[GitHub] [incubator-iotdb] LeiRui commented on a change in pull request #262: [IOTDB-144]meta data cache for query

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LeiRui commented on a change in pull request #262: [IOTDB-144]meta data cache for query
URL: https://github.com/apache/incubator-iotdb/pull/262#discussion_r305598959
 
 

 ##########
 File path: iotdb/src/main/java/org/apache/iotdb/db/engine/cache/DeviceMetaDataCache.java
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 @@ -19,77 +19,144 @@
 package org.apache.iotdb.db.engine.cache;
 
 import java.io.IOException;
-import java.util.LinkedHashMap;
+import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.List;
 import java.util.Map;
-import java.util.Objects;
+import java.util.Set;
 import java.util.concurrent.atomic.AtomicLong;
+import org.apache.iotdb.db.conf.IoTDBConfig;
+import org.apache.iotdb.db.conf.IoTDBDescriptor;
+import org.apache.iotdb.db.engine.StorageEngine;
+import org.apache.iotdb.tsfile.file.metadata.ChunkMetaData;
 import org.apache.iotdb.tsfile.file.metadata.TsDeviceMetadata;
 import org.apache.iotdb.tsfile.file.metadata.TsFileMetaData;
+import org.apache.iotdb.tsfile.read.common.Path;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
 /**
- * This class is used to cache <code>DeviceMetaDataCache</code> of tsfile in IoTDB.
+ * This class is used to cache <code>List<ChunkMetaData></code> of tsfile in IoTDB. The caching
+ * strategy is LRU.
  */
 public class DeviceMetaDataCache {
 
   private static final Logger logger = LoggerFactory.getLogger(DeviceMetaDataCache.class);
+  private static final IoTDBConfig config = IoTDBDescriptor.getInstance().getConfig();
 
-  private static final int CACHE_SIZE = 100;
+  private static StorageEngine storageEngine = StorageEngine.getInstance();
+
+  private static final long MEMORY_THRESHOLD_IN_B = (long) (0.3 * config
+      .getAllocateMemoryForRead());
   /**
-   * key: the file path + deviceId.
+   * key: file path dot deviceId dot sensorId.
+   * <p>
+   * value: chunkMetaData list of one timeseries in the file.
    */
-  private LinkedHashMap<String, TsDeviceMetadata> lruCache;
+  private LruLinkedHashMap<String, List<ChunkMetaData>> lruCache;
 
   private AtomicLong cacheHintNum = new AtomicLong();
   private AtomicLong cacheRequestNum = new AtomicLong();
 
-  private DeviceMetaDataCache(int cacheSize) {
-    lruCache = new LruLinkedHashMap(cacheSize, true);
+  /**
+   * approximate estimation of chunkMetaData size
+   */
+  private long chunkMetaDataSize = 0;
+
+  private DeviceMetaDataCache(long memoryThreshold) {
+    lruCache = new LruLinkedHashMap<String, List<ChunkMetaData>>(memoryThreshold, true) {
+      @Override
+      protected long calEntrySize(String key, List<ChunkMetaData> value) {
+        if (chunkMetaDataSize == 0 && !value.isEmpty()) {
+          chunkMetaDataSize = RamUsageEstimator.sizeOf(value.get(0));
+        }
+        return value.size() * chunkMetaDataSize + key.length() * 2;
 
 Review comment:
   Why `+key.length() * 2` here? 
   It is `ChunkMetaData` not `TsFileMetaData`.

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