STL_SORT

The STL_SORT index is an index type specifically designed to enhance query performance on numeric fields (INT8, INT16, etc.), VARCHAR fields, or TIMESTAMPTZ fields within Milvus by organizing the data in a sorted order.

Use the STL_SORT index if you frequently run queries with:

• Comparison filtering with ==, !=, >, <, >=, and <= operators

• Range filtering with IN and LIKE operators

Supported data types

• Numeric fields (e.g., INT8, INT16, INT32, INT64, FLOAT, DOUBLE). For details, refer to Boolean & Number.

• VARCHAR fields. For details, refer to String Field.

• TIMESTAMPTZ fields. For details, refer to TIMESTAMPTZ Field.

How it works

Milvus implements STL_SORT in two phases:

1. Build index

   • During ingestion, Milvus collects all values for the indexed field.

   • The values are sorted in ascending order using C++ STL’s std::sort.

   • Each value is paired with its entity ID, and the sorted array is persisted as the index.

2. Accelerate queries

   • At query time, Milvus uses binary search (std::lower_bound and std::upper_bound) on the sorted array.

   • For equality, Milvus quickly finds all matching values.

   • For ranges, Milvus locates the start and end positions and returns all values in between.

   • Matching entity IDs are passed to the query executor for final result assembly.

This reduces query complexity from O(n) (full scan) to O(log n + m), where m is the number of matches.

Create an STL_SORT index

You can create an STL_SORT index on a numeric or TIMESTAMPTZ field. No extra parameters are required.

The example below shows how to create an STL_SORT index on a TIMESTAMPTZ field:

from pymilvus import MilvusClient

client = MilvusClient(uri="http://localhost:19530") # Replace with your server address

# Assume you have defined a TIMESTAMPTZ field named "tsz" in your collection schema

# Prepare index parameters
index_params = client.prepare_index_params()

# Add RTREE index on the "tsz" field
index_params.add_index(
    field_name="tsz",
    index_type="STL_SORT",   # Index for TIMESTAMPTZ
    index_name="tsz_index",  # Optional, name your index
    params={}                # No extra params needed
)

# Create the index on the collection
client.create_index(
    collection_name="tsz_demo",
    index_params=index_params
)

Drop an index

Use the drop_index() method to remove an existing index from a collection.

client.drop_index(
    collection_name="tsz_demo",   # Name of the collection
    index_name="tsz_index" # Name of the index to drop
)

Usage notes

• Field types: Works with numeric and TIMESTAMPTZ fields. For more information on data types, refer to Boolean & Number and TIMESTAMPTZ Field.

• Parameters: No index parameters are needed.

• Mmap not supported: Memory-mapped mode is not available for STL_SORT.