105 lines
3.9 KiB
Markdown
105 lines
3.9 KiB
Markdown
# CavalliumDB Engine
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[Reactive](https://www.reactive-streams.org/) database engine written in Java using [Project Reactor](https://github.com/reactor/reactor-core).
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This library provides a basic reactive abstraction and implementation of a **key-value store** and a **search engine**.
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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.
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## Key-value store implementations
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1. [RocksDB](https://github.com/facebook/rocksdb): A persistent key-value store for flash storage
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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
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## Search engine implementations
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1. Persistent [Lucene Core](https://github.com/apache/lucene) with custom sharding: Featureful and fast text search engine library
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2. In-memory temporary [Lucene Core](https://github.com/apache/lucene) instance: Useful for building and analyzing temporary indices
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## Extra features
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### Serializable search engine queries
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Queries can be serialized and deserialized using an efficient custom serialization format
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### Direct byte buffer
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The database abstraction can avoid copying the data multiple times by using RocksDB JNI and Netty 5 buffers
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### Declarative data records generator and versioned codecs
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A data generator that generates [Java 16 records](https://www.baeldung.com/java-record-keyword) is available:
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it allows you to generate custom records by defining the fields using a .yaml file.
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The generator also generates at compile time the source of specialized serializers,
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deserializers, and upgraders, for each custom record.
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The key-value store abstraction allows you to deserialize old versions of your data transparently, by using
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the custom upgraders and the custom deserializers automatically.
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The data generator can be found in the [Data generator](https://github.com/Cavallium/data-generator) repository.
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# Features
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- **RocksDB key-value store**
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- Snapshots
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- Multi-column database
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- Write-ahead log and corruption recovery
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- Multiple data types:
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- Single value (Singleton)
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- Map (Dictionary)
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- Composable nested map (Deep dictionary)
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- Customizable data serializers
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- Values codecs
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- Update-on-write value versioning using versioned codecs
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- **Apache Lucene Core indexing library**
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- Snapshots
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- Documents structure
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- Sorting
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- Ascending and descending
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- Numeric or non-numeric
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- Searching
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- Nested search terms
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- Combined search terms
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- Fuzzy text search
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- Coordinates, integers, longs, strings, text
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- Indicization and analysis
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- N-gram
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- Edge N-gram
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- English words
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- Stemming
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- Stopwords removal
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- Results filtering
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# F.A.Q.
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- **Why is it so difficult to use?**
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This is not a DBMS.
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This is an engine on which a DBMS can be built upon; for this reason it's very difficult to use directly without building another abstraction layer on top.
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- **Can I use objects instead of byte arrays?**
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Yes, you must serialize/deserialize them using a library of your choice.
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CodecSerializer allows you to implement versioned data using a codec for each data version.
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Note that it uses 1 to 4 bytes more for each value to store the version.
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- **Why there is a snapshot function for each database part?**
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Since RocksDB and lucene indices are different libraries, you can't take a snapshot of every database atomically.
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An universal snapshot must be implemented as a collection of each database snapshot.
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- **Is CavalliumDB Engine suitable for your project?**
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No.
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This engine is largely undocumented, and it doesn't provide extensive tests.
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# Examples
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In `src/example/java` you can find some *(ugly)* examples.
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