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From GitBox <...@apache.org>
Subject [GitHub] [hadoop] arp7 commented on a change in pull request #798: HDDS-1499. OzoneManager Cache.
Date Fri, 17 May 2019 22:05:26 GMT
arp7 commented on a change in pull request #798: HDDS-1499. OzoneManager Cache.
URL: https://github.com/apache/hadoop/pull/798#discussion_r285301711
 
 

 ##########
 File path: hadoop-hdds/common/src/main/java/org/apache/hadoop/utils/db/TypedTable.java
 ##########
 @@ -69,8 +79,34 @@ public boolean isEmpty() throws IOException {
     return rawTable.isEmpty();
   }
 
+  /**
+   * Returns the value mapped to the given key in byte array or returns null
+   * if the key is not found.
+   *
+   * Caller's of this method should use synchronization mechanism, when
+   * accessing. First it will check from cache, if it has entry return the
+   * value, otherwise get from the RocksDB table.
+   *
+   * @param key metadata key
+   * @return VALUE
+   * @throws IOException
+   */
   @Override
   public VALUE get(KEY key) throws IOException {
+    // Here the metadata lock will guarantee that cache is not updated for same
+    // key during get key.
+    CacheValue< VALUE > cacheValue = cache.get(new CacheKey<>(key));
+    if (cacheValue == null) {
+      // If no cache for the table or if it does not exist in cache get from
+      // RocksDB table.
+      return getFromTable(key);
+    } else {
+      // We have a value in cache, return the value.
+      return cacheValue.getValue();
 
 Review comment:
   cacheValue.getValue() can be a null to indicate deletion, correct?

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