一、整体架构
Redis作为一种KV型数据库，其主要的应用方式有几种：
1、单机结构
这种情况适用于小规模的应用，安全性也相对来说比较低。处理能力有限，其数据容量也不会太大。
2、主从结构
这种方式其实就是一主多备，既可以降低Master的读压力，又可以增强安全性。但是存在主从复制的安全性问题。仍然没有解决写压力。
3、哨兵结构
通过哨兵的监控，实现了主从结构的增强即主服务器的自动灾难转移处理。这样就保证了整个系统的高可用性和安全性。增加了对系统的监控能力。但是仍然存在Master节点的写压力的问题。
4、集群结构-Proxy型
一些公司在上述的基础上增加了代理集群管理，开源了一些框架，比如Twemproxy，其实就是通过透明分片来实现多Master和多Salve。不过增加高可用的代价是，代理需要维护Failover需要自己实现。鱼和熊掌没有得兼。
5、集群结构-直连型
从Redis3.0之后支持了redis-cluster模式。其采用的是无中心结构，有点类似于P2P网络。可以自动扩展，无代理，按照哈希槽分布存储。高可用，自动实现Failover。通过Raft实现M/S的角色处理。
代码的整体架构以及代码分析，以单机及主从为主，在遇到重点流程及后期时增加其它结构类型的相关源码分析。抓住重点，理清脉络，用古人的话来说“直击肯綮”。先是整体分析，然后再根据重点的数据结构和模块进行逐一分析。
在前文提到过，Redis是一个单线程的基于多事件多路利用的C/S结构。其客户端既有官方提供的redis-cli，也有大量的第三方提供的基于其它语言的客户端。国内的各大公司几乎都封装了自己的客户端。所以，架构就说明了其流程，它一定是服务端启动监听，客户端连接并传送相关命令，然后服务端监听到数据后进行解析，丢给相关的事件处理器，然后再展开到Redis的相关处理逻辑。下面就分析其流程。
[外链图片转存失败,源站可能有防盗链机制,建议将图片保存下来直接上传(img-00AGSEf9-1576393984889)(img/redis_frame.png)]
说明：上述的图是从https://mp.weixin.qq.com/s/XJzu8yyVYZYmcOui_xXnvw中截取，如有侵权，请告知删除。
二、流程
1、客户端
老样子，先看代码：
int main(int argc, char **argv) {
int firstarg;
//相关的配置文件省略
config.hostip = sdsnew("127.0.0.1");
config.hostport = 6379;
......
config.cluster_manager_command.timeout = CLUSTER_MANAGER_MIGRATE_TIMEOUT;
config.cluster_manager_command.pipeline = CLUSTER_MANAGER_MIGRATE_PIPELINE;
config.cluster_manager_command.threshold =
CLUSTER_MANAGER_REBALANCE_THRESHOLD;
config.cluster_manager_command.backup_dir = NULL;
pref.hints = 1;
spectrum_palette = spectrum_palette_color;
spectrum_palette_size = spectrum_palette_color_size;
if (!isatty(fileno(stdout)) && (getenv("FAKETTY") == NULL))
config.output = OUTPUT_RAW;
else
config.output = OUTPUT_STANDARD;
config.mb_delim = sdsnew("\n");
firstarg = parseOptions(argc,argv);
argc -= firstarg;
argv += firstarg;
parseEnv();
// Cluster Manager mode
if (CLUSTER_MANAGER_MODE()) {
clusterManagerCommandProc \*proc = validateClusterManagerCommand();
if (!proc) {
sdsfree(config.hostip);
sdsfree(config.mb_delim);
exit(1);
}
clusterManagerMode(proc);
}
// Latency mode
if (config.latency_mode) {
if (cliConnect(0) == REDIS_ERR) exit(1);
latencyMode();
}
// Latency distribution mode
if (config.latency_dist_mode) {
if (cliConnect(0) == REDIS_ERR) exit(1);
latencyDistMode();
}
// Slave mode
if (config.slave_mode) {
if (cliConnect(0) == REDIS_ERR) exit(1);
sendCapa();
slaveMode();
}
// Get RDB mode.
if (config.getrdb_mode) {
if (cliConnect(0) == REDIS_ERR) exit(1);
sendCapa();
getRDB(NULL);
}
// Pipe mode
if (config.pipe_mode) {
if (cliConnect(0) == REDIS_ERR) exit(1);
pipeMode();
}
// Find big keys
if (config.bigkeys) {
if (cliConnect(0) == REDIS_ERR) exit(1);
findBigKeys(0, 0);
}
// Find large keys
if (config.memkeys) {
if (cliConnect(0) == REDIS_ERR) exit(1);
findBigKeys(1, config.memkeys_samples);
}
// Find hot keys
if (config.hotkeys) {
if (cliConnect(0) == REDIS_ERR) exit(1);
findHotKeys();
}
// Stat mode
if (config.stat_mode) {
if (cliConnect(0) == REDIS_ERR) exit(1);
if (config.interval == 0) config.interval = 1000000;
statMode();
}
// Scan mode
if (config.scan_mode) {
if (cliConnect(0) == REDIS_ERR) exit(1);
scanMode();
}
// LRU test mode
if (config.lru_test_mode) {
if (cliConnect(0) == REDIS_ERR) exit(1);
LRUTestMode();
}
// Intrinsic latency mode
if (config.intrinsic_latency_mode) intrinsicLatencyMode();
// Start interactive mode when no command is provided
if (argc == 0 && !config.eval) {
// Ignore SIGPIPE in interactive mode to force a reconnect
signal(SIGPIPE, SIG_IGN);
// Note that in repl mode we don't abort on connection error.
// A new attempt will be performed for every command send.
cliConnect(0);
repl(); //传输命令
}
// Otherwise, we have some arguments to execute
if (cliConnect(0) != REDIS_OK) exit(1);
if (config.eval) {
return evalMode(argc,argv);
} else {
return noninteractive(argc,convertToSds(argc,argv));
}
}
因为是c程序，所以一定会是在main函数里启动。在这个函数里，其实只有三大部分，配置参数的设定，参数命令解析和模式选择。在模式选择中进行网络连接和模式设置以及需要发送相关的信号。先看一下参数解析的函数parseOptions：
static int parseOptions(int argc, char **argv) {
int i;
for (i = 1; i < argc; i++) {
int lastarg = i==argc-1;
if (!strcmp(argv[i],"-h") && !lastarg) {
sdsfree(config.hostip);
config.hostip = sdsnew(argv[++i]);
} else if (!strcmp(argv[i],"-h") && lastarg) {
usage();
}
......
} else if (!strcmp(argv[i],"-v") || !strcmp(argv[i], "--version")) {
sds version = cliVersion();
printf("redis-cli %s\n", version);
sdsfree(version);
exit(0);
} else if (!strcmp(argv[i],"-3")) {
config.resp3 = 1;
} else if (CLUSTER_MANAGER_MODE() && argv[i][0] != '-') {
if (config.cluster_manager_command.argc == 0) {
int j = i + 1;
while (j < argc && argv[j][0] != '-') j++;
int cmd_argc = j - i;
config.cluster_manager_command.argc = cmd_argc;
config.cluster_manager_command.argv = argv + i;
if (cmd_argc > 1) i = j - 1;
}
} else {
if (argv[i][0] == '-') {
fprintf(stderr,
"Unrecognized option or bad number of args for: '%s'\n",
argv[i]);
exit(1);
} else {
// Likely the command name, stop here.
break;
}
}
}
// --ldb requires --eval.
if (config.eval_ldb && config.eval == NULL) {
fprintf(stderr,"Options --ldb and --ldb-sync-mode require --eval.\n");
fprintf(stderr,"Try %s --help for more information.\n", argv[0]);
exit(1);
}
if (!config.no_auth_warning && config.auth != NULL) {
fputs("Warning: Using a password with '-a' or '-u' option on the command"
" line interface may not be safe.\n", stderr);
}
return i;
}
//其中一个调用的函数，可以看到命令的参数形式
static void usage(void) {
sds version = cliVersion();
fprintf(stderr,
"redis-cli %s\n"
"\n"
"Usage: redis-cli [OPTIONS] [cmd [arg [arg ...]]]\n"
" -h <hostname> Server hostname (default: 127.0.0.1).\n"
" -p <port> Server port (default: 6379).\n"
" -s <socket> Server socket (overrides hostname and port).\n"
" -a <password> Password to use when connecting to the server.\n"
" You can also use the " REDIS_CLI_AUTH_ENV " environment\n"
" variable to pass this password more safely\n"
" (if both are used, this argument takes predecence).\n"
" -user <username> Used to send ACL style 'AUTH username pass'. Needs -a.\n"
" -pass <password> Alias of -a for consistency with the new --user option.\n"
" -u <uri> Server URI.\n"
" -r <repeat> Execute specified command N times.\n"
" -i <interval> When -r is used, waits <interval> seconds per command.\n"
" It is possible to specify sub-second times like -i 0.1.\n"
" -n <db> Database number.\n"
" -3 Start session in RESP3 protocol mode.\n"
" -x Read last argument from STDIN.\n"
" -d <delimiter> Multi-bulk delimiter in for raw formatting (default: \\n).\n"
" -c Enable cluster mode (follow -ASK and -MOVED redirections).\n"
#ifdef USE_OPENSSL
" --tls Establish a secure TLS connection.\n"
" --cacert CA Certificate file to verify with.\n"
" --cacertdir Directory where trusted CA certificates are stored.\n"
" If neither cacert nor cacertdir are specified, the default\n"
" system-wide trusted root certs configuration will apply.\n"
" --cert Client certificate to authenticate with.\n"
" --key Private key file to authenticate with.\n"
#endif
" --raw Use raw formatting for replies (default when STDOUT is\n"
" not a tty).\n"
" --no-raw Force formatted output even when STDOUT is not a tty.\n"
" --csv Output in CSV format.\n"
" --stat Print rolling stats about server: mem, clients, ...\n"
" --latency Enter a special mode continuously sampling latency.\n"
" If you use this mode in an interactive session it runs\n"
" forever displaying real-time stats. Otherwise if --raw or\n"
" --csv is specified, or if you redirect the output to a non\n"
" TTY, it samples the latency for 1 second (you can use\n"
" -i to change the interval), then produces a single output\n"
" and exits.\n",version);
fprintf(stderr,
" --latency-history Like --latency but tracking latency changes over time.\n"
" Default time interval is 15 sec. Change it using -i.\n"
" --latency-dist Shows latency as a spectrum, requires xterm 256 colors.\n"
" Default time interval is 1 sec. Change it using -i.\n"
" --lru-test <keys> Simulate a cache workload with an 80-20 distribution.\n"
" --replica Simulate a replica showing commands received from the master.\n"
" --rdb <filename> Transfer an RDB dump from remote server to local file.\n"
" --pipe Transfer raw Redis protocol from stdin to server.\n"
" --pipe-timeout <n> In --pipe mode, abort with error if after sending all data.\n"
" no reply is received within <n> seconds.\n"
" Default timeout: %d. Use 0 to wait forever.\n",
REDIS_CLI_DEFAULT_PIPE_TIMEOUT);
fprintf(stderr,
" --bigkeys Sample Redis keys looking for keys with many elements (complexity).\n"
" --memkeys Sample Redis keys looking for keys consuming a lot of memory.\n"
" --memkeys-samples <n> Sample Redis keys looking for keys consuming a lot of memory.\n"
" And define number of key elements to sample\n"
" --hotkeys Sample Redis keys looking for hot keys.\n"
" only works when maxmemory-policy is \*lfu.\n"
" --scan List all keys using the SCAN command.\n"
" --pattern <pat> Useful with --scan to specify a SCAN pattern.\n"
" --intrinsic-latency <sec> Run a test to measure intrinsic system latency.\n"
" The test will run for the specified amount of seconds.\n"
" --eval <file> Send an EVAL command using the Lua script at <file>.\n"
" --ldb Used with --eval enable the Redis Lua debugger.\n"
" --ldb-sync-mode Like --ldb but uses the synchronous Lua debugger, in\n"
" this mode the server is blocked and script changes are\n"
" not rolled back from the server memory.\n"
" --cluster <command> [args...] [opts...]\n"
" Cluster Manager command and arguments (see below).\n"
" --verbose Verbose mode.\n"
" --no-auth-warning Don't show warning message when using password on command\n"
" line interface.\n"
" --help Output this help and exit.\n"
" --version Output version and exit.\n"
"\n");
// Using another fprintf call to avoid -Woverlength-strings compile warning
fprintf(stderr,
"Cluster Manager Commands:\n"
" Use --cluster help to list all available cluster manager commands.\n"
"\n"
"Examples:\n"
" cat /etc/passwd | redis-cli -x set mypasswd\n"
" redis-cli get mypasswd\n"
" redis-cli -r 100 lpush mylist x\n"
" redis-cli -r 100 -i 1 info | grep used_memory_human:\n"
" redis-cli --eval myscript.lua key1 key2 , arg1 arg2 arg3\n"
" redis-cli --scan --pattern '*:12345*'\n"
"\n"
" (Note: when using --eval the comma separates KEYS[] from ARGV[] items)\n"
"\n"
"When no command is given, redis-cli starts in interactive mode.\n"
"Type \"help\" in interactive mode for information on available commands\n"
"and settings.\n"
"\n");
sdsfree(version);
exit(1);
}
再看一个网络连接的函数cliConnect：
static int cliConnect(int flags) {
if (context == NULL || flags & CC_FORCE) {
if (context != NULL) {
redisFree(context);
}
if (config.hostsocket == NULL) {
context = redisConnect(config.hostip,config.hostport);
} else {
context = redisConnectUnix(config.hostsocket);
}
if (!context->err && config.tls) {
const char \*err = NULL;
if (cliSecureConnection(context, &err) == REDIS_ERR && err) {
fprintf(stderr, "Could not negotiate a TLS connection: %s\n", err);
context = NULL;
redisFree(context);
return REDIS_ERR;
}
}
if (context->err) {
if (!(flags & CC_QUIET)) {
fprintf(stderr,"Could not connect to Redis at ");
if (config.hostsocket == NULL)
fprintf(stderr,"%s:%d: %s\n",
config.hostip,config.hostport,context->errstr);
else
fprintf(stderr,"%s: %s\n",
config.hostsocket,context->errstr);
}
redisFree(context);
context = NULL;
return REDIS_ERR;
}
// Set aggressive KEEP_ALIVE socket option in the Redis context socket
// in order to prevent timeouts caused by the execution of long
// commands. At the same time this improves the detection of real
// errors.
anetKeepAlive(NULL, context->fd, REDIS_CLI_KEEPALIVE_INTERVAL);
// Do AUTH, select the right DB, switch to RESP3 if needed.
if (cliAuth() != REDIS_OK)
return REDIS_ERR;
if (cliSelect() != REDIS_OK)
return REDIS_ERR;
if (cliSwitchProto() != REDIS_OK)
return REDIS_ERR;
}
return REDIS_OK;
}
这段代码开始首先判断使用的上下文是否存在，如果存在就释放掉。然后根据hostsocket的类型来判断生成基于TCP还是UNIX来生成。它们最终都会调用redisConnectWithOptions函数来连接服务器：
redisContext \*redisConnectWithOptions(const redisOptions *options) {
redisContext \*c = redisContextInit(options);
if (c == NULL) {
return NULL;
}
if (!(options->options & REDIS_OPT_NONBLOCK)) {
c->flags |= REDIS_BLOCK;
}
if (options->options & REDIS_OPT_REUSEADDR) {
c->flags |= REDIS_REUSEADDR;
}
if (options->options & REDIS_OPT_NOAUTOFREE) {
c->flags |= REDIS_NO_AUTO_FREE;
}
if (options->type == REDIS_CONN_TCP) {
redisContextConnectBindTcp(c, options->endpoint.tcp.ip,
options->endpoint.tcp.port, options->timeout,
options->endpoint.tcp.source_addr);
} else if (options->type == REDIS_CONN_UNIX) {
redisContextConnectUnix(c, options->endpoint.unix_socket,
options->timeout);
} else if (options->type == REDIS_CONN_USERFD) {
c->fd = options->endpoint.fd;
c->flags |= REDIS_CONNECTED;
} else {
// Unknown type - FIXME - FREE
return NULL;
}
if (options->timeout != NULL && (c->flags & REDIS_BLOCK) && c->fd != REDIS_INVALID_FD) {
redisContextSetTimeout(c, *options->timeout);
}
return c;
}
最终在_redisContextConnectTcp这个函数中绑定相关的服务，并调用常见的网络连接函数：
if (connect(s,p->ai_addr,p->ai_addrlen) == -1) {
......
}
看一下Repl，这个函数会具体的把相关的命令和数据传输到报备端。
static void repl(void) {
sds historyfile = NULL;
int history = 0;
char \*line;
int argc;
sds \*argv;
// Initialize the help and, if possible, use the COMMAND command in order
// to retrieve missing entries.
cliInitHelp();
cliIntegrateHelp();
config.interactive = 1;
linenoiseSetMultiLine(1);
linenoiseSetCompletionCallback(completionCallback);
linenoiseSetHintsCallback(hintsCallback);
linenoiseSetFreeHintsCallback(freeHintsCallback);
// Only use history and load the rc file when stdin is a tty.
if (isatty(fileno(stdin))) {
historyfile = getDotfilePath(REDIS_CLI_HISTFILE_ENV,REDIS_CLI_HISTFILE_DEFAULT);
//keep in-memory history always regardless if history file can be determined
history = 1;
if (historyfile != NULL) {
linenoiseHistoryLoad(historyfile);
}
cliLoadPreferences();
}
cliRefreshPrompt();
while((line = linenoise(context ? config.prompt : "not connected> ")) != NULL) {
if (line[0] != '\0') {
long repeat = 1;
int skipargs = 0;
char \*endptr = NULL;
argv = cliSplitArgs(line,&argc);
// check if we have a repeat command option and
//need to skip the first arg
if (argv && argc > 0) {
errno = 0;
repeat = strtol(argv[0], &endptr, 10);
if (argc > 1 && *endptr == '\0') {
if (errno == ERANGE || errno == EINVAL || repeat <= 0) {
fputs("Invalid redis-cli repeat command option value.\n", stdout);
sdsfreesplitres(argv, argc);
linenoiseFree(line);
continue;
}
skipargs = 1;
} else {
repeat = 1;
}
}
// Won't save auth command in history file
if (!(argv && argc > 0 && !strcasecmp(argv[0+skipargs], "auth"))) {
if (history) linenoiseHistoryAdd(line);
if (historyfile) linenoiseHistorySave(historyfile);
}
if (argv == NULL) {
printf("Invalid argument(s)\n");
linenoiseFree(line);
continue;
} else if (argc > 0) {
if (strcasecmp(argv[0],"quit") == 0 ||
strcasecmp(argv[0],"exit") == 0)
{
exit(0);
} else if (argv[0][0] == ':') {
cliSetPreferences(argv,argc,1);
sdsfreesplitres(argv,argc);
linenoiseFree(line);
continue;
} else if (strcasecmp(argv[0],"restart") == 0) {
if (config.eval) {
config.eval_ldb = 1;
config.output = OUTPUT_RAW;
return; //Return to evalMode to restart the session.
} else {
printf("Use 'restart' only in Lua debugging mode.");
}
} else if (argc == 3 && !strcasecmp(argv[0],"connect")) {
sdsfree(config.hostip);
config.hostip = sdsnew(argv[1]);
config.hostport = atoi(argv[2]);
cliRefreshPrompt();
cliConnect(CC_FORCE);
} else if (argc == 1 && !strcasecmp(argv[0],"clear")) {
linenoiseClearScreen();
} else {
long long start_time = mstime(), elapsed;
issueCommandRepeat(argc-skipargs, argv+skipargs, repeat);
// If our debugging session ended, show the EVAL final
//reply
if (config.eval_ldb_end) {
config.eval_ldb_end = 0;
cliReadReply(0);
printf("\n(Lua debugging session ended%s)\n\n",
config.eval_ldb_sync ? "" :
" -- dataset changes rolled back");
}
elapsed = mstime()-start_time;
if (elapsed >= 500 &&
config.output == OUTPUT_STANDARD)
{
printf("(%.2fs)\n",(double)elapsed/1000);
}
}
}
// Free the argument vector
sdsfreesplitres(argv,argc);
}
// linenoise() returns malloc-ed lines like readline()
linenoiseFree(line);
}
exit(0);
}
从代码中可以看到。其使用linenoise 这款优秀的命令行编辑库来接收输入。然后经issueCommandRepeat传送至cliSendCommand进行特殊命令的解析。
static int cliSendCommand(int argc, char **argv, long repeat) {
char \*command = argv[0];
size_t \*argvlen;
int j, output_raw;
if (!config.eval_ldb && // In debugging mode, let's pass "help" to Redis.
(!strcasecmp(command,"help") || !strcasecmp(command,"?"))) {
cliOutputHelp(--argc, ++argv);
return REDIS_OK;
}
if (context == NULL) return REDIS_ERR;
output_raw = 0;
if (!strcasecmp(command,"info") ||
!strcasecmp(command,"lolwut") ||
(argc >= 2 && !strcasecmp(command,"debug") &&
!strcasecmp(argv[1],"htstats")) ||
(argc >= 2 && !strcasecmp(command,"debug") &&
!strcasecmp(argv[1],"htstats-key")) ||
(argc >= 2 && !strcasecmp(command,"memory") &&
(!strcasecmp(argv[1],"malloc-stats") ||
!strcasecmp(argv[1],"doctor"))) ||
(argc == 2 && !strcasecmp(command,"cluster") &&
(!strcasecmp(argv[1],"nodes") ||
!strcasecmp(argv[1],"info"))) ||
(argc >= 2 && !strcasecmp(command,"client") &&
!strcasecmp(argv[1],"list")) ||
(argc == 3 && !strcasecmp(command,"latency") &&
!strcasecmp(argv[1],"graph")) ||
(argc == 2 && !strcasecmp(command,"latency") &&
!strcasecmp(argv[1],"doctor")))
{
output_raw = 1;
}
......
// Negative repeat is allowed and causes infinite loop,
works well with the interval option.
while(repeat < 0 || repeat-- > 0) {
redisAppendCommandArgv(context,argc,(const char**)argv,argvlen);
while (config.monitor_mode) {
if (cliReadReply(output_raw) != REDIS_OK) exit(1);
fflush(stdout);
}
......
if (config.slave_mode) {
printf("Entering replica output mode... (press Ctrl-C to quit)\n");
slaveMode();
config.slave_mode = 0;
zfree(argvlen);
return REDIS_ERR; // Error = slaveMode lost connection to master
}
if (cliReadReply(output_raw) != REDIS_OK) {
zfree(argvlen);
return REDIS_ERR;
} else {
......
}
zfree(argvlen);
return REDIS_OK;
}
这样基本的客户端的流程就运行起来了。
2、服务端
服务端也要从主函数开始：
int main(int argc, char **argv) {
struct timeval tv;
int j;
......
#ifdef INIT_SETPROCTITLE_REPLACEMENT
spt_init(argc, argv);
#endif
setlocale(LC_COLLATE,"");
tzset();
zmalloc_set_oom_handler(redisOutOfMemoryHandler);
srand(time(NULL)^getpid());
gettimeofday(&tv,NULL);
uint8_t hashseed[16];
getRandomBytes(hashseed,sizeof(hashseed));
dictSetHashFunctionSeed(hashseed);
server.sentinel_mode = checkForSentinelMode(argc,argv);
initServerConfig();
ACLInit();
moduleInitModulesSystem();
tlsInit();
server.executable = getAbsolutePath(argv[0]);
server.exec_argv = zmalloc(sizeof(char*)*(argc+1));
server.exec_argv[argc] = NULL;
for (j = 0; j < argc; j++) server.exec_argv[j] = zstrdup(argv[j]);
if (server.sentinel_mode) {
initSentinelConfig();
initSentinel();
}
if (strstr(argv[0],"redis-check-rdb") != NULL)
redis_check_rdb_main(argc,argv,NULL);
else if (strstr(argv[0],"redis-check-aof") != NULL)
redis_check_aof_main(argc,argv);
if (argc >= 2) {
j = 1;
sds options = sdsempty();
char \*configfile = NULL;
if (strcmp(argv[1], "-v") == 0 ||
strcmp(argv[1], "--version") == 0) version();
if (strcmp(argv[1], "--help") == 0 ||
strcmp(argv[1], "-h") == 0) usage();
if (strcmp(argv[1], "--test-memory") == 0) {
if (argc == 3) {
memtest(atoi(argv[2]),50);
exit(0);
} else {
fprintf(stderr,"Please specify the amount of memory to test in megabytes.\n");
fprintf(stderr,"Example: ./redis-server --test-memory 4096\n\n");
exit(1);
}
}
if (argv[j][0] != '-' || argv[j][1] != '-') {
configfile = argv[j];
server.configfile = getAbsolutePath(configfile);
zfree(server.exec_argv[j]);
server.exec_argv[j] = zstrdup(server.configfile);
j++;
}
while(j != argc) {
if (argv[j][0] == '-' && argv[j][1] == '-') {
if (!strcmp(argv[j], "--check-rdb")) {
j++;
continue;
}
if (sdslen(options)) options = sdscat(options,"\n");
options = sdscat(options,argv[j]+2);
options = sdscat(options," ");
} else {
options = sdscatrepr(options,argv[j],strlen(argv[j]));
options = sdscat(options," ");
}
j++;
}
if (server.sentinel_mode && configfile && *configfile == '-') {
serverLog(LL_WARNING,
"Sentinel config from STDIN not allowed.");
serverLog(LL_WARNING,
"Sentinel needs config file on disk to save state. Exiting...");
exit(1);
}
resetServerSaveParams();
loadServerConfig(configfile,options);
sdsfree(options);
}
serverLog(LL_WARNING, "oO0OoO0OoO0Oo Redis is starting oO0OoO0OoO0Oo");
serverLog(LL_WARNING,
"Redis version=%s, bits=%d, commit=%s, modified=%d, pid=%d, just started",
REDIS_VERSION,
(sizeof(long) == 8) ? 64 : 32,
redisGitSHA1(),
strtol(redisGitDirty(),NULL,10) > 0,
(int)getpid());
if (argc == 1) {
serverLog(LL_WARNING, "Warning: no config file specified, using the default config. In order to specify a config file use %s /path/to/%s.conf", argv[0], server.sentinel_mode ? "sentinel" : "redis");
} else {
serverLog(LL_WARNING, "Configuration loaded");
}
server.supervised = redisIsSupervised(server.supervised_mode);
int background = server.daemonize && !server.supervised;
if (background) daemonize();
initServer();
if (background || server.pidfile) createPidFile();
redisSetProcTitle(argv[0]);
redisAsciiArt();
checkTcpBacklogSettings();
if (!server.sentinel_mode) {
serverLog(LL_WARNING,"Server initialized");
#ifdef __linux__
linuxMemoryWarnings();
#endif
moduleLoadFromQueue();
ACLLoadUsersAtStartup();
InitServerLast();
loadDataFromDisk();
if (server.cluster_enabled) {
if (verifyClusterConfigWithData() == C_ERR) {
serverLog(LL_WARNING,
"You can't have keys in a DB different than DB 0 when in "
"Cluster mode. Exiting.");
exit(1);
}
}
if (server.ipfd_count > 0 || server.tlsfd_count > 0)
serverLog(LL_NOTICE,"Ready to accept connections");
if (server.sofd > 0)
serverLog(LL_NOTICE,"The server is now ready to accept connections at %s", server.unixsocket);
} else {
InitServerLast();
sentinelIsRunning();
}
if (server.maxmemory > 0 && server.maxmemory < 1024*1024) {
serverLog(LL_WARNING,"WARNING: You specified a maxmemory value that is less than 1MB (current value is %llu bytes). Are you sure this is what you really want?", server.maxmemory);
}
aeSetBeforeSleepProc(server.el,beforeSleep);
aeSetAfterSleepProc(server.el,afterSleep);
aeMain(server.el);
aeDeleteEventLoop(server.el);
return 0;
}
服务端的代码相对来说要启动的多一些，要把各种情况下的参数都要进行判断然后分别进行初始化，配置相关的处理句柄，比如哨兵和Panic的相关处理配置。然后同样是参数的处理，服务端是有日志管理 的，所以如果有什么异常都要写入日志中。如果设置为后台运行就启动为守护进程。它创建子进程的方法就两行代码：
void daemonize(void) {
int fd;
if (fork() != 0) exit(0);
setsid();
......
}
然后看一下initServer：
void initServer(void) {
int j;
signal(SIGHUP, SIG_IGN);
signal(SIGPIPE, SIG_IGN);
setupSignalHandlers();
if (server.syslog_enabled) {
openlog(server.syslog_ident, LOG_PID | LOG_NDELAY | LOG_NOWAIT,
server.syslog_facility);
}
server.hz = server.config_hz;
server.pid = getpid();
server.current_client = NULL;
server.fixed_time_expire = 0;
server.clients = listCreate();
server.clients_index = raxNew();
server.clients_to_close = listCreate();
server.slaves = listCreate();
server.monitors = listCreate();
server.clients_pending_write = listCreate();
server.clients_pending_read = listCreate();
server.slaveseldb = -1;
server.unblocked_clients = listCreate();
server.ready_keys = listCreate();
server.clients_waiting_acks = listCreate();
server.get_ack_from_slaves = 0;
server.clients_paused = 0;
server.system_memory_size = zmalloc_get_memory_size();
if (server.tls_port && tlsConfigure(&server.tls_ctx_config) == C_ERR) {
serverLog(LL_WARNING, "Failed to configure TLS. Check logs for more info.");
exit(1);
}
createSharedObjects();
adjustOpenFilesLimit();
server.el = aeCreateEventLoop(server.maxclients+CONFIG_FDSET_INCR);
if (server.el == NULL) {
serverLog(LL_WARNING,
"Failed creating the event loop. Error message: '%s'",
strerror(errno));
exit(1);
}
server.db = zmalloc(sizeof(redisDb)*server.dbnum);
if (server.port != 0 &&
listenToPort(server.port,server.ipfd,&server.ipfd_count) == C_ERR)
exit(1);
if (server.tls_port != 0 &&
listenToPort(server.tls_port,server.tlsfd,&server.tlsfd_count) == C_ERR)
exit(1);
if (server.unixsocket != NULL) {
unlink(server.unixsocket);
server.sofd = anetUnixServer(server.neterr,server.unixsocket,
server.unixsocketperm, server.tcp_backlog);
if (server.sofd == ANET_ERR) {
serverLog(LL_WARNING, "Opening Unix socket: %s", server.neterr);
exit(1);
}
anetNonBlock(NULL,server.sofd);
}
if (server.ipfd_count == 0 && server.tlsfd_count == 0 && server.sofd < 0) {
serverLog(LL_WARNING, "Configured to not listen anywhere, exiting.");
exit(1);
}
for (j = 0; j < server.dbnum; j++) {
server.db[j].dict = dictCreate(&dbDictType,NULL);
server.db[j].expires = dictCreate(&keyptrDictType,NULL);
server.db[j].expires_cursor = 0;
server.db[j].blocking_keys = dictCreate(&keylistDictType,NULL);
server.db[j].ready_keys = dictCreate(&objectKeyPointerValueDictType,NULL);
server.db[j].watched_keys = dictCreate(&keylistDictType,NULL);
server.db[j].id = j;
server.db[j].avg_ttl = 0;
server.db[j].defrag_later = listCreate();
listSetFreeMethod(server.db[j].defrag_later,(void (*)(void*))sdsfree);
}
evictionPoolAlloc();
server.pubsub_channels = dictCreate(&keylistDictType,NULL);
server.pubsub_patterns = listCreate();
listSetFreeMethod(server.pubsub_patterns,freePubsubPattern);
listSetMatchMethod(server.pubsub_patterns,listMatchPubsubPattern);
server.cronloops = 0;
server.rdb_child_pid = -1;
server.aof_child_pid = -1;
server.module_child_pid = -1;
server.rdb_child_type = RDB_CHILD_TYPE_NONE;
server.rdb_pipe_conns = NULL;
server.rdb_pipe_numconns = 0;
server.rdb_pipe_numconns_writing = 0;
server.rdb_pipe_buff = NULL;
server.rdb_pipe_bufflen = 0;
server.rdb_bgsave_scheduled = 0;
server.child_info_pipe[0] = -1;
server.child_info_pipe[1] = -1;
server.child_info_data.magic = 0;
aofRewriteBufferReset();
server.aof_buf = sdsempty();
server.lastsave = time(NULL);
server.lastbgsave_try = 0;
server.rdb_save_time_last = -1;
server.rdb_save_time_start = -1;
server.dirty = 0;
resetServerStats();
server.stat_starttime = time(NULL);
server.stat_peak_memory = 0;
server.stat_rdb_cow_bytes = 0;
server.stat_aof_cow_bytes = 0;
server.stat_module_cow_bytes = 0;
server.cron_malloc_stats.zmalloc_used = 0;
server.cron_malloc_stats.process_rss = 0;
server.cron_malloc_stats.allocator_allocated = 0;
server.cron_malloc_stats.allocator_active = 0;
server.cron_malloc_stats.allocator_resident = 0;
server.lastbgsave_status = C_OK;
server.aof_last_write_status = C_OK;
server.aof_last_write_errno = 0;
server.repl_good_slaves_count = 0;
if (aeCreateTimeEvent(server.el, 1, serverCron, NULL, NULL) == AE_ERR) {
serverPanic("Can't create event loop timers.");
exit(1);
}
for (j = 0; j < server.ipfd_count; j++) {
if (aeCreateFileEvent(server.el, server.ipfd[j], AE_READABLE,
acceptTcpHandler,NULL) == AE_ERR)
{
serverPanic(
"Unrecoverable error creating server.ipfd file event.");
}
}
for (j = 0; j < server.tlsfd_count; j++) {
if (aeCreateFileEvent(server.el, server.tlsfd[j], AE_READABLE,
acceptTLSHandler,NULL) == AE_ERR)
{
serverPanic(
"Unrecoverable error creating server.tlsfd file event.");
}
}
if (server.sofd > 0 && aeCreateFileEvent(server.el,server.sofd,AE_READABLE,
acceptUnixHandler,NULL) == AE_ERR) serverPanic("Unrecoverable error creating server.sofd file event.");
if (aeCreateFileEvent(server.el, server.module_blocked_pipe[0], AE_READABLE,
moduleBlockedClientPipeReadable,NULL) == AE_ERR) {
serverPanic(
"Error registering the readable event for the module "
"blocked clients subsystem.");
}
if (server.aof_state == AOF_ON) {
server.aof_fd = open(server.aof_filename,
O_WRONLY|O_APPEND|O_CREAT,0644);
if (server.aof_fd == -1) {
serverLog(LL_WARNING, "Can't open the append-only file: %s",
strerror(errno));
exit(1);
}
}
if (server.arch_bits == 32 && server.maxmemory == 0) {
serverLog(LL_WARNING,"Warning: 32 bit instance detected but no memory limit set. Setting 3 GB maxmemory limit with 'noeviction' policy now.");
server.maxmemory = 3072LL*(1024*1024);
server.maxmemory_policy = MAXMEMORY_NO_EVICTION;
}
if (server.cluster_enabled) clusterInit();
replicationScriptCacheInit();
scriptingInit(1);
slowlogInit();
latencyMonitorInit();
}
同样是配置一大批的参数，然后创建共享对象（后面会分析），调整文件限制。然后网络监听：
int listenToPort(int port, int *fds, int *count) {
int j;
if (server.bindaddr_count == 0) server.bindaddr[0] = NULL;
for (j = 0; j < server.bindaddr_count || j == 0; j++) {
if (server.bindaddr[j] == NULL) {
int unsupported = 0;
fds[\*count] = anetTcp6Server(server.neterr,port,NULL,
server.tcp_backlog);
if (fds[*count] != ANET_ERR) {
anetNonBlock(NULL,fds[*count]);
(\*count)++;
} else if (errno == EAFNOSUPPORT) {
unsupported++;
serverLog(LL_WARNING,"Not listening to IPv6: unsupported");
}
if (*count == 1 || unsupported) {
fds[\*count] = anetTcpServer(server.neterr,port,NULL,
server.tcp_backlog);
if (fds[*count] != ANET_ERR) {
anetNonBlock(NULL,fds[*count]);
(\*count)++;
} else if (errno == EAFNOSUPPORT) {
unsupported++;
serverLog(LL_WARNING,"Not listening to IPv4: unsupported");
}
}
if (*count + unsupported == 2) break;
} else if (strchr(server.bindaddr[j],':')) {
fds[\*count] = anetTcp6Server(server.neterr,port,server.bindaddr[j],
server.tcp_backlog);
} else {
fds[\*count] = anetTcpServer(server.neterr,port,server.bindaddr[j],
server.tcp_backlog);
}
if (fds[*count] == ANET_ERR) {
serverLog(LL_WARNING,
"Could not create server TCP listening socket %s:%d: %s",
server.bindaddr[j] ? server.bindaddr[j] : "*",
port, server.neterr);
if (errno == ENOPROTOOPT || errno == EPROTONOSUPPORT ||
errno == ESOCKTNOSUPPORT || errno == EPFNOSUPPORT ||
errno == EAFNOSUPPORT || errno == EADDRNOTAVAIL)
continue;
return C_ERR;
}
anetNonBlock(NULL,fds[*count]);
(\*count)++;
}
return C_OK;
}
在这个函数里分别创建基于IPV4和IPV6的连接。处理各种异常，设置默认的非阻塞参数。这种方式根据实际的配置不同会产生几种不同的设置的方法，比如TCP或是UNIX，有没有TLS等。其后开始创建数据库并初始化相关状态。然后创建事件处理的句柄：
int aeCreateFileEvent(aeEventLoop *eventLoop, int fd, int mask,
aeFileProc *proc, void *clientData)
{
if (fd >= eventLoop->setsize) {
errno = ERANGE;
return AE_ERR;
}
aeFileEvent \*fe = &eventLoop->events[fd];
if (aeApiAddEvent(eventLoop, fd, mask) == -1)
return AE_ERR;
fe->mask |= mask;
if (mask & AE_READABLE) fe->rfileProc = proc;
if (mask & AE_WRITABLE) fe->wfileProc = proc;
fe->clientData = clientData;
if (fd > eventLoop->maxfd)
eventLoop->maxfd = fd;
return AE_OK;
}
void acceptTcpHandler(aeEventLoop *el, int fd, void *privdata, int mask) {
int cport, cfd, max = MAX_ACCEPTS_PER_CALL;
char cip[NET_IP_STR_LEN];
UNUSED(el);
UNUSED(mask);
UNUSED(privdata);
while(max--) {
cfd = anetTcpAccept(server.neterr, fd, cip, sizeof(cip), &cport);
if (cfd == ANET_ERR) {
if (errno != EWOULDBLOCK)
serverLog(LL_WARNING,
"Accepting client connection: %s", server.neterr);
return;
}
serverLog(LL_VERBOSE,"Accepted %s:%d", cip, cport);
acceptCommonHandler(connCreateAcceptedSocket(cfd),0,cip);
}
}
int anetTcpAccept(char *err, int s, char *ip, size_t ip_len, int *port) {
int fd;
struct sockaddr_storage sa;
socklen_t salen = sizeof(sa);
if ((fd = anetGenericAccept(err,s,(struct sockaddr*)&sa,&salen)) == -1)
return ANET_ERR;
if (sa.ss_family == AF_INET) {
struct sockaddr_in \*s = (struct sockaddr_in *)&sa;
if (ip) inet_ntop(AF_INET,(void*)&(s->sin_addr),ip,ip_len);
if (port) \*port = ntohs(s->sin_port);
} else {
struct sockaddr_in6 \*s = (struct sockaddr_in6 \*)&sa;
if (ip) inet_ntop(AF_INET6,(void*)&(s->sin6_addr),ip,ip_len);
if (port) \*port = ntohs(s->sin6_port);
}
return fd;
}
static void acceptCommonHandler(connection *conn, int flags, char *ip) {
client \*c;
UNUSED(ip);
if (listLength(server.clients) >= server.maxclients) {
char \*err = "-ERR max number of clients reached\r\n";
if (connWrite(conn,err,strlen(err)) == -1) {
}
server.stat_rejected_conn++;
connClose(conn);
return;
}
if ((c = createClient(conn)) == NULL) {
char conninfo[100];
serverLog(LL_WARNING,
"Error registering fd event for the new client: %s (conn: %s)",
connGetLastError(conn),
connGetInfo(conn, conninfo, sizeof(conninfo)));
connClose(conn);
return;
}
c->flags |= flags;
if (connAccept(conn, clientAcceptHandler) == C_ERR) {
char conninfo[100];
serverLog(LL_WARNING,
"Error accepting a client connection: %s (conn: %s)",
connGetLastError(conn), connGetInfo(conn, conninfo, sizeof(conninfo)));
freeClient(connGetPrivateData(conn));
return;
}
}
需要注意的使用aeCreateFileEvent可以注册相关的事件处理方式，比如TLS，PIPE等。在initServer函数最后，初始化相关的日志和监视器等。
回到主函数，接下来就是相关的一系列的检查和相关用户的加载，数据的加载loadDataFromDisk()，在InitServerLast中创建相关的IO线程并处理内存大小。如果是哨兵模式则启动它。最后是最关键的几个函数启动：
aeSetBeforeSleepProc(server.el,beforeSleep);
aeSetAfterSleepProc(server.el,afterSleep);
aeMain(server.el);
aeDeleteEventLoop(server.el);
也就是说，又启动了一个网络的Main函数：
void aeMain(aeEventLoop *eventLoop) {
eventLoop->stop = 0;
while (!eventLoop->stop) {
if (eventLoop->beforesleep != NULL)
eventLoop->beforesleep(eventLoop);
aeProcessEvents(eventLoop, AE_ALL_EVENTS|AE_CALL_AFTER_SLEEP);
}
}
int aeProcessEvents(aeEventLoop *eventLoop, int flags)
{
int processed = 0, numevents;
if (!(flags & AE_TIME_EVENTS) && !(flags & AE_FILE_EVENTS)) return 0;
if (eventLoop->maxfd != -1 ||
((flags & AE_TIME_EVENTS) && !(flags & AE_DONT_WAIT))) {
int j;
aeTimeEvent \*shortest = NULL;
struct timeval tv, \*tvp;
if (flags & AE_TIME_EVENTS && !(flags & AE_DONT_WAIT))
shortest = aeSearchNearestTimer(eventLoop);
if (shortest) {
long now_sec, now_ms;
aeGetTime(&now_sec, &now_ms);
tvp = &tv;
long long ms =
(shortest->when_sec - now_sec)\*1000 +
shortest->when_ms - now_ms;
if (ms > 0) {
tvp->tv_sec = ms/1000;
tvp->tv_usec = (ms % 1000)\*1000;
} else {
tvp->tv_sec = 0;
tvp->tv_usec = 0;
}
} else {
if (flags & AE_DONT_WAIT) {
tv.tv_sec = tv.tv_usec = 0;
tvp = &tv;
} else {
tvp = NULL;
}
}
if (eventLoop->flags & AE_DONT_WAIT) {
tv.tv_sec = tv.tv_usec = 0;
tvp = &tv;
}
numevents = aeApiPoll(eventLoop, tvp);
if (eventLoop->aftersleep != NULL && flags & AE_CALL_AFTER_SLEEP)
eventLoop->aftersleep(eventLoop);
for (j = 0; j < numevents; j++) {
aeFileEvent \*fe = &eventLoop->events[eventLoop->fired[j].fd];
int mask = eventLoop->fired[j].mask;
int fd = eventLoop->fired[j].fd;
int fired = 0;
int invert = fe->mask & AE_BARRIER;
if (!invert && fe->mask & mask & AE_READABLE) {
fe->rfileProc(eventLoop,fd,fe->clientData,mask);
fired++;
}
if (fe->mask & mask & AE_WRITABLE) {
if (!fired || fe->wfileProc != fe->rfileProc) {
fe->wfileProc(eventLoop,fd,fe->clientData,mask);
fired++;
}
}
if (invert && fe->mask & mask & AE_READABLE) {
if (!fired || fe->wfileProc != fe->rfileProc) {
fe->rfileProc(eventLoop,fd,fe->clientData,mask);
fired++;
}
}
processed++;
}
}
if (flags & AE_TIME_EVENTS)
processed += processTimeEvents(eventLoop);
return processed;
}
这玩意儿是不是像Windows窗口里的消息循环的代码。在下面的事件处理函数中，分别处理不同的事件。处理事件的是一个函数指针，在外面初始化好。再看一下beforeSleep和afterSleep两个函数：
void beforeSleep(struct aeEventLoop *eventLoop) {
UNUSED(eventLoop);
// Handle TLS pending data. (must be done before flushAppendOnlyFile)
tlsProcessPendingData();
// If tls still has pending unread data don't sleep at all.
aeSetDontWait(server.el, tlsHasPendingData());
if (server.cluster_enabled) clusterBeforeSleep();
if (server.active_expire_enabled && server.masterhost == NULL)
activeExpireCycle(ACTIVE_EXPIRE_CYCLE_FAST);
if (server.get_ack_from_slaves) {
robj *argv[3];
argv[0] = createStringObject("REPLCONF",8);
argv[1] = createStringObject("GETACK",6);
argv[2] = createStringObject("*",1); // Not used argument.
replicationFeedSlaves(server.slaves, server.slaveseldb, argv, 3);
decrRefCount(argv[0]);
decrRefCount(argv[1]);
decrRefCount(argv[2]);
server.get_ack_from_slaves = 0;
}
if (listLength(server.clients_waiting_acks))
processClientsWaitingReplicas();
if (moduleCount()) moduleHandleBlockedClients();
// Try to process pending commands for clients that were just unblocked.
if (listLength(server.unblocked_clients))
processUnblockedClients();
// Write the AOF buffer on disk
flushAppendOnlyFile(0);
// Handle writes with pending output buffers.
handleClientsWithPendingWritesUsingThreads();
// Close clients that need to be closed asynchronous
freeClientsInAsyncFreeQueue();
if (moduleCount()) moduleReleaseGIL();
}
void afterSleep(struct aeEventLoop *eventLoop) {
UNUSED(eventLoop);
if (moduleCount()) moduleAcquireGIL();
handleClientsWithPendingReadsUsingThreads();
}
beforeSleep用来处理非集群模式下的故障处理，处理过期KEY，处理阻塞的客户端并AOF缓冲区到硬盘。而后者在多路复用调用后被立刻调用。在前文的InitServerLast中，会调用initThreadedIO，这个函数会创建相关的读写线程IOThreadMain：
void *IOThreadMain(void *myid) {
......
while(1) {
......
while((ln = listNext(&li))) {
client \*c = listNodeValue(ln);
if (io_threads_op == IO_THREADS_OP_WRITE) {
writeToClient(c,0);
} else if (io_threads_op == IO_THREADS_OP_READ) {
readQueryFromClient(c->conn);
} else {
serverPanic("io_threads_op value is unknown");
}
}
listEmpty(io_threads_list[id]);
io_threads_pending[id] = 0;
if (tio_debug) printf("[%ld] Done\n", id);
}
}
void readQueryFromClient(connection *conn) {
client \*c = connGetPrivateData(conn);
int nread, readlen;
size_t qblen;
if (postponeClientRead(c)) return;
readlen = PROTO_IOBUF_LEN;
if (c->reqtype == PROTO_REQ_MULTIBULK && c->multibulklen && c->bulklen != -1
&& c->bulklen >= PROTO_MBULK_BIG_ARG)
{
ssize_t remaining = (size_t)(c->bulklen+2)-sdslen(c->querybuf);
if (remaining > 0 && remaining < readlen) readlen = remaining;
}
qblen = sdslen(c->querybuf);
if (c->querybuf_peak < qblen) c->querybuf_peak = qblen;
c->querybuf = sdsMakeRoomFor(c->querybuf, readlen);
nread = connRead(c->conn, c->querybuf+qblen, readlen);
if (nread == -1) {
if (connGetState(conn) == CONN_STATE_CONNECTED) {
return;
} else {
serverLog(LL_VERBOSE, "Reading from client: %s",connGetLastError(c->conn));
freeClientAsync(c);
return;
}
} else if (nread == 0) {
serverLog(LL_VERBOSE, "Client closed connection");
freeClientAsync(c);
return;
} else if (c->flags & CLIENT_MASTER) {
c->pending_querybuf = sdscatlen(c->pending_querybuf,
c->querybuf+qblen,nread);
}
sdsIncrLen(c->querybuf,nread);
c->lastinteraction = server.unixtime;
if (c->flags & CLIENT_MASTER) c->read_reploff += nread;
server.stat_net_input_bytes += nread;
if (sdslen(c->querybuf) > server.client_max_querybuf_len) {
sds ci = catClientInfoString(sdsempty(),c), bytes = sdsempty();
bytes = sdscatrepr(bytes,c->querybuf,64);
serverLog(LL_WARNING,"Closing client that reached max query buffer length: %s (qbuf initial bytes: %s)", ci, bytes);
sdsfree(ci);
sdsfree(bytes);
freeClientAsync(c);
return;
}
processInputBufferAndReplicate(c);
}
如果熟悉SOCKET编程的应该就明白了，在readQueryFromClient开启了数据通信的流程。更具体的解析分析部分，此处不再展开，在后面的部分中会逐一分析。回复亦是如此，在Event事件中调用handleClientsWithPendingWrites：
void sendReplyToClient(connection *conn) {
client \*c = connGetPrivateData(conn);
writeToClient(c,1);
}
通过上述客户端和服务端的连接和通信，一个完整的通信链路就建立了起来。整体的redis的流程也跑了起来。
三、技术优势
在开源的技术框架里，redis的源码算是相当清爽的。简单明了，这就是redis的优势。这在其内部也是如此，数据结构，通信方式等等。简单意味着易维护和应用，明了意味着易于学习和二次开发。实际上，redis的应用也证明了这些。几乎国内所有的大公司的缓存都可以找到redis的身影。
