[GitHub] [hadoop] arp7 commented on a change in pull request #1588: HDDS-1986. Fix listkeys API.

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

arp7 commented on a change in pull request #1588: HDDS-1986. Fix listkeys API.
URL: https://github.com/apache/hadoop/pull/1588#discussion_r332303770
 
 

 ##########
 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) {
+          cacheKeyMap.put(key, omKeyInfo);
         }
+      } else {
+        deletedKeySet.add(key);
+      }
+    }
+
+    // Get maxKeys from DB if it has.
+
+    try (TableIterator<String, ? extends KeyValue<String, OmKeyInfo>>
+             keyIter = getKeyTable().iterator()) {
+      KeyValue< String, OmKeyInfo > kv;
+      keyIter.seek(seekKey);
+      // we need to iterate maxKeys + 1 here because if skipStartKey is true,
+      // we should skip that entry and return the result.
+      while (currentCount < maxKeys + 1 && keyIter.hasNext()) {
+        kv = keyIter.next();
         if (kv != null && kv.getKey().startsWith(seekPrefix)) {
-          result.add(kv.getValue());
-          currentCount++;
+
+          // Entry should not be marked for delete, consider only those
+          // entries.
+          if(!deletedKeySet.contains(kv.getKey())) {
+            cacheKeyMap.put(kv.getKey(), kv.getValue());
+            currentCount++;
+          }
         } else {
           // The SeekPrefix does not match any more, we can break out of the
           // loop.
           break;
         }
       }
     }
+
+    // Finally DB entries and cache entries are merged, then return the count
+    // of maxKeys from the sorted map.
+    currentCount = 0;
+
+    for (Map.Entry<String, OmKeyInfo>  cacheKey : cacheKeyMap.entrySet()) {
 
 Review comment:
   The second iteration is unfortunate. We should see if there is a way to avoid it.

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