[Bug]: The collections/flush api does not take effect after execution

[zhuwenxing]

Is there an existing issue for this?

• I have searched the existing issues

Environment

- Milvus version:master-20250123-f070af67-amd64
- Deployment mode(standalone or cluster):
- MQ type(rocksmq, pulsar or kafka):    
- SDK version(e.g. pymilvus v2.0.0rc2):
- OS(Ubuntu or CentOS): 
- CPU/Memory: 
- GPU: 
- Others:

Current Behavior

test code

    def test_collection_flush(self):
        """
        target: test collection flush
        method: create collection, insert data multiple times and flush
        expected: flush successfully
        """
        # Create collection
        name = gen_collection_name()
        client = self.collection_client
        vector_client = self.vector_client
        payload = {
            "collectionName": name,
            "schema": {
                "fields": [
                    {"fieldName": "book_id", "dataType": "Int64", "isPrimary": True, "elementTypeParams": {}},
                    {"fieldName": "my_vector", "dataType": "FloatVector", "elementTypeParams": {"dim": 128}}
                ]
            }
        }
        client.collection_create(payload)

        # Insert small batches of data multiple times
        for i in range(3):
            vectors = [gen_vector(dim=128) for _ in range(10)]
            insert_data = {
                "collectionName": name,
                "data": [
                    {
                        "book_id": i * 10 + j,
                        "my_vector": vector
                    }
                    for i, vector in enumerate(vectors)
                    for j in range(10)
                ]
            }
            response = vector_client.vector_insert(insert_data)
            assert response["code"] == 0
        c = Collection(name)
        num_entities_before_flush = c.num_entities
        # Flush collection
        response = client.flush(name)
        assert response["code"] == 0
        # check segments
        num_entities_after_flush = c.num_entities
        logger.info(f"num_entities_before_flush: {num_entities_before_flush}, num_entities_after_flush: {num_entities_after_flush}")
        # assert num_entities_after_flush > num_entities_before_flush
        c.flush()
        num_entities_after_flush = c.num_entities
        logger.info(f" num_entities_after_flush by pymilvus: {num_entities_after_flush}")

[2025-01-23 15:56:07 - DEBUG - urllib3.connectionpool]: http://10.104.21.108:19530 "POST /v2/vectordb/collections/flush HTTP/1.1" 200 20 (connectionpool.py:475)
[2025-01-23 15:56:07 - DEBUG - ci_test]: 
method: post, 
url: http://10.104.21.108:19530/v2/vectordb/collections/flush, 
cost time: 0.15013384819030762, 
header: {'Content-Type': 'application/json', 'Authorization': 'Bearer None', 'RequestId': '7ee4a1ee-d95f-11ef-9c14-acde48001122'}, 
payload: {
    "collectionName": "test_collection_2025_01_23_15_56_04_811858KhgpRpFk"
}, 
response: {"code":0,"data":{}} (milvus.py:80)
[2025-01-23 15:56:07 - INFO - ci_test]: num_entities_before_flush: 0, num_entities_after_flush: 0 (test_collection_operations.py:1609)
[2025-01-23 15:56:18 - INFO - ci_test]:  num_entities_after_flush by pymilvus: 300 (test_collection_operations.py:1613)

There are two points indicating that the flush interface is not actually executing:

The execution time is too short. Even for small data flush operations, it usually takes about 3 seconds, but the RESTful flush interface returns very quickly
Before and after the flush, the number of entities does not change to reflect the actual number of insertions

From the subsequent logs, we can see that using the flush interface through pymilvus can make the number of entities change to the actual number of inserted rows

Expected Behavior

No response

Steps To Reproduce

Milvus Log

No response

Anything else?

No response

[zhuwenxing]

/assign @smellthemoon

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.
Rotten issues close after 30d of inactivity. Reopen the issue with /reopen.

[zhuwenxing]

/assign @MrPresent-Han