[Bug]: Fix Return Value for Non-Existent Collection,Partition,Index Drop

[nish112022]

Is there an existing issue for this?

• I have searched the existing issues

Environment

- Milvus version: 2.4.X
- Deployment mode(standalone or cluster):both
- MQ type(rocksmq, pulsar or kafka):    
- SDK version(e.g. pymilvus v2.0.0rc2):pymilvus 2.4.x
- OS(Ubuntu or CentOS): 
- CPU/Memory: 
- GPU: 
- Others:

Current Behavior

Currently in drop_collection_task.go

func (t *dropCollectionTask) Execute(ctx context.Context) error {
	// use max ts to check if latest collection exists.
	// we cannot handle case that
	// dropping collection with `ts1` but a collection exists in catalog with newer ts which is bigger than `ts1`.
	// fortunately, if ddls are promised to execute in sequence, then everything is OK. The `ts1` will always be latest.
	collMeta, err := t.core.meta.GetCollectionByName(ctx, t.Req.GetDbName(), t.Req.GetCollectionName(), typeutil.MaxTimestamp)
	if errors.Is(err, merr.ErrCollectionNotFound) {
		// make dropping collection idempotent.
		log.Warn("drop non-existent collection", zap.String("collection", t.Req.GetCollectionName()))
		return nil
	}

Similarly in drop_partition_task.go

	if partID == common.InvalidPartitionID {
		log.Warn("drop an non-existent partition", zap.String("collection", t.Req.GetCollectionName()), zap.String("partition", t.Req.GetPartitionName()))
		// make dropping partition idempotent.
		return nil
	}

and in index_service.go

	indexes := s.meta.indexMeta.GetIndexesForCollection(req.GetCollectionID(), req.GetIndexName())
	if len(indexes) == 0 {
		log.Info(fmt.Sprintf("there is no index on collection: %d with the index name: %s", req.CollectionID, req.IndexName))
		return merr.Success(), nil
	}

Expected Behavior

We should have proper mechanism to not execute the function any longer in these particular cases.Need to return appropriate values.

Steps To Reproduce

Whenever,these tasks are created in milvus.

Milvus Log

No response

Anything else?

No response

[yanliang567]

/assign @congqixia
please help to review the issue and pr
/unassign

[xiaofan-luan]

The ddl design of milvus followed idempotence.
which means drop an existing collection extra performed same as drop an non existing collection. So you can retry drop collection until it succeed when get error.
That's why we don't throw error on dropping on non existing collection