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CavalliumDB Engine
==================
# CavalliumDB Engine
![Maven Package](https://github.com/Cavallium/CavalliumDBEngine/workflows/Maven%20Package/badge.svg)
A very simple reactive wrapper for RocksDB and Lucene.
[Reactive](https://www.reactive-streams.org/) database engine written in Java using [Project Reactor](https://github.com/reactor/reactor-core).
This is not a database, but only a wrapper for Lucene Core and RocksDB, with a bit of abstraction.
This library provides a basic reactive abstraction and implementation of a **key-value store** and a **search engine**.
Four implementations exists out-of-the-box, two for the key-value store, two for the search engine, but it's possible to add more implementations.
## Key-value store implementations
1. [RocksDB](https://github.com/facebook/rocksdb): A persistent key-value store for flash storage
3. [ConcurrentSkipListMap](https://docs.oracle.com/en/java/javase/16/docs/api/java.base/java/util/concurrent/ConcurrentSkipListMap.html): A concurrent in-memory key-value store
## Search engine implementations
1. Persistent [Lucene Core](https://github.com/apache/lucene) with custom sharding: One of the featureful and fastest text search engine libraries in the world
2. In-memory temporary [Lucene Core](https://github.com/apache/lucene) instance: Useful for building and analyzing temporary indices
## Extra features
### Serializable search engine queries
Queries can be serialized and deserialized using an efficient custom serialization format
### Direct byte buffer
The database abstraction can avoid copying the data multiple times by using RocksDB JNI and Netty 5 buffers
### Declarative data records generator and versioned codecs
A data generator that generates [Java 16 records](https://www.baeldung.com/java-record-keyword) is available:
it allows you to generate custom records by defining the fields using a .yaml file.
The generator also generates at compile time the source of specialized serializers,
deserializers, and upgraders, for each custom record.
The key-value store abstraction allows you to deserialize old versions of your data transparently, by using
the custom upgraders and the custom deserializers automatically.
The data generator can be found in the [Data generator](https://github.com/Cavallium/data-generator) repository.
# Features
- **RocksDB key-value database engine**
- **RocksDB key-value store**
- Snapshots
- Multi-column database
- Write-ahead log and corruption recovery
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- **Why there is a snapshot function for each database part?**
Since RocksDB and lucene indices are different software, you can't take a snapshot of everything in the same instant.
Since RocksDB and lucene indices are different libraries, you can't take a snapshot of every database atomically.
A single snapshot must be implemented as a collection of all the snapshots.
An universal snapshot must be implemented as a collection of each database snapshot.
- **Is CavalliumDB Engine suitable for your project?**
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# Examples
In `src/example/java` you can find some quick implementations of each core feature.
In `src/example/java` you can find some *(ugly)* examples.