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

[GitBox <gi...@apache.org>]

anuengineer commented on a change in pull request #1588: HDDS-1986. Fix listkeys API.
URL: https://github.com/apache/hadoop/pull/1588#discussion_r332256331
 
 

 ##########
 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()) {
 
 Review comment:
   I feel that we are better off leaving the old code in place...where we can read from the DB.. Worst, we might have to make sure that cache is flushed to DB before doing the list operation.But practically it may not matter.
   

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