github-actions[bot] commented on code in PR #68018:
URL: https://github.com/apache/doris/pull/68018#discussion_r4025665398
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be/src/storage/segment/column_reader_cache.cpp:
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@@ -60,6 +60,15 @@ std::shared_ptr<ColumnReader>
ColumnReaderCache::_lookup(const ColumnReaderCache
void ColumnReaderCache::_insert_locked_nocheck(const ColumnReaderCacheKey& key,
const
std::shared_ptr<ColumnReader>& reader) {
+ // Replacing an existing key updates its node in place. Pushing a second
node for the same key
+ // would leave the first one unreachable in the list while eviction erases
the map entry of
+ // whichever copy reaches the tail, dropping the live reader from the map.
+ if (auto it = _cache_map.find(key); it != _cache_map.end()) {
Review Comment:
[P1] Preserve the constant reader across concurrent misses. `_lookup`
releases `_cache_mutex` before construction, so a bare request can miss and
start building the physical reader, a constant request can then insert and
return its reader, and the first request reaches this branch last and
overwrites it. Since a cached `Segment` is shared, a query that already created
a `ConstantColumnIterator` can then do the bare index lookup and receive the
placeholder's physical index; for example, real commit TSO 42 with `tso > 20`
can be eliminated by an index containing 0, with the predicate removed from row
fallback. This is the inverse concurrent order from the existing sequential
comment. Please make the compare-and-upsert constant-dominant regardless of
arrival order, return the selected authoritative reader to the caller, and add
a barrier-controlled mixed physical/constant miss test.
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