Re: [PR] [CASSANDRA-21141][trunk] Reduce memory allocation during transformation of BatchStatement to Mutation [cassandra]

["clohfink (via GitHub)" <gi...@apache.org>]

clohfink commented on code in PR #4589:
URL: https://github.com/apache/cassandra/pull/4589#discussion_r2766638173


##########
src/java/org/apache/cassandra/cql3/restrictions/PartitionKeyRestrictions.java:
##########
@@ -191,6 +193,17 @@ public AbstractBounds<PartitionPosition> bounds(IPartitioner partitioner, QueryO
      */
     private List<ByteBuffer> nonTokenRestrictionValues(QueryOptions options, ClientState state)
     {
+        // fast path, a typical case when a single full restriction is used
+        // for example, when we specify a single partition key to modify
+        if (restrictions.size() == 1 && !restrictions.hasIN())
+        {
+            SingleRestriction r = restrictions.lastRestriction();
+            List<ClusteringElements> values = r.values(options);
+            if (values.size() == 1)
+                return toByteBuffers(Clustering.make(values.get(0).toArray(new ByteBuffer[comparator.size()])));

Review Comment:
   Minor additional possible improvement? For the single-column partition key case this is allocating:
     - 1 × ByteBuffer[] array (unnecessary)
     - 1 × BufferClustering object (unnecessary)
   
   to ultimately call get(0) and return the original ByteBuffer. Maybe bypass Clustering entirely and use ClusteringElements which has it
   
   
   ```          if (values.size() == 1)
             {
                 ClusteringElements elements = values.get(0);
                 ByteBuffer pk = serializePartitionKey(elements);
                 validatePartitionKey(pk);
                 return Collections.singletonList(pk);
             }
             return toByteBuffers(MultiCBuilder.build(comparator, values));
   
   ...
   
     private ByteBuffer serializePartitionKey(ClusteringElements elements)
     {
         // Single-column partition key: just return the value directly
         if (elements.size() == 1)
             return elements.get(0);
   
         // Composite partition key: need to build composite
         return CompositeType.build(ByteBufferAccessor.instance,
                                    elements.toArray(new ByteBuffer[elements.size()]));
     }
   
   ```
   
   



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