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https://issues.apache.org/jira/browse/GEODE-8864?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17285906#comment-17285906
 ] 

ASF GitHub Bot commented on GEODE-8864:
---------------------------------------

jhutchison commented on a change in pull request #5954:
URL: https://github.com/apache/geode/pull/5954#discussion_r577727315



##########
File path: 
geode-redis/src/main/java/org/apache/geode/redis/internal/data/RedisHash.java
##########
@@ -203,49 +261,120 @@ public int hstrlen(ByteArrayWrapper field) {
     return new ArrayList<>(hash.keySet());
   }
 
-  public Pair<BigInteger, List<Object>> hscan(Pattern matchPattern, int count, 
BigInteger cursor) {
-    List<Object> returnList = new ArrayList<Object>();
-    int size = hash.size();
-    BigInteger beforeCursor = new BigInteger("0");
-    int numElements = 0;
-    int i = -1;
-    for (Map.Entry<ByteArrayWrapper, ByteArrayWrapper> entry : 
hash.entrySet()) {
-      ByteArrayWrapper key = entry.getKey();
-      ByteArrayWrapper value = entry.getValue();
-      i++;
-      if (beforeCursor.compareTo(cursor) < 0) {
-        beforeCursor = beforeCursor.add(new BigInteger("1"));
+  public Pair<BigInteger, List<Object>> hscan(UUID clientID, Pattern 
matchPattern,
+      int count,
+      BigInteger cursorParameter) {
+
+    int startCursor = cursorParameter.intValue();
+
+    List<ByteArrayWrapper> keysToScan = getSnapShotOfKeySet(clientID);
+
+    List<Object> resultList =
+        getResultList(keysToScan, startCursor, count, matchPattern);
+
+    int indexOfLast = resultList.size() - 1;
+    int numberOfIterationsCompleted = 
Integer.parseInt(resultList.get(indexOfLast).toString());
+    resultList.remove(indexOfLast);
+
+    int returnCursorValueAsInt =
+        getCursorValueToReturn(startCursor, numberOfIterationsCompleted, 
keysToScan);
+
+    if (returnCursorValueAsInt == 0) {
+      removeHSCANSnapshot(clientID);
+    }
+    return new ImmutablePair<>(BigInteger.valueOf(returnCursorValueAsInt), 
resultList);
+  }
+
+  private void removeHSCANSnapshot(UUID clientID) {
+    this.hScanSnapShots.remove(clientID);
+    this.hScanSnapShotCreationTimes.remove(clientID);
+
+    if (this.hScanSnapShots.isEmpty()) {
+      shutDownHscanSnapshotScheduledRemoval();
+    }
+  }
+
+  private List<Object> getResultList(List<ByteArrayWrapper> keysSnapShot,
+      int startCursor,
+      int count,
+      Pattern matchPattern) {
+
+    int indexOfKeys = 0;
+
+    List<Object> resultList = new ArrayList<>();
+
+    for (ByteArrayWrapper key : keysSnapShot) {
+
+      if (indexOfKeys < startCursor) {
+        indexOfKeys++;
+        continue;
+      }
+
+      indexOfKeys++;
+
+      ByteArrayWrapper value = hash.get(key);
+      if (value == null) {
         continue;
       }
 
       if (matchPattern != null) {
         if (matchPattern.matcher(key.toString()).matches()) {
-          returnList.add(key);
-          returnList.add(value);
-          numElements++;
+          resultList.add(key);
+          resultList.add(value);
         }
       } else {
-        returnList.add(key);
-        returnList.add(value);
-        numElements++;
+        resultList.add(key);
+        resultList.add(value);
       }
 
-      if (numElements == count) {
+      if ((indexOfKeys - startCursor) == count) {

Review comment:
       As per Redis docs, the match is applied after the count of elements are 
received.  So if Matching parameter is passed in, then resultSize might not be 
what we want, if we are mirroring native Redis.  We could do it 
differently...not sure if we need to mirror redis here?   




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> finish implementation of Redis HScan Command
> --------------------------------------------
>
>                 Key: GEODE-8864
>                 URL: https://issues.apache.org/jira/browse/GEODE-8864
>             Project: Geode
>          Issue Type: New Feature
>          Components: redis
>            Reporter: John Hutchison
>            Priority: Major
>              Labels: pull-request-available
>




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