward the volume mount point is /var/lib/postgresql, not /var/lib/postgresql/data as in older tutorials (Docker Hub: postgres):
docker run -d --name pg \
-e POSTGRES_PASSWORD=devpassword \
-p 5432:5432 \
-v pgdata18:/var/lib/postgresql \
postgres:18
docker exec -it pg psql -U postgres -c "select version();"
If you don't want to run it yourself, managed Postgres platforms such as Supabase add auth, storage and an auto-generated REST API. Our Supabase REST API quickstart shows that in practice.
MySQL and MariaDB
MySQL is still the most common database behind PHP and WordPress hosting, and it's fast for simple, read-heavy queries. The Community Edition is GPL. Some features, such as the thread pool and enterprise backup, are only in Oracle's commercial editions. For new installs, pick an LTS line (9.7 or 8.4) unless you specifically want the quarterly Innovation releases.
MariaDB started as a fork of MySQL and is governed by the MariaDB Foundation. It's mostly compatible with MySQL clients and SQL, but the two have diverged (JSON handling, replication, optimizer features), so test before you treat one as a drop-in for the other.
SQLite
SQLite isn't a server. It's a library that stores the whole database in one file. That makes it the right answer for mobile apps, desktop apps, CLI tools, tests and many single-server web apps. Its limit is concurrency: it allows one writer at a time. WAL mode helps a lot, but if several servers need to write to the same data, use PostgreSQL.
NoSQL and analytics OSS databases
Valkey (and Redis)
Valkey is the Linux Foundation fork of Redis 7.2.4, created after Redis left the BSD license in 2024. It speaks the same protocol, so existing Redis clients work. Use it as a cache, session store, queue or rate limiter. Don't use it as your only source of truth unless you understand its persistence options.
ClickHouse and DuckDB (open source OLAP)
If you searched "what is ClickHouse database": it's a columnar database built for analytics. It stores data by column and is built to aggregate very large tables quickly, which makes it a common open source data warehouse choice for event data, logs and product analytics. DuckDB fills the same role in-process: pip install duckdb and query Parquet files on your laptop with SQL, with no server at all.
-- DuckDB: query a Parquet file directly
SELECT country, count(*) AS signups
FROM 'events.parquet'
WHERE event = 'signup'
GROUP BY country
ORDER BY signups DESC;
Neither one replaces a transactional database. They're bad at frequent single-row updates.
Apache Cassandra
Cassandra is for data that must stay writable across multiple regions with no single point of failure. You model tables around your queries rather than normalizing, and you give up joins and ad-hoc queries. Most teams don't need it. The ones that do usually know it.
Licensing: which "open source" databases aren't
Check the license before you build on a database, especially if you offer it as part of a hosted service.
- MongoDB is licensed under the SSPL, which the OSI does not consider open source. MongoDB's own FAQ says so (MongoDB SSPL FAQ). It's free to self-host for your own app, but offering it as a service triggers the SSPL's obligations.
- Redis 8.0 and later is tri-licensed under RSALv2, SSPLv1 or AGPLv3. Only the AGPLv3 option is OSI open source (Redis licenses). If you want a permissive license, use Valkey.
- CockroachDB retired its free Core edition with version 24.3 in November 2024. It now ships only a source-available Enterprise license, free for companies under $10 million in annual revenue (Cockroach Labs).
Open source vs commercial databases
| OSS database | Commercial (Oracle, SQL Server, Snowflake) | |
|---|---|---|
| License cost | None | Per core, per user or per usage |
| Support | Community, or paid from vendors and cloud providers | Included with the contract |
| Lock-in | Low: standard SQL, many hosts | Higher: proprietary features and tooling |
| Enterprise features | Often via extensions or paid add-ons | Built in (advanced auditing, some HA modes) |
Oracle still tops DB-Engines' popularity ranking, but nearly every cloud provider sells managed PostgreSQL and MySQL. Running an OSS database no longer means running it yourself. Browse more options in DevHunt's database tools, or see free Firebase alternatives if you want a backend on top of an OSS database.
How to choose
- Building a typical web or mobile backend? PostgreSQL.
- Inheriting a PHP/WordPress stack or MySQL expertise? MySQL or MariaDB.
- Single process, single file, or on-device? SQLite.
- Need a cache or job queue next to your main database? Valkey.
- Analytics over large event or log data? ClickHouse on a server, DuckDB locally.
- Multi-region writes at very large scale? Cassandra, after confirming PostgreSQL with read replicas really isn't enough.
Start with one database and add a second only when a measured need appears. Most "we need NoSQL" decisions disappear once you use PostgreSQL's jsonb and proper indexes.
FAQ
What is an OSS database?
A database released under an open source license approved by the Open Source Initiative, such as the PostgreSQL License, GPL, Apache 2.0, MIT or BSD. You can read the code, self-host it and modify it. "Source-available" licenses like SSPL and RSAL don't qualify.
What are examples of open source databases?
PostgreSQL, MySQL Community, MariaDB, SQLite, Valkey, ClickHouse, DuckDB and Apache Cassandra. Redis is open source only under its AGPLv3 option (8.0 and later).
Which is the most popular open source database?
By developer usage, PostgreSQL: 55.6% of respondents in the 2025 Stack Overflow survey, followed by MySQL and SQLite. On the DB-Engines popularity ranking, MySQL is the top open source system, behind the commercial Oracle.
What is the world's most advanced open source database?
That's PostgreSQL's own tagline, and it's a fair description of its feature set: extensibility, standards compliance, and advanced indexing such as GIN, GiST and BRIN.
What's the best open source data warehouse or OLAP database?
ClickHouse for a server-based, real-time analytics warehouse. DuckDB for embedded analytics on files. Both are permissively licensed (Apache 2.0 and MIT).