feat!: Improve file attribute caching (#854)

Add logging.

src/main/java/org/carlspring/cloud/storage/s3fs/cache/S3FileAttributesCache.java

@@ -2,12 +2,15 @@
 
 import com.github.benmanes.caffeine.cache.Cache;
 import com.github.benmanes.caffeine.cache.Caffeine;
+import com.github.benmanes.caffeine.cache.RemovalCause;
 import com.github.benmanes.caffeine.cache.stats.CacheStats;
 import org.carlspring.cloud.storage.s3fs.S3ObjectId;
 import org.carlspring.cloud.storage.s3fs.S3Path;
 import org.carlspring.cloud.storage.s3fs.attribute.S3BasicFileAttributes;
 import org.carlspring.cloud.storage.s3fs.attribute.S3PosixFileAttributes;
 import org.carlspring.cloud.storage.s3fs.util.S3Utils;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 import java.nio.file.NoSuchFileException;
 import java.nio.file.attribute.BasicFileAttributes;
@@ -20,6 +23,8 @@
 public class S3FileAttributesCache
 {
 
+    private static final Logger logger = LoggerFactory.getLogger(S3FileAttributesCache.class);
+
     private final S3Utils s3Utils = new S3Utils();
 
     // This should be volatile, despite what IntelliJ / Sonar says.
@@ -91,14 +96,18 @@ public static String generateCacheKey(S3ObjectId s3ObjectId, Class<? extends Bas
     public S3BasicFileAttributes get(final S3Path path, final Class<? extends BasicFileAttributes> attrType)
     {
         String key = generateCacheKey(path, attrType);
+        logger.trace("Get cache for key {}", key);
+
         Optional<S3BasicFileAttributes> attrs = cache.getIfPresent(key);
 
         // Don't get confused - Caffeine returns `null` if the key does not exist.
         if(attrs == null)
         {
+            logger.trace("No cache found for key {}", key);
             // We need a way to preserve non-existing files/paths.
             // This is necessary, because the Files.exist() method is called multiple times from different threads
             // during checks. As a result multiple requests for the same path are executed within milliseconds.
+            logger.trace("Fetch data for key {}", key);
             attrs = Optional.ofNullable(fetchAttribute(path, key));
             put(path, attrs);
         }
@@ -138,11 +147,13 @@ public void put(final S3Path path, final Optional<S3BasicFileAttributes> attrs)
         // To ensure this does not happen we always need to replace the BasicFileAttributes instances when
         // the PosixFileAttributes type is cached/updated.
         String basicKey = generateCacheKey(path, BasicFileAttributes.class);
+        logger.trace("Save response for key {}", basicKey);
         cache.put(basicKey, attrs);
 
         if(attrs.isPresent() && attrs.get() instanceof PosixFileAttributes)
         {
             String posixKey = generateCacheKey(path, PosixFileAttributes.class);
+            logger.trace("Save response for key {}", posixKey);
             cache.put(posixKey, attrs);
         }
     }
@@ -155,6 +166,7 @@ public void put(final S3Path path, final Optional<S3BasicFileAttributes> attrs)
     public void invalidate(final S3Path path, final Class<? extends BasicFileAttributes> attrType)
     {
         String key = generateCacheKey(path, attrType);
+        logger.trace("Invalidate cache key {}", key);
         cache.invalidate(key);
     }
 
@@ -211,6 +223,7 @@ public void invalidate(final S3ObjectId objectId)
         {
             try
             {
+                logger.trace("Invalidate cache key {}", key);
                 cache.invalidate(key);
             }
             catch (NullPointerException e)
@@ -224,6 +237,7 @@ public void invalidate(final S3ObjectId objectId)
 
     public void invalidateAll()
     {
+        logger.trace("Invalidate all cache");
         cache.invalidateAll();
     }
 
@@ -234,12 +248,17 @@ public CacheStats stats()
 
     protected Caffeine<String, Optional<S3BasicFileAttributes>> cacheBuilder(int cacheTTL, int cacheSize)
     {
-        return Caffeine.newBuilder()
-                       .expireAfter(new S3FileAttributesCachePolicy(cacheTTL))
-                       .maximumSize(cacheSize)
-                       .softValues()
-                       .recordStats()
-                ;
+        Caffeine<String, Optional<S3BasicFileAttributes>> builder = Caffeine.newBuilder()
+                                                                            .expireAfter(new S3FileAttributesCachePolicy(cacheTTL));
+
+        builder.maximumSize(cacheSize);
+        builder.recordStats();
+        builder.evictionListener((String key, Optional<S3BasicFileAttributes> value, RemovalCause cause) ->
+                logger.trace("Key {} was evicted (reason: {})", key, cause));
+        builder.removalListener((String key, Optional<S3BasicFileAttributes> value, RemovalCause cause) ->
+                logger.trace("Key {} was removed (reason: {})", key, cause));
+
+        return builder;
     }
 
     protected S3BasicFileAttributes fetchAttribute(S3Path path, String key)