[GitHub] ivankelly commented on a change in pull request #828: DbLedgerStorage -- Write cache

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

ivankelly commented on a change in pull request #828: DbLedgerStorage -- Write cache
URL: https://github.com/apache/bookkeeper/pull/828#discussion_r156182239
 
 

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 File path: bookkeeper-server/src/main/java/org/apache/bookkeeper/bookie/storage/ldb/WriteCache.java
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+/**
+ *
+ * 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 io.netty.buffer.ByteBuf;
+import io.netty.buffer.ByteBufAllocator;
+import io.netty.buffer.Unpooled;
+
+import java.io.Closeable;
+import java.util.concurrent.atomic.AtomicLong;
+import java.util.concurrent.atomic.LongAdder;
+import java.util.concurrent.locks.ReentrantLock;
+
+import org.apache.bookkeeper.util.collections.ConcurrentLongHashSet;
+import org.apache.bookkeeper.util.collections.ConcurrentLongLongHashMap;
+import org.apache.bookkeeper.util.collections.ConcurrentLongLongPairHashMap;
+import org.apache.bookkeeper.util.collections.ConcurrentLongLongPairHashMap.LongPair;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Write cache implementation.
+ *
+ * <p>The write cache will allocate the requested size from direct memory
+ * and it will break it down into multiple segments.
+ *
+ * <p>The entries are appended in a common buffer and indexed though a
+ * hashmap, until the cache is cleared.
+ *
+ * <p>There is the possibility to iterate through the stored entries in
+ * an ordered way, by (ledgerId, entry).
+ */
+public class WriteCache implements Closeable {
+
+    /**
+     * Consumer that is used to scan the entire write cache.
+     */
+    public interface EntryConsumer {
+        void accept(long ledgerId, long entryId, ByteBuf entry);
+    }
+
+    private final ConcurrentLongLongPairHashMap index = new ConcurrentLongLongPairHashMap(4096,
 
 Review comment:
   nit: Break these lines before the new

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