redis4.0的命令
简介
目录正文
redisCommand与redisCommandTable
所有的命令一开始都位于server.c文件起始位置的redisCommandTable中，在观察redisCommandTable表之前，我们先看一下redisCommand结构体。
typedef void redisCommandProc(struct client *c);
typedef int *redisGetKeysProc(struct redisCommand *cmd, robj **argv, int argc, int *numkeys);
struct redisCommand {
char *name;
redisCommandProc *proc;
int arity;
char *sflags; /* Flags as string representation, one char per flag. */
int flags; /* The actual flags, obtained from the 'sflags' field. */
/* Use a function to determine keys arguments in a command line.
* Used for Redis Cluster redirect. */
redisGetKeysProc *getkeys_proc;
/* What keys should be loaded in background when calling this command? */
int firstkey; /* The first argument that's a key (0 = no keys) */
int lastkey; /* The last argument that's a key */
int keystep; /* The step between first and last key */
long long microseconds; /* total execution time */
long long calls;/*total execution count */
};
接着我们回到redisCommandTable，此处仅展示其中的get和set命令。
struct redisCommand redisCommandTable[] = {
{"get",getCommand,3,"rF",0,NULL,1,1,1,0,0},
{"set",setCommand,-3,"wm",0,NULL,1,1,1,0,0}
};
name字段为指令的名称，客户端发送请求第一个参数就是指令的名称，name在字典中也被用于key来找到对应的redisCommand。
proc字段为对应的处理函数，在解析完querybuf里的参数后，redis会执行c->cmd->proc(c)调用对应的处理函数，以set指令为例，在这里执行的就是setCommand。下文会对get和set指令做详细的解析。
arity字段遵循以下规则：1. 如果为正，那么指令拥有固定的参数个数。 2.如果为负，那么指令有着最小的参数个数，但参数个数可能会更多。 【参数个数包含指令名称自己】
比如 set指令的最小参数个数为3，set msg "hello" ， 但指令参数可能会更多， SET anotherkey "will expire in a minute" EX 60。
Command arity follows a simple pattern:
- positive if command has fixed number of required arguments.
- negative if command has minimum number of required arguments, but may have more.
Command arity includes counting the command name itself.
sflags和flags代表相同的标志，只是数据的表示形式不同，不同flag代表的意义如下：
- write - command may result in modifications
- readonly - command will never modify keys
- denyoom - reject command if currently out of memory
- admin - server admin command
- pubsub - pubsub-related command
- noscript - deny this command from scripts
- random - command has random results, dangerous for scripts
- sort_for_script - if called from script, sort output
- loading - allow command while database is loading
- stale - allow command while replica has stale data
- skip_monitor - do not show this command in MONITOR
- asking - cluster related - accept even if importing
- fast - command operates in constant or log(N) time. Used for latency monitoring.
- movablekeys - keys have no pre-determined position. You must discover keys yourself.
初始化命令
虽然初始化的工作大多数在redisCommandTable配置中已经完成，但还需要在initserverconfig函数中会调用populateCommandTable将sflags中的字符值转化为flags中的枚举值，并将命令注册到server.commands字典中。
void populateCommandTable(void) {
int j;
int numcommands = sizeof(redisCommandTable)/sizeof(struct redisCommand);
for (j = 0; j < numcommands; j++) {
struct redisCommand *c = redisCommandTable+j;
char *f = c->sflags;
int retval1;
while(*f != '\0') {
switch(*f) {
case 'w': c->flags |= CMD_WRITE; break;
case 'r': c->flags |= CMD_READONLY; break;
case 'm': c->flags |= CMD_DENYOOM; break;
case 'a': c->flags |= CMD_ADMIN; break;
case 'p': c->flags |= CMD_PUBSUB; break;
case 's': c->flags |= CMD_NOSCRIPT; break;
case 'R': c->flags |= CMD_RANDOM; break;
case 'S': c->flags |= CMD_SORT_FOR_SCRIPT; break;
case 'l': c->flags |= CMD_LOADING; break;
case 't': c->flags |= CMD_STALE; break;
case 'M': c->flags |= CMD_SKIP_MONITOR; break;
case 'k': c->flags |= CMD_ASKING; break;
case 'F': c->flags |= CMD_FAST; break;
default: serverPanic("Unsupported command flag"); break;
}
f++;
}
retval1 = dictAdd(server.commands, sdsnew(c->name), c);
serverAssert(retval1 == DICT_OK );
}
}
执行命令
processCommand函数在上篇文章中已经提到过，在解析完querybuf中的字符串，将其转化为client->argc和client->argv中的值后会调用。
processCommand本身做的工作大多数是条件检测，指令是否存在，参数个数是否合法，是否需要验证密码等等。
条件检测通过后，会调用call函数真正调用对应的处理函数。
set指令与字典
如果客户端向服务端发送set msg "hello"请求，在进入到processCommand指令的时候client->argc会被设置为3，client->argv 数组会被填充对应的redisObject 。 lookupCommand会使用client->argv[0]->ptr也就是set去server.commands表中查找对应的redisCommand。
server.commands的类型是dict，在服务器启动时初始化。
typedef struct dict {
dictType *type;
void *privdata;
dictht ht[2];
long rehashidx; /* rehashing not in progress if rehashidx == -1 */
unsigned long iterators; /* number of iterators currently running */
} dict;
创建一个dict对象时会传入对应的dictType对象，dictType对象就是存储了几个函数指针的对象，redis通过它实现了多态的效果。
typedef struct dictType {
uint64_t (*hashFunction)(const void *key);
void *(*keyDup)(void *privdata, const void *key);
void *(*valDup)(void *privdata, const void *obj);
int (*keyCompare)(void *privdata, const void *key1, const void *key2);
void (*keyDestructor)(void *privdata, void *key);
void (*valDestructor)(void *privdata, void *obj);
} dictType;
当创建command表时，使用的是commandTableDictType，这意味着当对一个key哈希的时候，使用的是dictSdsCaseHash将会无视大小写，比较key值使用的函数是dictSdsKeyCaseCompre。