[Bug]: REST API v2 `entities/search` accepts `group_size=0` and `-1` (gRPC rejects as "negative")

[yihui504]

Is there an existing issue for this?

• I have searched the existing issues

Environment

- Milvus version: v3.0.0 (release 2026-07-29, commit f46a0328558be155d11266a1a2b90602ccc9b366)
- Deployment mode: standalone (Docker, `milvusdb/milvus:v3.0.0`)
- MQ type: N/A
- SDK version: REST API v2 only (curl). pymilvus used for gRPC comparison.
- OS: Windows 11 (Docker Desktop)
- CPU/Memory: N/A
- GPU: None

Current Behavior

The REST API v2 POST /v2/vectordb/entities/search endpoint accepts groupSize=0 and groupSize=-1 in groupParams without validation (code: 0). The gRPC path correctly rejects both:

gRPC: code=1100, message="input group size:0 is negative, failed to do search_groupby"
gRPC: code=1100, message="input group size:-1 is negative, failed to do search_groupby"

The Grouping Search documentation states:

"By default, Grouping Search returns only one entity per group. If you want to increase the number of results to return per group, you can control this with the group_size and strict_group_size parameters."

This implies group_size is a positive integer that "increases" results per group — 0 and -1 are semantically meaningless.

Expected Behavior

groupSize should be validated as ≥ 1. REST should reject 0 and negative values with an explicit error, consistent with gRPC.

Steps To Reproduce

# 1. Create + load collection
curl -X POST http://localhost:19530/v2/vectordb/collections/create \
  -H "Content-Type: application/json" \
  -d '{"collectionName":"test_gs","dimension":4}'

# Insert data with "cat" field
for i in $(seq 0 9); do
  curl -X POST http://localhost:19530/v2/vectordb/entities/insert \
    -H "Content-Type: application/json" \
    -d "{\"collectionName\":\"test_gs\",\"data\":[{\"id\":$i,\"vector\":[0.$i,0.$i,0.$i,0.$i],\"cat\":$((i%3))}]}"
done

# 2. Search with groupSize=0 (bug)
curl -X POST http://localhost:19530/v2/vectordb/entities/search \
  -H "Content-Type: application/json" \
  -d '{"collectionName":"test_gs","data":[[0.5,0.5,0.5,0.5]],"limit":5,"groupParams":{"groupByField":"cat","groupSize":0}}'
# Response: {"code":0,...} — accepted (should be rejected)

# 3. Search with groupSize=-1 (bug)
curl -X POST http://localhost:19530/v2/vectordb/entities/search \
  -H "Content-Type: application/json" \
  -d '{"collectionName":"test_gs","data":[[0.5,0.5,0.5,0.5]],"limit":5,"groupParams":{"groupByField":"cat","groupSize":-1}}'
# Response: {"code":0,...} — accepted (should be rejected)

# 4. gRPC comparison
python -c "
from pymilvus import MilvusClient
mc = MilvusClient(uri='http://localhost:19530')
mc.search('test_gs', [[0.5]*4], limit=5, group_by_field='cat', group_size=0)
# → MilvusException: code=1100, 'input group size:0 is negative'
"

Milvus Log

REST v2 path (accepted - no error logged):

[2026/08/07 14:14:50.755 Z] [GIN] [/v2/vectordb/entities/search] [traceID=8eec52baf553ea87289e8c437d18ef92] [code=200] [latency=4.183428ms] [client=172.18.0.1] [method=POST] [error=]

Note the empty [error=] field - the REST path treats the invalid input as successful.

gRPC path (correctly rejected - pymilvus raises client-side):

<MilvusException: code=1100, message="input group size:0 is negative">

Run docker logs milvus-standalone for full logs.

Anything else?

• Grouping Search docs: group_size controls "number of results to return per group" — implies positive integer
• gRPC path validates at SearchGroupByOperator — REST v2 path skips this validation

[yanliang567]

Triage verification (2026-08-09): the request should use top-level groupingField, groupSize, and strictGroupSize instead of groupParams. With the corrected payload, explicit groupSize values 0 and -1 are still accepted. The REST handler forwards groupSize only when it is greater than 0, so downstream validation is bypassed and the default size is used. Confirmed RESTful API bug related to #36146 and #36908.