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Monitoring vector index capacity - Amazon DynamoDB

Monitoring vector index capacity

To monitor capacity consumption for vector index operations, set the ReturnConsumedCapacity parameter to INDEXES or TOTAL in your SearchVectors requests, or to INDEXES in your write API requests.

Vector index operations are metered in two units, separate from the read and write capacity units used by the base table:

  • Vector Search (VS) – The unit that meters SearchVectors operations. VS consumption is reported as VectorSearchRequestBytes and scales with the size of the vector data the search examines and returns.

  • Vector Write (VWR) – The unit that meters writes replicated into a vector index. VWR consumption is reported as VectorWriteRequestBytes and scales with the size of the data replicated to the index.

The following example shows the ConsumedCapacity returned by a SearchVectors request.

{
    "ConsumedCapacity": {
        "VectorSearchRequestBytes": 41714.0
    }
}

For write operations (PutItem, UpdateItem, DeleteItem, BatchWriteItem, TransactWriteItems), the response includes a VectorIndexes map in ConsumedCapacity, keyed by index name. Each entry reports VectorWriteRequestBytes for the capacity consumed when replicating changes to each vector index.

{
    "ConsumedCapacity": {
        "TableName": "Products",
        "CapacityUnits": 5.0,
        "Table": {
            "CapacityUnits": 5.0
        },
        "VectorIndexes": {
            "ProductEmbeddingIndex": {
                "VectorWriteRequestBytes": 4125.0
            }
        }
    }
}

Vector index capacity is metered in bytes processed, reported separately from base table read and write capacity. Use these fields to understand what drives your vector index cost:

  • Search cost (VectorSearchRequestBytes) scales primarily with the size of the vectors the search must examine, which grows with the number of dimensions in the index and the amount of data returned. Restricting a search to a single partition key value reduces the amount of data examined. Returning the vector attribute in results increases cost further because the response includes the full vector data.

  • Write cost (VectorWriteRequestBytes) is incurred each time you write, update, or delete an item that changes a vector-indexed attribute, and scales with the size of the data replicated to the index. Writes that do not change an indexed attribute do not incur vector write capacity.

Higher-dimensional embeddings increase both search and write cost because each vector carries more data. For current pricing, see the Amazon DynamoDB pricing on the AWS website.

DynamoDB also publishes vector index capacity to CloudWatch as the VectorSearchRequestBytes and VectorWriteRequestBytes metrics, dimensioned by TableName and VectorIndexName. Use these metrics to chart and alarm on vector index usage over time. For metric definitions, see VectorSearchRequestBytes and VectorWriteRequestBytes.