Getting Started with SWI-Prolog RocksDB on Windows 11

EricGT · December 24, 2025, 5:31pm

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Wiki Discussion: Getting Started with SWI-Prolog RocksDB on Windows 11

Getting Started with SWI-Prolog RocksDB on Windows 11

December 24, 2025

A beginner’s guide to installing and using RocksDB with SWI-Prolog on Windows 11.

What is This?

RocksDB is a high-performance database that stores information as key-value pairs. Think of it like a very fast filing cabinet where you can store and retrieve data.

SWI-Prolog is a programming language particularly good at working with logical rules and relationships.

rocks-predicates lets you store Prolog facts (like “John is a person” or “Paris is in France”) in RocksDB so they survive even after you close your program.

Key Benefit: Not Limited by RAM

Unlike regular Prolog which keeps everything in RAM (memory), RocksDB stores data on your hard drive, SSD, or even USB flash drives. This means:

No RAM limits: Store millions or billions of facts without running out of memory
Persistent storage: Data survives computer restarts and power loss
Flexible storage: Use fast SSDs for speed, or USB drives for portability
Trade-off: Hard drive access is slower than RAM, but RocksDB is optimized to be very fast (queries in microseconds)

Think of it like the difference between keeping notes in your head (RAM) versus writing them in a notebook (disk). The notebook can hold far more information, though accessing it takes slightly longer.

Why MSYS2?

Currently, RocksDB doesn’t work with native Windows SWI-Prolog. We need MSYS2, which provides a Linux-like environment on Windows where we can compile and run RocksDB.

Prerequisites

Windows 11 (this guide is specifically for Windows 11)
About 2 GB of free disk space
Administrator access to install software
About 30-45 minutes of time

Step 1: Install MSYS2

MSYS2 provides the environment we need to run RocksDB.

Download MSYS2
- Open your web browser
- Go to: https://www.msys2.org/
- Click the big download button
- Save the installer (it’s called something like msys2-x86_64-*.exe)
Run the Installer
- Double-click the downloaded file
- Click “Next” through the installer
- Use the default installation path: C:\msys64
- Click “Finish”
Update MSYS2
- After installation, a terminal window opens automatically
- Type this command and press Enter:
```
pacman -Syu
```
- When it asks “Proceed with installation? [Y/n]”, type Y and press Enter
- If it says to close the terminal, close it and reopen it from the Start menu (search for “MSYS2 MSYS”)
- Run the update command again:
```
pacman -Syu
```

Step 2: Install Required Tools

Now we’ll install the tools needed to build RocksDB.

Close the MSYS2 MSYS terminal if it’s open
Open MSYS2 MINGW64 (this is important - not the regular MSYS2)
- Press the Windows key
- Search for “MSYS2 MINGW64”
- Click to open it
- You should see a purple/blue terminal window
Install Git (needed to download code)
```
pacman -S git
```
- When asked “Proceed with installation? [Y/n]”, type Y and press Enter
Install the C++ Compiler
```
pacman -S mingw-w64-x86_64-gcc
```
- Type Y when prompted
Install RocksDB Library
```
pacman -S mingw-w64-x86_64-rocksdb
```
- Type Y when prompted
Install SWI-Prolog for MSYS2
```
pacman -S mingw-w64-x86_64-swi-prolog
```
- Type Y when prompted
Verify SWI-Prolog Installed
```
swipl --version
```
- You should see something like “SWI-Prolog version 10.0.0”

Step 3: Build the RocksDB Interface

Now we need to build the connection between SWI-Prolog and RocksDB.

Download the RocksDB Pack

cd ~
git clone https://github.com/JanWielemaker/rocksdb.git
cd rocksdb

Fix Compatibility Issues

The code needs two small fixes for newer RocksDB. Run these commands:

sed -i '1044s/.*/               true; } ),  \/\/ random_access_max_buffer_size removed in newer RocksDB/' cpp/rocksdb4pl.cpp

sed -i '1084s/.*/               true; } ),  \/\/ fail_if_options_file_error removed in newer RocksDB/' cpp/rocksdb4pl.cpp

Create Output Directory
```
mkdir -p lib/x64-win64
```

Compile the Interface

Copy and paste this entire command (it’s long):

g++ -shared -D__SWI_PROLOG__ -I/mingw64/lib/swipl/include \
    cpp/rocksdb4pl.cpp /mingw64/lib/librocksdb.a \
    -L/mingw64/lib/swipl/lib/x64-win64 -lswipl \
    -lsnappy -lzstd -lz -llz4 -lbz2 -lshlwapi -lrpcrt4 \
    -o lib/x64-win64/rocksdb4pl.dll

This will take about 30 seconds to 1 minute
If successful, you won’t see any error messages

Install to SWI-Prolog Pack Directory

mkdir -p ~/.local/share/swi-prolog/pack/rocksdb/lib/x64-win64
cp lib/x64-win64/rocksdb4pl.dll ~/.local/share/swi-prolog/pack/rocksdb/lib/x64-win64/

Step 4: Test Basic RocksDB

Let’s verify RocksDB works!

Start SWI-Prolog
```
swipl
```
- You should see a ?- prompt
Load RocksDB
```
?- use_module(library(rocksdb)).
```
- Expected result: true.
Test Basic Operations

Run these commands one at a time:
```
?- rocks_open('test.db', DB, []).
?- rocks_put(DB, foo, bar).
?- rocks_get(DB, foo, V).
?- rocks_close(DB).
```
Expected results:
- rocks_open → Shows DB = <rocksdb>(...)
- rocks_put → Shows true.
- rocks_get → Shows V = bar.
- rocks_close → Shows true.
Exit SWI-Prolog
```
?- halt.
```

Step 5: Install rocks-predicates

This gives you a way to store Prolog facts persistently.

Download rocks-predicates

cd ~
git clone https://github.com/JanWielemaker/rocks-predicates.git
cd rocks-predicates

Create Database Directory
```
mkdir -p dbs
```
Start SWI-Prolog
```
swipl
```
Load the Libraries
```
?- use_module(library(rocksdb)).
?- consult('rocks_preds.pl').
```
- You may see a warning about “ensure_directory” - this is normal and safe to ignore

Test Storing Data

Run these commands:

?- rdb_open('dbs/test_preds', DB).
?- rdb_assertz('dbs/test_preds', person(john)).
?- rdb_assertz('dbs/test_preds', person(mary)).
?- rdb_clause('dbs/test_preds', person(X), Body).

Expected results:

rdb_open → Shows DB = <rocksdb>(...)
Both rdb_assertz → Show true.

rdb_clause → Shows:

X = john,
Body = true ;
X = mary,
Body = true.

Common Commands Reference

Opening a Database

?- rdb_open('dbs/my_database', DB).

Storing Facts

?- rdb_assertz('dbs/my_database', parent(tom, bob)).
?- rdb_assertz('dbs/my_database', parent(bob, alice)).

Querying Facts

?- rdb_clause('dbs/my_database', parent(X, Y), Body).

This will show all parent relationships.

Closing a Database

?- rdb_close('dbs/my_database').

Storing Databases on Different Drives

Since RocksDB stores data on disk (not in RAM), you can put databases anywhere:

On Your Main Hard Drive

?- rdb_open('C:/data/my_database', DB).

On an External USB Drive

?- rdb_open('E:/portable_data/my_database', DB).

On a Network Drive

?- rdb_open('Z:/shared/my_database', DB).

Performance Tips:

SSD drives: Fastest option for frequent queries
Regular hard drives: Slower but fine for occasional access
USB flash drives: Portable but slowest; good for backups or moving data between computers
Network drives: Convenient for sharing but speed depends on network connection

Troubleshooting

“bash: git: command not found”

Solution: Install git:

pacman -S git

“cannot open output file lib/x64-win64/rocksdb4pl.dll”

Solution: Create the directory first:

mkdir -p lib/x64-win64

“The specified module could not be found”

Solution: Make sure you copied the DLL to the pack directory:

mkdir -p ~/.local/share/swi-prolog/pack/rocksdb/lib/x64-win64
cp lib/x64-win64/rocksdb4pl.dll ~/.local/share/swi-prolog/pack/rocksdb/lib/x64-win64/

Missing rocksdb4pl.dll when running rocks_open

Symptoms:
When running rocks_open('test.db', DB, []), you get an error like:

ERROR: Initialization goal raised exception:
ERROR: The specified module could not be found.
ERROR: Exported procedure rocksdb:rocks_open_/3 is not defined

Cause: The rocksdb4pl.dll file is missing from the expected location.

How to verify the DLL location:
You can check where SWI-Prolog expects to find the DLL:

?- absolute_file_name(foreign(rocksdb4pl), Path, [file_type(executable), access(exist)]).

This will show the expected path, typically:

~/.local/share/swi-prolog/pack/rocksdb/lib/x64-win64/rocksdb4pl.dll

Solution:

Make sure you completed Step 3, substep 5 from the installation instructions:

mkdir -p ~/.local/share/swi-prolog/pack/rocksdb/lib/x64-win64
cp lib/x64-win64/rocksdb4pl.dll ~/.local/share/swi-prolog/pack/rocksdb/lib/x64-win64/

Verify the DLL exists:

ls -lh ~/.local/share/swi-prolog/pack/rocksdb/lib/x64-win64/rocksdb4pl.dll

“Unknown procedure: rdb_open/2”

Solution: Make sure you loaded both libraries:

?- use_module(library(rocksdb)).
?- consult('rocks_preds.pl').

Wrong Terminal Type

Make sure you’re using MSYS2 MINGW64 (purple/blue terminal), not “MSYS2 MSYS” (yellow terminal).

What’s Next?

Now that you have RocksDB working, you can:

Store large amounts of data - RocksDB can handle millions of facts efficiently
Persist data across sessions - Unlike regular Prolog, your data survives when you close the program
Index your data - Use rdb_index/3 to make queries faster on large datasets
Use external storage - Put databases on USB drives or network drives for portability

Performance Examples

According to the rocks-predicates README (tested on AMD3950X with SSD):

Dataset	Facts	Load Time	Query Time	Database Size
WordNet 3.0	821,492 clauses	11.7 sec	10 microseconds	99 MB
Geonames RDF	123 million triples	35 minutes	30 microseconds	5.2 GB

What this means:

You can store millions of facts without running out of RAM
Queries are still very fast (microseconds)
The data is persistently saved on disk

Future: Native Windows Support

Currently, this setup requires MSYS2. There’s a potential path to native Windows support using vcpkg (Microsoft’s C++ package manager). This would eliminate the need for MSYS2 but requires modifying the rocksdb pack.

Getting Help

If you encounter issues:

Check the Troubleshooting section above
Visit the SWI-Prolog Discourse: https://swi-prolog.discourse.group/
Check the rocksdb pack page: "rocksdb" pack for SWI-Prolog
Open an issue on GitHub: GitHub - JanWielemaker/rocksdb: SWI-Prolog interface for RocksDB

Credits

RocksDB Pack: Jan Wielemaker
rocks-predicates: Jan Wielemaker
MSYS2 Integration: mgondan - Discourse forum - msys2
This Guide: Based on successful Windows 11 installation (December 2025)

License

This guide is provided as-is for educational purposes. The software packages mentioned have their own licenses:

RocksDB: GPL-2.0-only OR Apache-2.0
SWI-Prolog: BSD-2-Clause
MSYS2: Various open source licenses

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Getting Started with SWI-Prolog RocksDB on Windows 11

Getting Started with SWI-Prolog RocksDB on Windows 11

What is This?

Key Benefit: Not Limited by RAM

Why MSYS2?

Prerequisites

Step 1: Install MSYS2

Step 2: Install Required Tools

Step 3: Build the RocksDB Interface

Step 4: Test Basic RocksDB

Step 5: Install rocks-predicates

Common Commands Reference

Opening a Database

Storing Facts

Querying Facts

Closing a Database

Storing Databases on Different Drives

On Your Main Hard Drive

On an External USB Drive

On a Network Drive

Troubleshooting

“bash: git: command not found”

“cannot open output file lib/x64-win64/rocksdb4pl.dll”

“The specified module could not be found”

Missing rocksdb4pl.dll when running rocks_open

“Unknown procedure: rdb_open/2”

Wrong Terminal Type

What’s Next?

Performance Examples

Future: Native Windows Support

Getting Help

Credits

License

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