xingtanzjr opened a new issue #8122:
URL: https://github.com/apache/incubator-doris/issues/8122
I am reading BE's code recently. For the data stream part, I think I get the
idea of Doris about how to exchange data steam between fragments in different
node. But I still have a question when I reading the code in
`data_stream_mgr.cpp`.
For the method `find_recvr()` in `data_stream_mgr.cpp`, it returns an new
object of `DataStreamRecvr` and doesn't put it in `DataStreamMgr`'s
`_receiver_map `. See the code snippet below.
```
shared_ptr<DataStreamRecvr> DataStreamMgr::find_recvr(const TUniqueId&
fragment_instance_id,
PlanNodeId node_id,
bool acquire_lock) {
VLOG_ROW << "looking up fragment_instance_id=" << fragment_instance_id
<< ", node=" << node_id;
size_t hash_value = get_hash_value(fragment_instance_id, node_id);
if (acquire_lock) {
_lock.lock();
}
std::pair<StreamMap::iterator, StreamMap::iterator> range =
_receiver_map.equal_range(hash_value);
while (range.first != range.second) {
shared_ptr<DataStreamRecvr> recvr = range.first->second;
if (recvr->fragment_instance_id() == fragment_instance_id &&
recvr->dest_node_id() == node_id) {
if (acquire_lock) {
_lock.unlock();
}
return recvr;
}
++range.first;
}
if (acquire_lock) {
_lock.unlock();
}
// QUESTION IS HERE: It return am empty DataSteamRecvr without put it in
_receiver_map
return shared_ptr<DataStreamRecvr>();
}
```
So, the question is... how the ExchangeNode find this DataSteamRecvr if it
is not put in the map.
I know it definitely works but I am confused about it. Can anyone answer
this question ?
Thanks,
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