通过brpc访问memecached

其他 2018-12-04 17:21:28 阅读次数: 0

memcached是一种常见的缓存服务，之前开了一个专门的博客专栏用来讲解博客。
在memecached中官网提供了client，C++的版本是libmemcached。这里我们想用brpc去替换到官方的libmemcached完成客户端client的访问，服务端的memcached当然还是一样的。

1、brpc优势

这里会给出相对于libmemcached，利用brpc写的client有以下的优势：

  • 线程安全。用户不需要为每个线程建立独立的client。
  • 支持同步、异步、半同步等访问方式，能使用ParallelChannel等组合访问方式。
  • 支持多种连接方式。支持超时、backup request、取消、tracing、内置服务等一系列brpc提供的福利。
  • 有明确的request和response。而libmemcached是没有的，收到的消息不能直接和发出的消息对应上，用户得做额外开发，而且并没有那么容易做对。

2、访问单台的memcached

创建访问memcached的channel

#include <brpc/memcache.h>
#include <brpc/channel.h>
//创建channel，注意在协议出配置为PROTOCOL_MEMCACHE，访问memcached的形式
brpc::Channel channel;
brpc::ChannelOptions options;
options.protocol = brpc::PROTOCOL_MEMCACHE;
if (channel.Init("0.0.0.0:11211", &options) != 0) {  // 11211是memcached的默认端口
   LOG(FATAL) << "Fail to init channel to memcached";
   return -1;
}
...

往memcached中设置一份数据

// 写入key="hello" value="world" flags=0xdeadbeef，10秒失效，无视cas。
brpc::MemcacheRequest request;
brpc::MemcacheResponse response;
brpc::Controller cntl;
if (!request.Set("hello", "world", 0xdeadbeef/*flags*/, 10/*expiring seconds*/, 0/*ignore cas*/)) {
    LOG(FATAL) << "Fail to SET request";
    return -1;
} 
channel.CallMethod(NULL, &cntl, &request, &response, NULL/*done*/);
if (cntl.Failed()) {
    LOG(FATAL) << "Fail to access memcached, " << cntl.ErrorText();
    return -1;
}  
if (!response.PopSet(NULL)) {
    LOG(FATAL) << "Fail to SET memcached, " << response.LastError();
    return -1;   
}
...

上述代码的说明：

  • 请求类型必须为MemcacheRequest，回复类型必须为MemcacheResponse，否则CallMethod会失败。不需要stub，直接调用channel.CallMethod，method填NULL。

  • 调用request.XXX()增加操作，本例XXX=Set，一个request多次调用不同的操作，这些操作会被同时送到memcached（常被称为pipeline模式）。

  • 依次调用response.PopXXX()弹出操作结果，本例XXX=Set，成功返回true，失败返回false，调用response.LastError()可获得错误信息。XXX必须和request的依次对应，否则失败。本例中若用PopGet就会失败，错误信息为“not a GET response"。

  • Pop结果独立于RPC结果。即使“不能把某个值设入memcached”，RPC可能还是成功的。RPC失败指连接断开，超时之类的。如果业务上认为要成功操作才算成功，那么你不仅要判RPC成功，还要判PopXXX是成功的。

3、rpc支持memcached对应的api

目前支持的请求操作有：

bool Set(const Slice& key, const Slice& value, uint32_t flags, uint32_t exptime, uint64_t cas_value);
bool Add(const Slice& key, const Slice& value, uint32_t flags, uint32_t exptime, uint64_t cas_value);
bool Replace(const Slice& key, const Slice& value, uint32_t flags, uint32_t exptime, uint64_t cas_value);
bool Append(const Slice& key, const Slice& value, uint32_t flags, uint32_t exptime, uint64_t cas_value);
bool Prepend(const Slice& key, const Slice& value, uint32_t flags, uint32_t exptime, uint64_t cas_value);
bool Delete(const Slice& key);
bool Flush(uint32_t timeout);
bool Increment(const Slice& key, uint64_t delta, uint64_t initial_value, uint32_t exptime);
bool Decrement(const Slice& key, uint64_t delta, uint64_t initial_value, uint32_t exptime);
bool Touch(const Slice& key, uint32_t exptime);
bool Version();

对应的回复操作：

// Call LastError() of the response to check the error text when any following operation fails.
bool PopGet(IOBuf* value, uint32_t* flags, uint64_t* cas_value);
bool PopGet(std::string* value, uint32_t* flags, uint64_t* cas_value);
bool PopSet(uint64_t* cas_value);
bool PopAdd(uint64_t* cas_value);
bool PopReplace(uint64_t* cas_value);
bool PopAppend(uint64_t* cas_value);
bool PopPrepend(uint64_t* cas_value);
bool PopDelete();
bool PopFlush();
bool PopIncrement(uint64_t* new_value, uint64_t* cas_value);
bool PopDecrement(uint64_t* new_value, uint64_t* cas_value);
bool PopTouch();
bool PopVersion(std::string* version);

4.实例

这里给出brpc开源的一个简单访问memcached的实例，是一个对memcached操作最简单的set get操作，具体代码如下：

#include <gflags/gflags.h>
#include <bthread/bthread.h>
#include <butil/logging.h>
#include <butil/string_printf.h>
#include <brpc/channel.h>
#include <brpc/memcache.h>
#include <brpc/policy/couchbase_authenticator.h>

DEFINE_int32(thread_num, 10, "Number of threads to send requests");
DEFINE_bool(use_bthread, false, "Use bthread to send requests");
DEFINE_bool(use_couchbase, false, "Use couchbase.");
DEFINE_string(connection_type, "", "Connection type. Available values: single, pooled, short");
DEFINE_string(server, "0.0.0.0:11211", "IP Address of server");
DEFINE_string(bucket_name, "", "Couchbase bucktet name");
DEFINE_string(bucket_password, "", "Couchbase bucket password");
DEFINE_string(load_balancer, "", "The algorithm for load balancing");
DEFINE_int32(timeout_ms, 100, "RPC timeout in milliseconds");
DEFINE_int32(max_retry, 3, "Max retries(not including the first RPC)"); 
DEFINE_bool(dont_fail, false, "Print fatal when some call failed");
DEFINE_int32(exptime, 0, "The to-be-got data will be expired after so many seconds");
DEFINE_string(key, "hello", "The key to be get");
DEFINE_string(value, "world", "The value associated with the key");
DEFINE_int32(batch, 1, "Pipelined Operations");

bvar::LatencyRecorder g_latency_recorder("client");
bvar::Adder<int> g_error_count("client_error_count");
butil::static_atomic<int> g_sender_count = BUTIL_STATIC_ATOMIC_INIT(0);

static void* sender(void* arg) {
    google::protobuf::RpcChannel* channel = 
        static_cast<google::protobuf::RpcChannel*>(arg);
    const int base_index = g_sender_count.fetch_add(1, butil::memory_order_relaxed);

    std::string value;
    std::vector<std::pair<std::string, std::string> > kvs;
    kvs.resize(FLAGS_batch);
    
	//获取key和value值
	for (int i = 0; i < FLAGS_batch; ++i) {
        kvs[i].first = butil::string_printf("%s%d", FLAGS_key.c_str(), base_index + i);
        kvs[i].second = butil::string_printf("%s%d", FLAGS_value.c_str(), base_index + i);
    }
    brpc::MemcacheRequest request;
    for (int i = 0; i < FLAGS_batch; ++i) {
        CHECK(request.Get(kvs[i].first));
    }
    while (!brpc::IsAskedToQuit()) {
        // We will receive response synchronously, safe to put variables
        // on stack.
        brpc::MemcacheResponse response;
        brpc::Controller cntl;

        // Because `done'(last parameter) is NULL, this function waits until
        // the response comes back or error occurs(including timedout).
        channel->CallMethod(NULL, &cntl, &request, &response, NULL);
        const int64_t elp = cntl.latency_us();
        //读取对应的延时
		if (!cntl.Failed()) {
            g_latency_recorder << cntl.latency_us();
            for (int i = 0; i < FLAGS_batch; ++i) {
                uint32_t flags;
                if (!response.PopGet(&value, &flags, NULL)) {
                    LOG(INFO) << "Fail to GET the key, " << response.LastError();
                    brpc::AskToQuit();
                    return NULL;
                }
                CHECK(flags == 0xdeadbeef + base_index + i)
                    << "flags=" << flags;
                CHECK(kvs[i].second == value)
                    << "base=" << base_index << " i=" << i << " value=" << value;
            }
        } else {
            g_error_count << 1; 
            CHECK(brpc::IsAskedToQuit() || !FLAGS_dont_fail)
                << "error=" << cntl.ErrorText() << " latency=" << elp;
            // We can't connect to the server, sleep a while. Notice that this
            // is a specific sleeping to prevent this thread from spinning too
            // fast. You should continue the business logic in a production 
            // server rather than sleeping.
            bthread_usleep(50000);
        }
    }
    return NULL;
}

int main(int argc, char* argv[]) {
    // Parse gflags. We recommend you to use gflags as well.
    GFLAGS_NS::ParseCommandLineFlags(&argc, &argv, true);
    if (FLAGS_exptime < 0) {
        FLAGS_exptime = 0;
    }

    // A Channel represents a communication line to a Server. Notice that 
    // Channel is thread-safe and can be shared by all threads in your program.
    brpc::Channel channel;
    
	//创建一个访问memcached的channel
    // Initialize the channel, NULL means using default options. 
    brpc::ChannelOptions options;
    options.protocol = brpc::PROTOCOL_MEMCACHE;					
    options.connection_type = FLAGS_connection_type;
    options.timeout_ms = FLAGS_timeout_ms/*milliseconds*/;
    options.max_retry = FLAGS_max_retry;
    if (FLAGS_use_couchbase && !FLAGS_bucket_name.empty()) {
        brpc::policy::CouchbaseAuthenticator* auth =
            new brpc::policy::CouchbaseAuthenticator(FLAGS_bucket_name,
                                                     FLAGS_bucket_password);
        options.auth = auth;
    }

    if (channel.Init(FLAGS_server.c_str(), FLAGS_load_balancer.c_str(), &options) != 0) {
        LOG(ERROR) << "Fail to initialize channel";
        return -1;
    }
	
	// 想memcached里面写入对应的key,value值
    // Pipeline #batch * #thread_num SET requests into memcache so that we
    // have keys to get.
    brpc::MemcacheRequest request;
    brpc::MemcacheResponse response;
    brpc::Controller cntl;
	
	//注意这里也是多个线程对memcached进行访问kv
    for (int i = 0; i < FLAGS_batch * FLAGS_thread_num; ++i) {
        if (!request.Set(butil::string_printf("%s%d", FLAGS_key.c_str(), i),
                         butil::string_printf("%s%d", FLAGS_value.c_str(), i),
                         0xdeadbeef + i, FLAGS_exptime, 0)) {
            LOG(ERROR) << "Fail to SET " << i << "th request";
            return -1;
        }
    }
	
	//调用call method去主动连接指定ip地址的memcached
    channel.CallMethod(NULL, &cntl, &request, &response, NULL);
    if (cntl.Failed()) {
        LOG(ERROR) << "Fail to access memcache, " << cntl.ErrorText();
        return -1;
    }
	
	//执行memcached中的pop操作，用来弹出访问memcached的访问操作结果。pop成功表示memcached读写成功，要不然可能rpc成功，但是业务访问不成功。
    for (int i = 0; i < FLAGS_batch * FLAGS_thread_num; ++i) {
        if (!response.PopSet(NULL)) {
            LOG(ERROR) << "Fail to SET memcache, i=" << i
                       << ", " << response.LastError();
            return -1;
        }
    }
    if (FLAGS_exptime > 0) {
        LOG(INFO) << "Set " << FLAGS_batch * FLAGS_thread_num 
                  << " values, expired after " << FLAGS_exptime << " seconds";
    } else {
        LOG(INFO) << "Set " << FLAGS_batch * FLAGS_thread_num 
                  << " values, never expired";
    }
    
	//通过多线程去访问，指定每个线程回调函数都是sender
    std::vector<bthread_t> bids;
    std::vector<pthread_t> pids;
    if (!FLAGS_use_bthread) {
        pids.resize(FLAGS_thread_num);
        for (int i = 0; i < FLAGS_thread_num; ++i) {
            if (pthread_create(&pids[i], NULL, sender, &channel) != 0) {
                LOG(ERROR) << "Fail to create pthread";
                return -1;
            }
        }
    } else {
        bids.resize(FLAGS_thread_num);
        for (int i = 0; i < FLAGS_thread_num; ++i) {
            if (bthread_start_background(
                    &bids[i], NULL, sender, &channel) != 0) {
                LOG(ERROR) << "Fail to create bthread";
                return -1;
            }
        }
    }

    while (!brpc::IsAskedToQuit()) {
        sleep(1);
        LOG(INFO) << "Accessing memcache server at qps=" << g_latency_recorder.qps(1)
                  << " latency=" << g_latency_recorder.latency(1);
    }

    LOG(INFO) << "memcache_client is going to quit";
    for (int i = 0; i < FLAGS_thread_num; ++i) {
        if (!FLAGS_use_bthread) {
            pthread_join(pids[i], NULL);
        } else {
            bthread_join(bids[i], NULL);
        }
    }
    if (options.auth) {
        delete options.auth;
    }

    return 0;
}

参考

https://github.com/brpc/brpc/blob/master/docs/cn/memcache_client.md

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