Better

src/Interpreters/Cache/EvictionCandidates.h

@@ -10,15 +10,6 @@ public:
     using FinalizeEvictionFunc = std::function<void(const CachePriorityGuard::Lock & lk)>;
 
     EvictionCandidates() = default;
-    EvictionCandidates(EvictionCandidates && other) noexcept
-    {
-        candidates = std::move(other.candidates);
-        candidates_size = std::move(other.candidates_size);
-        on_finalize = std::move(other.on_finalize);
-        queue_entries_to_invalidate = std::move(other.queue_entries_to_invalidate);
-        hold_space = std::move(other.hold_space);
-    }
-
     ~EvictionCandidates();
 
     void add(
@@ -26,8 +17,6 @@ public:
         LockedKey & locked_key,
         const CachePriorityGuard::Lock &);
 
-    void add(const EvictionCandidates & other, const CachePriorityGuard::Lock &) { candidates.insert(other.candidates.begin(), other.candidates.end()); }
-
     void evict();
 
     void onFinalize(FinalizeEvictionFunc && func) { on_finalize.emplace_back(std::move(func)); }

src/Interpreters/Cache/FileCache.cpp

@@ -953,12 +953,15 @@ void FileCache::freeSpaceRatioKeepingThreadFunc()
     static constexpr auto space_ratio_satisfied_reschedule_ms = 5000;
     static constexpr auto general_reschedule_ms = 5000;
 
-    while (true)
-    {
     if (shutdown)
         return;
 
+    Stopwatch watch;
+
     auto lock = tryLockCache();
+
+    /// To avoid deteriorating contention on cache,
+    /// proceed only if cache is not heavily used.
     if (!lock)
     {
         keep_up_free_space_ratio_task->scheduleAfter(lock_failed_reschedule_ms);
@@ -979,23 +982,42 @@ void FileCache::freeSpaceRatioKeepingThreadFunc()
         return;
     }
 
+    FileCacheReserveStat stat;
+    EvictionCandidates eviction_candidates;
+
     try
     {
-            FileCacheReserveStat stat;
+        /// Collect at most `keep_up_free_space_remove_batch` elements to evict,
-            auto eviction_candidates = main_priority->collectCandidatesForEviction(
+        /// (we use batches to make sure we do not block cache for too long,
-                desired_size, desired_elements_num, keep_up_free_space_remove_batch, stat, lock);
+        /// by default the batch size is quite small).
+        const bool limits_satisfied = main_priority->collectCandidatesForEviction(
+            desired_size, desired_elements_num, keep_up_free_space_remove_batch, stat, eviction_candidates, lock);
+
+#ifdef ABORT_ON_LOGICAL_ERROR
+        /// Let's make sure that we correctly processed the limits.
+        if (limits_satisfied && eviction_candidates.size() < keep_up_free_space_remove_batch)
+        {
+            const auto current_size = main_priority->getSize(lock);
+            chassert(current_size >= stat.total_stat.releasable_size);
+            chassert(!size_limit
+                        || current_size <= desired_size
+                        || current_size - stat.total_stat.releasable_size <= desired_size);
+
+            const auto current_elements_count = main_priority->getElementsCount(lock);
+            chassert(current_elements_count >= stat.total_stat.releasable_count);
+            chassert(!elements_limit
+                        || current_elements_count <= desired_elements_num
+                        || current_elements_count - stat.total_stat.releasable_count <= desired_elements_num);
+        }
+#else
+        UNUSED(limits_satisfied);
+#endif
 
         if (shutdown)
             return;
 
-            if (eviction_candidates.size() == 0)
+        if (eviction_candidates.size() > 0)
         {
-                /// This case is impossible in realistic cache setup,
-                /// e.g. we should always be able to evict something.
-                keep_up_free_space_ratio_task->scheduleAfter(general_reschedule_ms);
-                return;
-            }
-
             LOG_TRACE(log, "Current usage {}/{} in size, {}/{} in elements count "
                     "(trying to keep size ration at {} and elements ratio at {}). "
                     "Collected {} eviction candidates, "
@@ -1006,20 +1028,35 @@ void FileCache::freeSpaceRatioKeepingThreadFunc()
                     eviction_candidates.size(), stat.total_stat.non_releasable_count);
 
             lock.unlock();
+
+            /// Remove files from filesystem.
             eviction_candidates.evict();
 
+            /// Take lock again to finalize eviction,
+            /// e.g. to update the in-memory state.
             lock.lock();
             eviction_candidates.finalize(nullptr, lock);
         }
+        else
+        {
+            keep_up_free_space_ratio_task->scheduleAfter(general_reschedule_ms);
+        }
+    }
     catch (...)
     {
         tryLogCurrentException(__PRETTY_FUNCTION__);
+
+        if (eviction_candidates.size() > 0)
+            eviction_candidates.finalize(nullptr, lockCache());
+
         keep_up_free_space_ratio_task->scheduleAfter(general_reschedule_ms);
 
-            /// Let's catch such cases in ci, in general there should not be exceptions.
+        /// Let's catch such cases in ci,
+        /// in general there should not be exceptions.
         chassert(false);
     }
-    }
+
+    LOG_TRACE(log, "Free space ratio keeping thread finished in {} ms", watch.elapsedMilliseconds());
 }
 
 void FileCache::iterate(IterateFunc && func, const UserID & user_id)

src/Interpreters/Cache/IFileCachePriority.h

@@ -148,11 +148,12 @@ public:
         const CachePriorityGuard::Lock &) = 0;
 
     /// Collect eviction `candidates_num` candidates for eviction.
-    virtual EvictionCandidates collectCandidatesForEviction(
+    virtual bool collectCandidatesForEviction(
         size_t desired_size,
         size_t desired_elements_count,
         size_t max_candidates_to_evict,
         FileCacheReserveStat & stat,
+        EvictionCandidates & candidates,
         const CachePriorityGuard::Lock &) = 0;
 
     virtual bool modifySizeLimits(size_t max_size_, size_t max_elements_, double size_ratio_, const CachePriorityGuard::Lock &) = 0;

src/Interpreters/Cache/LRUFileCachePriority.cpp

@@ -322,24 +322,24 @@ bool LRUFileCachePriority::collectCandidatesForEviction(
     }
 }
 
-EvictionCandidates LRUFileCachePriority::collectCandidatesForEviction(
+bool LRUFileCachePriority::collectCandidatesForEviction(
     size_t desired_size,
     size_t desired_elements_count,
     size_t max_candidates_to_evict,
     FileCacheReserveStat & stat,
+    EvictionCandidates & res,
     const CachePriorityGuard::Lock & lock)
 {
     if (!max_candidates_to_evict)
         return {};
 
-    EvictionCandidates res;
     auto stop_condition = [&, this]()
     {
         return (getSize(lock) <= desired_size && getElementsCount(lock) <= desired_elements_count)
             || res.size() >= max_candidates_to_evict;
     };
     iterateForEviction(res, stat, stop_condition, lock);
-    return res;
+    return stop_condition();
 }
 
 void LRUFileCachePriority::iterateForEviction(

src/Interpreters/Cache/LRUFileCachePriority.h

@@ -62,11 +62,12 @@ public:
         const UserID & user_id,
         const CachePriorityGuard::Lock &) override;
 
-    EvictionCandidates collectCandidatesForEviction(
+    bool collectCandidatesForEviction(
         size_t desired_size,
         size_t desired_elements_count,
         size_t max_candidates_to_evict,
         FileCacheReserveStat & stat,
+        EvictionCandidates & res,
         const CachePriorityGuard::Lock &) override;
 
     void shuffle(const CachePriorityGuard::Lock &) override;

src/Interpreters/Cache/SLRUFileCachePriority.cpp

@@ -251,11 +251,12 @@ bool SLRUFileCachePriority::collectCandidatesForEvictionInProtected(
     return true;
 }
 
-EvictionCandidates SLRUFileCachePriority::collectCandidatesForEviction(
+bool SLRUFileCachePriority::collectCandidatesForEviction(
     size_t desired_size,
     size_t desired_elements_count,
     size_t max_candidates_to_evict,
     FileCacheReserveStat & stat,
+    EvictionCandidates & res,
     const CachePriorityGuard::Lock & lock)
 {
     if (!max_candidates_to_evict)
@@ -264,22 +265,36 @@ EvictionCandidates SLRUFileCachePriority::collectCandidatesForEviction(
     const auto desired_probationary_size = getRatio(desired_size, 1 - size_ratio);
     const auto desired_probationary_elements_num = getRatio(desired_elements_count, 1 - size_ratio);
 
-    auto res = probationary_queue.collectCandidatesForEviction(
+    FileCacheReserveStat probationary_stat;
-        desired_probationary_size, desired_probationary_elements_num, max_candidates_to_evict, stat, lock);
+    const bool probationary_limit_satisfied = probationary_queue.collectCandidatesForEviction(
+        desired_probationary_size, desired_probationary_elements_num,
+        max_candidates_to_evict, probationary_stat, res, lock);
+
+    stat += probationary_stat;
+
+    LOG_TEST(log, "Collected {} to evict from probationary queue. Total size: {}",
+             res.size(), probationary_stat.total_stat.releasable_size);
 
     chassert(res.size() <= max_candidates_to_evict);
     chassert(res.size() == stat.total_stat.releasable_count);
 
-    if (res.size() == max_candidates_to_evict)
+    if (res.size() >= max_candidates_to_evict)
-        return res;
+        return probationary_limit_satisfied;
 
     const auto desired_protected_size = getRatio(max_size, size_ratio);
     const auto desired_protected_elements_num = getRatio(max_elements, size_ratio);
 
-    auto res_add = protected_queue.collectCandidatesForEviction(
+    FileCacheReserveStat protected_stat;
-        desired_protected_size, desired_protected_elements_num, max_candidates_to_evict - res.size(), stat, lock);
+    const bool protected_limit_satisfied = protected_queue.collectCandidatesForEviction(
-    res.add(res_add, lock);
+        desired_protected_size, desired_protected_elements_num,
-    return res;
+        max_candidates_to_evict - res.size(), protected_stat, res, lock);
+
+    stat += protected_stat;
+
+    LOG_TEST(log, "Collected {} to evict from protected queue. Total size: {}",
+             res.size(), protected_stat.total_stat.releasable_size);
+
+    return probationary_limit_satisfied && protected_limit_satisfied;
 }
 
 void SLRUFileCachePriority::downgrade(IteratorPtr iterator, const CachePriorityGuard::Lock & lock)

src/Interpreters/Cache/SLRUFileCachePriority.h

@@ -58,11 +58,12 @@ public:
         const UserID & user_id,
         const CachePriorityGuard::Lock &) override;
 
-    EvictionCandidates collectCandidatesForEviction(
+    bool collectCandidatesForEviction(
         size_t desired_size,
         size_t desired_elements_count,
         size_t max_candidates_to_evict,
         FileCacheReserveStat & stat,
+        EvictionCandidates & res,
         const CachePriorityGuard::Lock &) override;
 
     void shuffle(const CachePriorityGuard::Lock &) override;

tests/config/config.d/storage_conf.xml

@@ -19,13 +19,13 @@
                 <type>cache</type>
                 <disk>s3_disk</disk>
                 <path>s3_cache/</path>
-                <max_size>64Mi</max_size>
+                <max_size>100Mi</max_size>
                 <cache_on_write_operations>1</cache_on_write_operations>
                 <delayed_cleanup_interval_ms>100</delayed_cleanup_interval_ms>
                 <cache_policy>LRU</cache_policy>
                 <slru_size_ratio>0.3</slru_size_ratio>
-                <keep_free_space_size_ratio>0.1</keep_free_space_size_ratio>
+                <keep_free_space_size_ratio>0.15</keep_free_space_size_ratio>
-                <keep_free_space_elements_ratio>0.1</keep_free_space_elements_ratio>
+                <keep_free_space_elements_ratio>0.15</keep_free_space_elements_ratio>
             </s3_cache>
             <s3_cache_02933>
                 <type>cache</type>