github-actions[bot] commented on code in PR #68018:
URL: https://github.com/apache/doris/pull/68018#discussion_r4032777651
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be/src/storage/segment/column_reader.h:
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@@ -1097,6 +1103,18 @@ class ConstantColumnReader : public ColumnReader {
Status get_segment_zone_map(segment_v2::ZoneMap* zone_map) const override;
+ // This reader serves a value the caller supplied, so the on-disk index
for the column describes
+ // something else: for a placeholder column it indexes the placeholder.
Leaving the iterator
+ // unset makes the caller fall back to reading through this reader, the
same as the path that
+ // finds no reader at all. The base implementation would also run on
physical state this class
+ // never initializes.
+ Status new_index_iterator(const std::shared_ptr<IndexFileReader>&
/*index_file_reader*/,
+ const TabletIndex* /*index_meta*/, const
std::string& /*rowset_id*/,
+ uint32_t /*segment_id*/, size_t
/*rows_of_segment*/,
+ std::unique_ptr<IndexIterator>* /*iterator*/)
override {
+ return Status::OK();
+ }
+
Review Comment:
[P1] Preserve constant semantics across cache eviction. The constant reader
is an ordinary LRU entry, so with capacity 1 and read order `[indexed c,
indexed commit TSO]`, column setup leaves the constant cached, then `c`'s bare
index lookup evicts it and the following TSO lookup rebuilds the physical
reader. This override is never reached; placeholder index 0 can eliminate real
TSO 42 for `tso > 20` while the retained row iterator yields 42. This is
distinct from the existing races because it is single-threaded and the correct
constant request already succeeded. Please derive the constant/no-index
decision from `StorageReadOptions` (or retain non-evictable semantic state) and
add a low-capacity end-to-end test.
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