HappenLee commented on code in PR #65482:
URL: https://github.com/apache/doris/pull/65482#discussion_r3578910527
##########
be/src/runtime/query_cache/query_cache.cpp:
##########
@@ -70,4 +97,267 @@ bool QueryCache::lookup(const CacheKey& key, int64_t
version, doris::QueryCacheH
return false;
}
+bool QueryCache::lookup_any_version(const CacheKey& key, QueryCacheHandle*
handle) {
+
SCOPED_SWITCH_THREAD_MEM_TRACKER_LIMITER(ExecEnv::GetInstance()->query_cache_mem_tracker());
+ auto* lru_handle = LRUCachePolicy::lookup(key);
+ if (lru_handle) {
+ *handle = QueryCacheHandle(this, lru_handle);
+ return true;
+ }
+ return false;
+}
+
+QueryCacheInstanceDecision::~QueryCacheInstanceDecision() = default;
+
+std::unique_ptr<TabletReadSource>
QueryCacheInstanceDecision::take_delta_read_source(
+ int64_t tablet_id) {
+ std::lock_guard<std::mutex> lock(_take_lock);
+ auto it = _delta_read_sources.find(tablet_id);
+ if (it == _delta_read_sources.end()) {
+ return nullptr;
+ }
+ auto res = std::move(it->second);
+ _delta_read_sources.erase(it);
+ return res;
+}
+
+std::shared_ptr<QueryCacheInstanceDecision>
QueryCacheRuntime::get_or_make_decision(
+ const std::vector<TScanRangeParams>& scan_ranges) {
+ std::string cache_key;
+ int64_t version = 0;
+ Status st = QueryCache::build_cache_key(scan_ranges, _param, &cache_key,
&version);
+ if (!st.ok()) {
+ // No reliable cache key for this instance (e.g. FE could not align the
+ // instance to a single partition so tablets carry different versions).
+ // Degrade to an uncached scan instead of failing the query: both the
+ // scan operator and the cache source operator observe the shared MISS
+ // decision with key_valid=false, so nothing is looked up and nothing
+ // is written back. This is an expected plan shape, so log only once
+ // per fragment instead of twice per instance.
+ std::lock_guard<std::mutex> lock(_lock);
+ if (_invalid_decision == nullptr) {
+ LOG(WARNING) << "query cache degrades to uncached scan, node_id="
<< _param.node_id
+ << ", reason: " << st.to_string();
+ _invalid_decision = std::make_shared<QueryCacheInstanceDecision>();
+ }
+ return _invalid_decision;
+ }
+
+ // The lock also serializes decision making of different instances of this
+ // fragment. That is acceptable in the common case: a decision only touches
+ // tablet metadata (no data IO), so it finishes in microseconds to
+ // milliseconds. On very wide fragments (hundreds of tablets per instance)
+ // combined with tablet header lock contention (e.g. compaction meta
+ // commits) this serialization can stretch the fragment init tail; if that
+ // ever shows up in profiles, move the capture out of the lock and let the
+ // losing racer drop its duplicate decision.
+ std::lock_guard<std::mutex> lock(_lock);
+ auto it = _decisions.find(cache_key);
+ if (it != _decisions.end()) {
+ return it->second;
+ }
+
+ auto decision = std::make_shared<QueryCacheInstanceDecision>();
+ decision->key_valid = true;
+ decision->cache_key = cache_key;
+ decision->current_version = version;
+ _make_decision(scan_ranges, decision.get());
+ _decisions.emplace(std::move(cache_key), decision);
+ return decision;
+}
+
+void QueryCacheRuntime::_make_decision(const std::vector<TScanRangeParams>&
scan_ranges,
+ QueryCacheInstanceDecision* decision) {
+ decision->mode = QueryCacheInstanceDecision::Mode::MISS;
+ if (_binlog_scan) {
+ // A row-binlog scan reads a different data stream under the same plan
+ // digest: it must neither serve cached blocks nor write its output
+ // back (that would poison the cache for normal queries).
+ decision->key_valid = false;
+ return;
+ }
+ if (_param.force_refresh_query_cache) {
+ return;
+ }
+
+ QueryCacheHandle handle;
+ if (!_cache->lookup_any_version(decision->cache_key, &handle)) {
+ return;
+ }
+ // Pin the entry: as long as this decision object lives, the entry cannot
be
+ // evicted, so every operator consuming this decision sees the same blocks.
+ decision->handle = std::move(handle);
+
+ if (decision->handle.get_cache_version() == decision->current_version) {
+ decision->mode = QueryCacheInstanceDecision::Mode::HIT;
+ decision->cached_delta_count =
decision->handle.get_cache_delta_count();
+ return;
+ }
+
+ if (_try_prepare_incremental(scan_ranges, decision)) {
+ decision->mode = QueryCacheInstanceDecision::Mode::INCREMENTAL;
+ DorisMetrics::instance()->query_cache_stale_hit_total->increment(1);
+ return;
+ }
+
+ // Stale entry not reusable: drop the pin and fall back to a full scan.
+ decision->_delta_read_sources.clear();
+ decision->handle = QueryCacheHandle();
+ decision->mode = QueryCacheInstanceDecision::Mode::MISS;
+ if (!decision->incremental_fallback_reason.empty()) {
+ // Only count real fallbacks: an empty reason means incremental merge
+ // was not enabled for this query in the first place.
+
DorisMetrics::instance()->query_cache_incremental_fallback_total->increment(1);
+ }
+}
+
+bool QueryCacheRuntime::_try_prepare_incremental(const
std::vector<TScanRangeParams>& scan_ranges,
+ QueryCacheInstanceDecision*
decision) {
+ if (!(_param.__isset.allow_incremental && _param.allow_incremental)) {
+ // Not a fallback: incremental merge is simply not enabled for this
+ // query, so leave incremental_fallback_reason empty.
+ return false;
+ }
+ // Cloud tablets capture rowsets through a different (partly asynchronous)
+ // path; incremental merge only supports local storage for now.
+ if (config::is_cloud_mode()) {
+ decision->incremental_fallback_reason = "cloud mode";
+ return false;
+ }
+
+ int64_t cached_version = decision->handle.get_cache_version();
+ if (cached_version >= decision->current_version) {
+ // The entry is newer than what this replica is asked to read (e.g. the
+ // entry was filled from another replica with a newer visible version).
+ // A full scan of the requested version is the only safe answer.
+ decision->incremental_fallback_reason = "cached entry is newer";
+ return false;
+ }
+ int64_t cached_delta_count = decision->handle.get_cache_delta_count();
+ if (cached_delta_count >= config::query_cache_max_incremental_merge_count)
{
+ // Force a full recompute to compact the entry: every incremental merge
+ // appends the delta blocks to the entry, so both the entry and the
+ // upstream merge get more fragmented as deltas accumulate.
+ decision->incremental_fallback_reason = "delta count reached
compaction threshold";
+ return false;
+ }
+
+ for (const auto& scan_range : scan_ranges) {
+ int64_t tablet_id = scan_range.scan_range.palo_scan_range.tablet_id;
+ if (!_capture_tablet_delta(tablet_id, cached_version, decision)) {
+ return false;
+ }
+ }
+
+ // If the cached entry alone already exceeds the entry limits, the merged
+ // entry (which can only be larger) could never be written back. Still scan
+ // only the delta, but tell the cache source upfront so it does not clone
+ // blocks for a write back that would be discarded anyway. Such an entry
+ // stays stale until compaction merges its delta away (then the capture
+ // above fails and a full recompute takes over).
+ if (decision->handle.get_cache_total_bytes() > _param.entry_max_bytes ||
Review Comment:
Under what circumstances would this condition be true? Is it possible that
the row count is set to 10 by the user during caching, and then set to 5 by the
user on the second run?
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