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Chroma

https://www.trychroma.com/

Maven Dependency​

<dependency>
    <groupId>dev.langchain4j</groupId>
    <artifactId>langchain4j-chroma</artifactId>
    <version>1.19.0-beta29</version>
</dependency>

APIs​

  • ChromaEmbeddingStore

Examples​

Supported API Versions​

Chroma has multiple REST API versions:

  • until version 0.5.16: only API V1 is supported
  • versions 0.5.16 to 0.6.3: API V1 and V2 are supported (there are some bugs in V1 API introduced around 0.6.2)
  • versions after 0.7.0: only API V2 is supported, so you need to select the proper version when configuring the ChromaEmbeddingStore:
ChromaEmbeddingStore.builder()
    .apiVersion(ChromaApiVersion.V2)
    .baseUrl(...)
    .tenantName(...)
    .databaseName(...)
    .collectionName(...)
    .build();

Distance Metric​

A Chroma collection is created with a distance metric, which determines how the distance between two embeddings is measured. Chroma supports cosine, l2 (squared euclidean) and ip (inner product), and uses l2 unless another metric is requested.

When ChromaEmbeddingStore creates a collection, it creates it with the cosine distance metric. When the collection already exists, it is used as is, whichever distance metric it was created with:

ChromaEmbeddingStore store = ChromaEmbeddingStore.builder()
    .baseUrl("http://localhost:8000")
    .collectionName("my-collection")
    .build();

The relevance score returned by EmbeddingMatch.score() is always in the [0, 1] range, where 1 means the most relevant. It is derived from the distance metric of the collection, so scores obtained from collections with different distance metrics are not comparable with each other. The same applies to the minScore of an EmbeddingSearchRequest, which is compared against the score of the collection's own metric.

For ip, the score is accurate only if the embeddings are normalized, which is the case for most embedding models.

Current Limitations​

  • Chroma cannot filter by greater and less than of alphanumeric metadata, only int and float are supported
  • Chroma filters by not as following: if you filter by "key" not equals "a", then in fact all items with "key" != "a" value are returned, but no items without "key" metadata!