堆缓冲区
最常用的 ByteBuf 模式是将数据存储在 JVM 的堆空间中。 这种模式被称为支撑数组
（backing array）， 它能在没有使用池化的情况下提供快速的分配和释放。
直接缓冲区
直接缓冲区的内容将驻留在常规的会被垃圾回收的堆之外。直接缓冲区对于网络数据传输是理想的选择。因为如果你的数据包含在一个在堆上分配的缓冲区中，那么事实上，在通过套接字发送它之前，JVM将会在内部把你的缓冲区复制到一个直接缓冲区中。
直接缓冲区的主要缺点是，相对于基于堆的缓冲区，它们的分配和释放都较为昂贵。所以该类型内存只在收发数据包内存使用效率较高，在netty应用层中不合适。
复合缓冲区
让我们考虑一下一个由两部分——头部和主体——组成的将通过 HTTP 协议传输的消息。这两部分由应用程序的不同模块产生， 将会在消息被发送的时候组装。该应用程序可以选择为多个消息重用相同的消息主体。当这种情况发生时，对于每个消息都将会创建一个新的头部。
因为我们不想为每个消息都重新分配这两个缓冲区，所以使用 CompositeByteBuf 是一个
完美的选择。
需要注意的是， Netty使用了CompositeByteBuf来优化套接字的I/O操作，尽可能地消除了
由JDK的缓冲区实现所导致的性能以及内存使用率的惩罚。这种优化发生在Netty的核心代码中，因此不会被暴露出来，但是你应该知道它所带来的影响。
ByteBuf 的分配方式
池化的分配 PooledByteBufAllocator是ByteBufAllocator的默认方式
可以通过 Channel（每个都可以有一个不同的 ByteBufAllocator 实例）或者绑定到
ChannelHandler 的 ChannelHandlerContext 获取一个到 ByteBufAllocator 的引用。
池化了ByteBuf的实例以提高性能并最大限度地减少内存碎片。此实现使用了一种称为jemalloc的已被大量现代操作系统所采用的高效方法来分配内存。
该方式在netty中是默认方式。
非池化的分配 UnpooledByteBufAllocator
可能某些情况下，你未能获取一个到 ByteBufAllocator 的引用。对于这种情况，Netty 提供了一个简单的称为 Unpooled 的工具类， 它提供了静态的辅助方法来创建未池化的 ByteBuf实例。
依托http进行性能测试
netty http 代码
HttpServer.java
package http.server;import org.apache.commons.logging.Log;import org.apache.commons.logging.LogFactory;import io.netty.bootstrap.ServerBootstrap;import io.netty.channel.ChannelFuture;import io.netty.channel.ChannelInitializer;import io.netty.channel.ChannelOption;import io.netty.channel.EventLoopGroup;import io.netty.channel.nio.NioEventLoopGroup;import io.netty.channel.socket.SocketChannel;import io.netty.channel.socket.nio.NioServerSocketChannel;import io.netty.handler.codec.http.HttpRequestDecoder;import io.netty.handler.codec.http.HttpResponseEncoder;public class HttpServer { ???private static Log log = LogFactory.getLog(HttpServer.class); ???????public void start(int port) throws Exception { ???????EventLoopGroup bossGroup = new NioEventLoopGroup(); ???????EventLoopGroup workerGroup = new NioEventLoopGroup(); ???????try { ???????????ServerBootstrap b = new ServerBootstrap(); ???????????b.group(bossGroup, workerGroup).channel(NioServerSocketChannel.class) ???????????????????.childHandler(new ChannelInitializer<SocketChannel>() { ???????????????????????????????@Override ???????????????????????????????public void initChannel(SocketChannel ch) throws Exception { ???????????????????????????????????// server端发送的是httpResponse，所以要使用HttpResponseEncoder进行编码 ???????????????????????????????????ch.pipeline().addLast(new HttpResponseEncoder()); ???????????????????????????????????// server端接收到的是httpRequest，所以要使用HttpRequestDecoder进行解码 ???????????????????????????????????ch.pipeline().addLast(new HttpRequestDecoder()); ???????????????????????????????????ch.pipeline().addLast(new HttpServerInboundHandler()); ???????????????????????????????} ???????????????????????????}).option(ChannelOption.SO_BACKLOG, 128) ????????????????????.childOption(ChannelOption.SO_KEEPALIVE, true); ???????????ChannelFuture f = b.bind(port).sync(); ???????????f.channel().closeFuture().sync(); ???????} finally { ???????????workerGroup.shutdownGracefully(); ???????????bossGroup.shutdownGracefully(); ???????} ???} ???public static void main(String[] args) throws Exception { ???????HttpServer server = new HttpServer(); ???????log.info("Http Server listening on 5656 ..."); ???????server.start(5656); ???}}HttpServerInboundHandler.java
package http.server;import static io.netty.handler.codec.http.HttpResponseStatus.OK;import org.apache.commons.logging.Log;import org.apache.commons.logging.LogFactory;import io.netty.buffer.ByteBuf;import io.netty.buffer.Unpooled;import io.netty.channel.ChannelHandlerContext;import io.netty.channel.ChannelInboundHandlerAdapter;import io.netty.handler.codec.http.DefaultFullHttpResponse;import io.netty.handler.codec.http.FullHttpResponse;import io.netty.handler.codec.http.HttpHeaderNames;import io.netty.handler.codec.http.HttpVersion;public class HttpServerInboundHandler extends ChannelInboundHandlerAdapter { ???private static Log log = LogFactory.getLog(HttpServerInboundHandler.class); ???// private HttpRequest request; ???// static ByteBuf buf = Unpooled.wrappedBuffer("hello world".getBytes()); ???byte[] bs = "hello world".getBytes(); ???@Override ???public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception { ???????// if (msg instanceof HttpRequest) { ???????// request = (HttpRequest) msg; ???????// ???????// String uri = request.uri(); ???????// // System.out.println("Uri:" + uri); ???????// } ???????// if (msg instanceof HttpContent) { ???????// HttpContent content = (HttpContent) msg; ???????// ByteBuf buf = content.content(); ???????// // System.out.println(buf.toString(io.netty.util.CharsetUtil.UTF_8)); ???????// buf.release(); ???????// String res = "hello world."; ???????// ByteBuf buf = Unpooled.wrappedBuffer(bs); ???????// ByteBuf buf = Unpooled.directBuffer(); ???????// ByteBuf buf = Unpooled.buffer(); ???????// ByteBuf buf = ctx.alloc().heapBuffer();// 池化堆内存 ???????// ByteBuf buf = ctx.alloc().directBuffer(); // 池化直接内存 ???????// ByteBuf buf = Unpooled.buffer();// 非池化堆内存 ???????ByteBuf buf = Unpooled.directBuffer();// 非池化堆内存 ???????buf.writeBytes(bs); ???????FullHttpResponse response = new DefaultFullHttpResponse(HttpVersion.HTTP_1_1, OK, buf); ???????// response.headers().set(HttpHeaderNames.CONTENT_TYPE, "text/plain"); ???????response.headers().set(HttpHeaderNames.CONTENT_LENGTH, response.content().readableBytes()); ???????/* ????????* if (HttpHeaders.isKeepAlive(request)) { response.headers().set(CONNECTION, Values.KEEP_ALIVE); } ????????*/ ???????ctx.write(response); ???????// ctx.flush(); ???????// } ???} ???@Override ???public void channelReadComplete(ChannelHandlerContext ctx) throws Exception { ???????ctx.flush(); ???} ???@Override ???public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) { ???????log.error(cause.getMessage()); ???????ctx.close(); ???}}池化堆内存 ctx.alloc().heapBuffer()
Running 20s test @ http://127.0.0.1:5656/ ?4 threads and 100 connections ?Thread Stats ??Avg ?????Stdev ????Max ??+/- Stdev ???Latency ????3.76ms ???9.31ms 180.34ms ??92.96% ???Req/Sec ??138.20k ???43.16k ?210.22k ???66.50% ?10957832 requests in 20.09s, 522.51MB readRequests/sec: 545332.08Transfer/sec: ????26.00MBreal ???0m20.104suser ???0m10.441ssys 0m44.703s池化直接内存 ctx.alloc().directBuffer()
Running 20s test @ http://127.0.0.1:5656/ ?4 threads and 100 connections ?Thread Stats ??Avg ?????Stdev ????Max ??+/- Stdev ???Latency ????4.47ms ???9.99ms 149.70ms ??91.76% ???Req/Sec ??138.51k ???41.31k ?209.94k ???63.38% ?10981466 requests in 20.09s, 523.64MB readRequests/sec: 546684.37Transfer/sec: ????26.07MBreal ???0m20.098suser ???0m10.890ssys 0m45.081s非池化堆内存 Unpooled.buffer()
Running 20s test @ http://127.0.0.1:5656/ ?4 threads and 100 connections ?Thread Stats ??Avg ?????Stdev ????Max ??+/- Stdev ???Latency ????4.00ms ???8.72ms 150.05ms ??91.52% ???Req/Sec ??138.84k ???42.05k ?209.72k ???63.81% ?11017442 requests in 20.09s, 525.35MB readRequests/sec: 548379.99Transfer/sec: ????26.15MBreal ???0m20.101suser ???0m10.639ssys 0m45.191s非池化直接内存 Unpooled.directBuffer()
Running 20s test @ http://127.0.0.1:5656/ ?4 threads and 100 connections ?Thread Stats ??Avg ?????Stdev ????Max ??+/- Stdev ???Latency ????3.64ms ???9.36ms 156.79ms ??92.71% ???Req/Sec ??124.55k ???33.90k ?191.90k ???71.61% ?9890536 requests in 20.07s, 471.62MB readRequests/sec: 492854.62Transfer/sec: ????23.50MBreal ???0m20.076suser ???0m9.774ssys 0m41.801s【netty这点事儿】ByteBuf 的使用模式
原文地址：https://www.cnblogs.com/xxxuwentao/p/8487236.html