Fix flush deltabuf with segmentID=0 (#23064)

See also: #23062

Signed-off-by: yangxuan <xuan.yang@zilliz.com>

internal/datanode/buffer.go

@@ -142,6 +142,7 @@ func (bm *DelBufferManager) CompactSegBuf(compactedToSegID UniqueID, compactedFr
 	compactToDelBuff, loaded := bm.Load(compactedToSegID)
 	if !loaded {
 		compactToDelBuff = newDelDataBuf()
+		compactToDelBuff.item.segmentID = compactedToSegID
 	}
 
 	for _, segID := range compactedFromSegIDs {

internal/datanode/buffer_test.go

@@ -186,6 +186,11 @@ func Test_CompactSegBuff(t *testing.T) {
 	assert.False(t, seg2Exist)
 	assert.Equal(t, int64(2), delBufferManager.GetEntriesNum(compactedToSegID))
 
+	// test item of compactedToSegID is correct
+	compactTo, ok := delBufferManager.Load(compactedToSegID)
+	assert.True(t, ok)
+	assert.Equal(t, compactedToSegID, compactTo.item.segmentID)
+
 	//5. test roll and evict (https://github.com/milvus-io/milvus/issues/20501)
 	delBufferManager.channel.rollDeleteBuffer(compactedToSegID)
 	_, segCompactedToExist := delBufferManager.Load(compactedToSegID)