wangbo commented on pull request #3604:
URL: https://github.com/apache/incubator-doris/pull/3604#issuecomment-635401808
> > @morningman
> > The key point is that it's currently impossible to accurately estimate
the size of the memory footprint at runtime according to table size.Otherwise,
we can choose the right join mode or the correct num backends.
> > At present, it seems that it can only be adjusted manually. User decide
the join mode.
>
> So I think just use the `shuffle hint` is enough? No need to add new
config `HASH_TBL_SPACE_OVERHEAD` or disallow broadcast large than 100MB?
I think we can set ```partition join``` as default when we're unable to
estimate the cost accurately and broadcast join cost equals partition join cost
and without user hint.
From
```
&& broadcastCost <= partitionCost))) {
doBroadcast = true;
} else {
doBroadcast = false;
}
```
to
```
&& broadcastCost < partitionCost))) {
doBroadcast = true;
} else {
doBroadcast = false;
}
```
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