[GitHub] merlimat commented on a change in pull request #843: DbLedgerStorage -- ReadCache

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merlimat commented on a change in pull request #843: DbLedgerStorage -- ReadCache
URL: https://github.com/apache/bookkeeper/pull/843#discussion_r156818822
 
 

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 File path: bookkeeper-server/src/main/java/org/apache/bookkeeper/bookie/storage/ldb/ReadCache.java
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 @@ -0,0 +1,197 @@
+/**
+ *
+ * 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.bookkeeper.bookie.storage.ldb;
+
+import static org.apache.bookkeeper.bookie.storage.ldb.WriteCache.align64;
+
+import io.netty.buffer.ByteBuf;
+import io.netty.buffer.ByteBufAllocator;
+import io.netty.buffer.Unpooled;
+
+import java.io.Closeable;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.locks.ReentrantReadWriteLock;
+
+import org.apache.bookkeeper.util.collections.ConcurrentLongLongPairHashMap;
+import org.apache.bookkeeper.util.collections.ConcurrentLongLongPairHashMap.LongPair;
+
+/**
+ * Read cache implementation.
+ *
+ * <p>Uses the specified amount of memory and pairs it with a hashmap.
+ *
+ * <p>The memory is splitted in multiple segments that are used in a
+ * ring-buffer fashion. When the read cache is full, the oldest segment
+ * is cleared and rotated to make space for new entries to be added to
+ * the read cache.
+ */
+public class ReadCache implements Closeable {
+
+    private static final int DEFAULT_MAX_SEGMENT_SIZE = 1 * 1024 * 1024 * 1024;
+
+    private final List<ByteBuf> cacheSegments;
+    private final List<ConcurrentLongLongPairHashMap> cacheIndexes;
+
+    private int currentSegmentIdx;
+    private AtomicInteger currentSegmentOffset = new AtomicInteger(0);
 
 Review comment:
   yes, I thought it was being reassigned but it's not. 

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