platoneko commented on code in PR #13993:
URL: https://github.com/apache/doris/pull/13993#discussion_r1015506921
##########
be/src/olap/rowset/rowset_meta.h:
##########
@@ -53,12 +53,14 @@ class RowsetMeta {
}
virtual bool init_from_pb(const RowsetMetaPB& rowset_meta_pb) {
- _rowset_meta_pb = rowset_meta_pb;
- if (_rowset_meta_pb.has_tablet_schema()) {
+ if (rowset_meta_pb.has_tablet_schema()) {
_schema = TabletSchemaCache::instance()->insert(
- _rowset_meta_pb.tablet_schema().SerializeAsString());
- _rowset_meta_pb.clear_tablet_schema();
+ rowset_meta_pb.tablet_schema().SerializeAsString());
}
+ auto& mut_rowset_meta_pb = const_cast<RowsetMetaPB&>(rowset_meta_pb);
Review Comment:
This is a trick to reduce unnecessary memory allocation and release
overhead. A common solution to release TabletSchemaPB memory is:
```c++
_rowset_meta_pb = rowset_meta_pb;
_rowset_meta_pb.set_allocated_tablet_schema(nullptr); // release
TabletSchemaPB
```
However, here we copy TabletSchemaPB from `rowset_meta_pb` to
`_rowset_meta_pb` but release it right away.
Another more efficient way: release ownership of TabletSchemaPB from
`rowset_meta_pb` and then set it back to `rowset_meta_pb`, this won't break
const semantics of `rowset_meta_pb`, because `rowset_meta_pb` is not changed
before and after call this method.
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