CBLVectorIndexConfiguration

@interface CBLVectorIndexConfiguration : CBLIndexConfiguration

ENTERPRISE EDITION ONLY

Configuration for creating vector indexes.

  • The SQL++ expression returning either a vector, which is an array of 32-bit floating-point numbers, or a Base64 string representing an array of 32-bit floating-point numbers in little-endian order.

    When lazy index is enabled, an expression will return a value for computing a vector lazily by using CBLIndexUpdater instead.

    Declaration

    Objective-C

    @property (nonatomic, readonly) NSString *_Nonnull expression;

  • The number of vector dimensions.

    Note

    The maximum number of vector dimensions supported is 4096.

    Declaration

    Objective-C

    @property (nonatomic, readonly) unsigned int dimensions;

  • The number of centroids which is the number buckets to partition the vectors in the index.

    Note

    The recommended number of centroids is the square root of the number of vectors to be indexed, and the maximum number of centroids supported is 64,000.

    Declaration

    Objective-C

    @property (nonatomic, readonly) unsigned int centroids;

  • Vector encoding type. The default value is 8-bits Scalar Quantizer.

    Declaration

    Objective-C

    @property (nonatomic) CBLVectorEncoding *_Nonnull encoding;

  • Distance Metric type. The default value is euclidean distance.

    Declaration

    Objective-C

    @property (nonatomic) int metric;

  • The minimum number of vectors for training the index. The default value is zero, meaning that minTrainingSize will be automatically calculated by the index based on the number of centroids specified, encoding types, and the encoding parameters.

    The training will occur at or before the APPROX_VECTOR_DISANCE query is executed, provided there is enough data at that time, and consequently, if training is triggered during a query, the query may take longer to return results.

    If a query is executed against the index before it is trained, a full scan of the vectors will be performed. If there are insufficient vectors in the database for training, a warning message will be logged, indicating the required number of vectors.

    Declaration

    Objective-C

    @property (nonatomic) unsigned int minTrainingSize;

  • The maximum number of vectors used for training the index. The default value is zero, meaning that the maxTrainingSize will be automatically calulated by the index based on the number of centroids specified, encoding types, and the encoding parameters.

    Declaration

    Objective-C

    @property (nonatomic) unsigned int maxTrainingSize;

  • The number of centroids that will be scanned during a query. The default value is zero, meaning that the numProbes will be automatically calulated by the index based on the number of centroids specified.

    Declaration

    Objective-C

    @property (nonatomic) unsigned int numProbes;

  • The boolean flag indicating that index is lazy or not. The default value is false.

    If the index is lazy, it will not be automatically updated when the documents in the collection are changed, except when the documents are deleted or purged.

    When configuring the index to be lazy, the expression set to the config is the expression that returns a value used for computing the vector.

    To update the lazy index, use a CBLIndexUpdater object obtained from a CBLQueryIndex object, which can be retrieved from a CBLCollection object.

    Declaration

    Objective-C

    @property (nonatomic) _Bool isLazy;

  • Initializes the CBLVectorIndexConfiguration object.

    Declaration

    Objective-C

    - (nonnull instancetype)initWithExpression:(nonnull NSString *)expression
                                dimensions:(unsigned int)dimensions
                                 centroids:(unsigned int)centroids;

    Parameters

    expression

    The SQL++ expression returning a vector which is an array of numbers.
    dimensions

    The number of dimensions of the vectors to be indexed. The vectors that do not have the same dimensions specified in the config will not be indexed. The dimensions must be >= 2 and <= 4096.
    centroids

    The number of centroids which is the number buckets to partition the vectors in the index. The number of centroids will be based on the expected number of vectors to be indexed; one suggested rule is to use the square root of the number of vectors. The centroids must be >= 1 and <= 64000.

    Return Value

    The CBLVectorIndexConfiguration object.