arp7 commented on a change in pull request #798: HDDS-1499. OzoneManager Cache.
URL: https://github.com/apache/hadoop/pull/798#discussion_r285301711
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File path:
hadoop-hdds/common/src/main/java/org/apache/hadoop/utils/db/TypedTable.java
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@@ -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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