HBASE-21879 Read HFile ’s Block into ByteBuffer directly. 1. Background For reducing the Java GC impact to p99/p999 RPC latency, HBase 2.x has made an offheap read and write path. The KV are allocated didn’t accomplish this before because HDFS does not support the ByteBuffer pread interface, also because of its complexity. For the ByteBuffer pread, we have issue ​HDFS-3246​ to track this, so further HDFS can also be easy as the 3.1 part described. 3.3 Make downstream API can accept ByteBuff or ByteBuffer as arguments The first obstacle when implementing the block off-heap reading is: many downstream

nel fileChannel = AsynchronousFileChannel.open(path, StandardOpenOption.READ); ByteBuffer buffer = ByteBuffer.allocate(1024); long position = 0; Future operation = fileChannel.read(buffer CompletionHandlerByteBuffer>() { //Once the read operation finishes the CompletionHandler's completed() method will be calle . @Override public void completed(Integer result, ByteBuffer attachment) CompletionHandler will get called inst ad. @Override public void failed(Throwable exc, ByteBuffer attachment) { } }); 3. Writing Data ● Writing Data Via a Future Path path = Paths.get("data/test-write

Integer.MAX_VALUE; } 如果启用 transientStorePoolEnable 机制，返回当前可用的 ByteBuffer 个数，即整 个 isTransientStorePoolDeficient 方法的用意是是否还存在可用的 ByteBuffer，如果不 存在，即表示 pageCache 繁忙。那什么是 transientStorePoolEnable 机制呢？ 3 MappedFile 的 ByteBuffer writeBuffer、MappedByteBuffer mapped ByteBuffer 这两个属性的初始化，因为这两个方法是写消息与查消息操作的直接数据结构。 两个关键点如下：  ByteBuffer writeBuffer 如果开启了 transientStorePoolEnable,则使用 ByteBuffer.allocateDirect(fileSiz eturnBuffer public void returnBuffer(ByteBuffer byteBuffer) { byteBuffer.position(0); byteBuffer.limit(fileSize); this.availableBuffers.offerFirst(byteBuffer); } 其调用栈如下： 从上面的分析看来，并不会随着消息的不断写入而导致内存溢出。

java.nio.ByteBuffer, etc.) and is what all codecs work on. See Data Buffers and Codecs in the "Spring Core" section for more on this topic. The spring-core module provides byte[], ByteBuffer, DataBuffer and metadata values. By default only the basic codecs from spring-core for String, byte[], and ByteBuffer are registered. Adding spring-web provides access to more that can be registered as follows:

provided scope to avoid compile warnings. 435 Chapter 8. Data Buffers and Codecs Java NIO provides ByteBuffer but many libraries build their own byte buffer API on top, especially for network operations where implementations of DataBuffer can grow and shrink on demand. 2. Wrap an existing byte[] or java.nio.ByteBuffer, which decorates the given data with a DataBuffer implementation and that does not involve allocation y for others. 8.2. DataBuffer The DataBuffer interface offers similar operations as java.nio.ByteBuffer but also brings a few additional benefits some of which are inspired by the Netty ByteBuf. Below

and metadata values. By default only the basic codecs from spring-core for String, byte[], and ByteBuffer are registered. Adding spring-web provides access to more that can be registered as follows:

两个问题。 优化2 每天数百亿用户行为数据，美团点评怎么实现秒级转化分析？ - 美团技术团队 1. Unsafe调用。由于大部分的数据通过ByteBuffer访问，这里带来的额外开销对最终性能也有很大影响。Java lib中的 ByteBuffer访问接口是非常安全的，但安全也意味着低效，一次访问会有很多次的边界检查，而且多层函数的调用也 有很多额外开销。如果访问逻辑相对简单，对数据边界

信息、内存地址、持有的引用以及被持有引用的关系。 HPROF 文件映射到内存的过程： // 1. 构建内存映射的 HprofBuffer 针对大文件的一种快速的读取方式，其原理是将文件 流的通 道与 ByteBuffer 建立起关联，并只在真正发生读取时才从磁盘读取内容出来。 HprofBuffer buffer = new MemoryMappedFileBuffer(heapDumpFile); //

源码缩略不进行展示：初始化一些需要的对象 val (rdd, func) = ser.deserialize[(RDD[T], (TaskContext, Iterator[T]) => U)]( ByteBuffer.wrap(taskBinary.value), Thread.currentThread. getContextClassLoader) _executorDeserializeTime