Open-Source Databases · sqlancer

sqlancer

SQLancer is an automated testing tool that finds logic and performance bugs in database systems by generating SQL statements and validating results through multiple test oracles. It has discovered hundreds of bugs in mature DBMSs and supports testing PostgreSQL, MySQL, MariaDB, SQLite, CockroachDB, TiDB, DuckDB, and H2.

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Source: GitHub — github.com/sqlancer/sqlancer

1.7k

GitHub stars

397

Forks

Java

Primary language

MIT

License (OSI-approved)

Key facts

Objective fields from the source. Values we can't verify are shown as “Unknown” rather than guessed.

Field	Value
Repository	sqlancer/sqlancer
Owner	sqlancer
Primary language	Java
License	MIT — OSI-approved
Stars	1.7k
Forks	397
Open issues	139
Latest release	v2.0.0 (2022-01-12)
Last updated	2026-06-21
Source	https://github.com/sqlancer/sqlancer

What sqlancer is

SQLancer combines feedback-guided SQL generation with complementary test oracles (TLP, NoREC, PQS, DQP, CODDTest, CERT) to detect logic bugs, performance issues, crashes, and internal errors in DBMS implementations. It operates as a Java-based fuzzing framework with configurable thread count, timeout, and reduction capabilities.

Quickstart

Get the sqlancer source

Clone the repository and explore it locally.

terminalbash

1git clone https://github.com/sqlancer/sqlancer.git2cd sqlancer3# follow the project's README for install & configuration

Need it deployed, integrated, or customized instead? DEV.co ships production installs.

Best use cases

Pre-release DBMS validation

Test custom or forked database implementations before production release to catch logic bugs that produce incorrect result sets or crash the system.

Database compatibility testing

Validate newly upgraded or migrated DBMS versions (PostgreSQL, MySQL, etc.) to ensure correctness across multiple test oracles before rolling out to production.

Research and academic DBMS development

Systematic bug detection for experimental or in-development database systems, particularly those implementing new query optimization or execution strategies.

Implementation considerations

Requires Java 11+ and Maven; build from source using `mvn package` or use pre-built Docker images from DockerHub (mrigger/sqlancer).
For server-based DBMSs (PostgreSQL, MySQL), must have DBMS instance running and accessible; embedded systems (SQLite, H2, DuckDB) run in-process.
Crashes in embedded DBMSs will crash the JVM; isolate testing in separate environments if system stability is critical.
Latest release is v2.0.0 from Jan 2022, but last push was June 2026; verify compatibility with your target DBMS version before relying on it.
Configure resource limits using `--num-threads`, `--timeout-seconds`, and `--num-tries` to control test duration and termination behavior.

When to avoid it — and what to weigh

Need immediate production bug fixes — SQLancer finds bugs but does not fix them. Projects must have resources to triage, reproduce, and patch issues independently.
Testing user-written queries rather than DBMS implementation — SQLancer targets logic bugs in database system code, not SQL syntax validation or query semantics for end-user applications.
Embedded systems with minimal Java footprint — Requires Java 11+ and Maven; not suitable for environments where JVM dependency or testing overhead is prohibitive.
Unsupported DBMS — Limited to PostgreSQL, MySQL, MariaDB, SQLite, CockroachDB, TiDB, DuckDB, and H2. Custom or proprietary databases not in this list are not supported.

License & commercial use

MIT License (permissive OSI-approved license). Allows commercial use, modification, and distribution with attribution.

MIT License permits commercial use without restriction. Suitable for closed-source database products or vendor-internal testing. No support obligations implied; commercial support not mentioned in repository.

DEV.co evaluation signals

Editorial assessment — not user reviews. Directional, with an explicit confidence level.

Signal	Assessment
Maintenance	Active
Documentation	Adequate
License clarity	Clear
Deployment complexity	Low
DEV.co fit	Good
Assessment confidence	High

Security considerations

SQLancer generates SQL to stress-test DBMSs; no security-specific claims made. When testing server DBMSs, ensure isolated network access and proper authentication. Embedded DBMS crashes propagate to JVM process, so run in sandboxed environments. No mention of fuzzing result sanitization or vulnerability disclosure protocols.

Alternatives to consider

pg_chaosmonkey / pgbench

PostgreSQL-specific tools for load testing and chaos engineering. Narrower scope than SQLancer but simpler for PostgreSQL-only environments.

sqlsmith (PostgreSQL extension)

Lightweight SQL fuzzing for PostgreSQL using grammar-based generation. Smaller footprint than SQLancer but lacks multi-oracle validation and cross-DBMS support.

propEr / QuickCheck (Erlang/Haskell)

Property-based testing frameworks for custom DBMS implementations. More flexible for non-SQL databases but require manual test oracle definition.

Software development agency

Build on sqlancer with DEV.co software developers

Use SQLancer to systematically test your DBMS for logic bugs before release. Get started with Java 11, Maven, and a quick build.

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sqlancer FAQ

Can SQLancer test my custom/proprietary database?

Only if you implement the DBMS interface. SQLancer has hand-written generators for PostgreSQL, MySQL, MariaDB, SQLite, CockroachDB, TiDB, DuckDB, and H2. Custom systems require adding a new implementation.

What do I do if SQLancer finds a bug?

SQLancer generates reproduction steps in logs. Use `--use-reducer` (experimental) or C-Reduce to minimize the test case, then manually verify the bug and report it to the DBMS maintainers. SQLancer does not fix bugs.

Why does SQLancer run indefinitely?

By default, SQLancer searches for bugs until manually stopped (Ctrl+C). Use `--num-tries` or `--timeout-seconds` to set a termination condition.

Is SQLancer suitable for continuous integration?

Yes, with caveats: use `--timeout-seconds` or `--num-tries` for CI gates. Embed log parsing to detect bugs automatically. Expect irregular run times and long execution; allocate resources accordingly.

Software developers & web developers for hire

DEV.co helps companies turn open-source tools like sqlancer into production software. Our software development services cover the full lifecycle — architecture, web development, integration, and maintenance — delivered by software developers and web developers who ship. Engage our software development agency to implement or customize it for your open-source databases stack.

Validate Your Database Implementation

Use SQLancer to systematically test your DBMS for logic bugs before release. Get started with Java 11, Maven, and a quick build.

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