[GitHub] [cassandra] jonmeredith commented on a diff in pull request #1723: CASSANDRA-17240: Trie memtable

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

jonmeredith commented on code in PR #1723:
URL: https://github.com/apache/cassandra/pull/1723#discussion_r994052887


##########
src/java/org/apache/cassandra/db/tries/MemtableTrie.java:
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@@ -0,0 +1,1039 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.cassandra.db.tries;
+
+import java.nio.ByteBuffer;
+import java.util.Arrays;
+import java.util.Iterator;
+import java.util.NoSuchElementException;
+import java.util.concurrent.atomic.AtomicReferenceArray;
+
+import com.google.common.annotations.VisibleForTesting;
+
+import org.agrona.concurrent.UnsafeBuffer;
+import org.apache.cassandra.io.compress.BufferType;
+import org.apache.cassandra.io.util.FileUtils;
+import org.apache.cassandra.utils.bytecomparable.ByteSource;
+import org.apache.cassandra.utils.bytecomparable.ByteComparable;
+import org.apache.cassandra.utils.ObjectSizes;
+import org.github.jamm.MemoryLayoutSpecification;
+
+/**
+ * Memtable trie, i.e. an in-memory trie built for fast modification and reads executing concurrently with writes from
+ * a single mutator thread.
+ *
+ * Writes to this should be atomic (i.e. reads should see either the content before the write, or the content after the
+ * write; if any read sees the write, then any subsequent (i.e. started after it completed) read should also see it).
+ * This implementation does not currently guarantee this, but we still get the desired result as `apply` is only used
+ * with singleton tries.
+ */
+public class MemtableTrie<T> extends MemtableReadTrie<T>
+{
+    // See the trie format description in MemtableReadTrie.
+
+    /**
+     * Trie size limit. This is not enforced, but users must check from time to time that it is not exceeded (using
+     * reachedAllocatedSizeThreshold()) and start switching to a new trie if it is.
+     * This must be done to avoid tries growing beyond their hard 2GB size limit (due to the 32-bit pointers).
+     */
+    private static final int ALLOCATED_SIZE_THRESHOLD;
+    static
+    {
+        String propertyName = "dse.trie_size_limit_mb";

Review Comment:
   Should this move to `CassandraRelevantProperties` and have the prefix changed from `dse.` to `cassandra.`?



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