Merge pull request ClickHouse#79348 from ClickHouse/filesystem-cache-capacity

Add async metric about filesystem cache capacity

Author: alexey-milovidov

src/Interpreters/Cache/FileCache.cpp

@@ -1613,6 +1613,11 @@ size_t FileCache::getUsedCacheSize() const
     return main_priority->getSizeApprox();
 }
 
+size_t FileCache::getMaxCacheSize() const
+{
+    return main_priority->getSizeLimitApprox();
+}
+
 size_t FileCache::getFileSegmentsNum() const
 {
     /// We use this method for metrics, so it is ok to get approximate result.

src/Interpreters/Cache/FileCache.h

@@ -157,6 +157,7 @@ class FileCache : private boost::noncopyable
     std::vector<String> tryGetCachePaths(const Key & key);
 
     size_t getUsedCacheSize() const;
+    size_t getMaxCacheSize() const;
 
     size_t getFileSegmentsNum() const;
 

src/Interpreters/Cache/IFileCachePriority.h

@@ -97,6 +97,7 @@ class IFileCachePriority : private boost::noncopyable
     size_t getElementsLimit(const CachePriorityGuard::Lock &) const { return max_elements; }
 
     size_t getSizeLimit(const CachePriorityGuard::Lock &) const { return max_size; }
+    size_t getSizeLimitApprox() const { return max_size.load(std::memory_order_relaxed); }
 
     virtual size_t getSize(const CachePriorityGuard::Lock &) const = 0;
 

src/Interpreters/ServerAsynchronousMetrics.cpp

@@ -144,16 +144,20 @@ void ServerAsynchronousMetrics::updateImpl(TimePoint update_time, TimePoint curr
     {
         auto caches = FileCacheFactory::instance().getAll();
         size_t total_bytes = 0;
+        size_t max_bytes = 0;
         size_t total_files = 0;
 
         for (const auto & [_, cache_data] : caches)
         {
             total_bytes += cache_data->cache->getUsedCacheSize();
+            max_bytes += cache_data->cache->getMaxCacheSize();
             total_files += cache_data->cache->getFileSegmentsNum();
         }
 
         new_values["FilesystemCacheBytes"] = { total_bytes,
             "Total bytes in the `cache` virtual filesystem. This cache is hold on disk." };
+        new_values["FilesystemCacheCapacity"] = { max_bytes,
+            "Total capacity in the `cache` virtual filesystem. This cache is hold on disk." };
         new_values["FilesystemCacheFiles"] = { total_files,
             "Total number of cached file segments in the `cache` virtual filesystem. This cache is hold on disk." };
     }