[GitHub] [geode] DonalEvans commented on a change in pull request #6701: GEODE-9429: Allow Radish HSCAN to handle all valid values for COUNT

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

DonalEvans commented on a change in pull request #6701:
URL: https://github.com/apache/geode/pull/6701#discussion_r671483756



##########
File path: geode-apis-compatible-with-redis/src/main/java/org/apache/geode/redis/internal/data/RedisHash.java
##########
@@ -237,35 +237,32 @@ public int hstrlen(byte[] field) {
     return new ArrayList<>(hash.keySet());
   }
 
-  public ImmutablePair<Integer, List<byte[]>> hscan(Pattern matchPattern,
-      int count,
-      int cursor) {
-
-    ArrayList<byte[]> resultList = new ArrayList<>(count + 2);
+  public ImmutablePair<Integer, List<ImmutablePair<byte[], byte[]>>> hscan(Pattern matchPattern,
+      int count, int cursor) {
+    // No need to allocate more space than it's possible to use given the size of the hash
+    int initialCapacity = Math.min(count, hash.size());
+    List<ImmutablePair<byte[], byte[]>> resultList = new ArrayList<>(initialCapacity);
     do {
       cursor = hash.scan(cursor, 1,
           (list, key, value) -> addIfMatching(matchPattern, list, key, value), resultList);
-    } while (cursor != 0 && resultList.size() < (count * 2));
+    } while (cursor != 0 && resultList.size() < count);
 
     return new ImmutablePair<>(cursor, resultList);
   }
 
-  private void addIfMatching(Pattern matchPattern, List<byte[]> resultList, byte[] key,
-      byte[] value) {
+  private void addIfMatching(Pattern matchPattern, List<ImmutablePair<byte[], byte[]>> resultList,
+      byte[] key, byte[] value) {
     if (matchPattern != null) {
       if (matchPattern.matcher(bytesToString(key)).matches()) {
-        resultList.add(key);
-        resultList.add(value);
+        resultList.add(new ImmutablePair<>(key, value));

Review comment:
       It's necessary to wrap the key and value in some object here, since the maximum length of a list returned by `HSCAN` is 2*(number of keys) which could in theory be greater than `Integer.MAX_VALUE`. If we want to assume that a user will never have that many keys in their Redish hash, then we can dispense with this pairing of values to increase efficiency and document that the maximum number of Redis hash keys we support is `Integer.MAX_VALUE / 2`, but if we want to be safe, then this is necessary.




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