* #1827 Combine request target vectors exceed max nq
Signed-off-by: Ngroot <yihua.mo@zilliz.com>

* refine dbimpl
Signed-off-by: Ngroot <yihua.mo@zilliz.com>

* refine dbimpl
Signed-off-by: Ngroot <yihua.mo@zilliz.com>

* fix unittest failure
Signed-off-by: Ngroot <yihua.mo@zilliz.com>
Co-authored-by: NJin Hai <hai.jin@zilliz.com>