[GitHub] [hadoop] nandakumar131 commented on a change in pull request #1588: HDDS-1986. Fix listkeys API.

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nandakumar131 commented on a change in pull request #1588: HDDS-1986. Fix listkeys API.
URL: https://github.com/apache/hadoop/pull/1588#discussion_r333692284
 
 

 ##########
 File path: hadoop-ozone/ozone-manager/src/main/java/org/apache/hadoop/ozone/om/OmMetadataManagerImpl.java
 ##########
 @@ -680,26 +688,85 @@ public boolean isBucketEmpty(String volume, String bucket)
       seekPrefix = getBucketKey(volumeName, bucketName + OM_KEY_PREFIX);
     }
     int currentCount = 0;
-    try (TableIterator<String, ? extends KeyValue<String, OmKeyInfo>> keyIter =
-        getKeyTable()
-            .iterator()) {
-      KeyValue<String, OmKeyInfo> kv = keyIter.seek(seekKey);
-      while (currentCount < maxKeys && keyIter.hasNext()) {
-        kv = keyIter.next();
-        // Skip the Start key if needed.
-        if (kv != null && skipStartKey && kv.getKey().equals(seekKey)) {
-          continue;
+
+
+    TreeMap<String, OmKeyInfo> cacheKeyMap = new TreeMap<>();
+    Set<String> deletedKeySet = new TreeSet<>();
+    Iterator<Map.Entry<CacheKey<String>, CacheValue<OmKeyInfo>>> iterator =
+        keyTable.cacheIterator();
+
+    //TODO: We can avoid this iteration if table cache has stored entries in
+    // treemap. Currently HashMap is used in Cache. HashMap get operation is an
+    // constant time operation, where as for treeMap get is log(n).
+    // So if we move to treemap, the get operation will be affected. As get
+    // is frequent operation on table. So, for now in list we iterate cache map
+    // and construct treeMap which match with keyPrefix and are greater than or
+    // equal to startKey. Later we can revisit this, if list operation
+    // is becoming slow.
+    while (iterator.hasNext()) {
+      Map.Entry< CacheKey<String>, CacheValue<OmKeyInfo>> entry =
+          iterator.next();
+
+      String key = entry.getKey().getCacheKey();
+      OmKeyInfo omKeyInfo = entry.getValue().getCacheValue();
+      // Making sure that entry in cache is not for delete key request.
+
+      if (omKeyInfo != null) {
+        if (key.startsWith(seekPrefix) && key.compareTo(seekKey) >= 0) {
 
 Review comment:
   If there is a key which matches exactly with the `keyPrefix` that is passed to the list call and the `startKey` value is null/empty, we have to include that in the result.
   If that particular key happens to be in the Cache, we are ignoring it.
   `key.compareTo(seekKey) >= 0` --> will evaluate to false

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