1、 redis命令解析方式分析
在（15）中分析了redis接收命令的方式，它本质是一个使用socket建立的tcp服务器，当有客户端连接到服务器时，他会从连接中读取客户端发送的数据并执行。我们在（15）中分析到了服务器读取出数据后会执行一个processCommand方法来执行命令，这个方法实现在server.c文件中，其内容如下：
int processCommand(client *c) {
moduleCallCommandFilters(c);
/* The QUIT command is handled separately. Normal command procs will
* go through checking for replication and QUIT will cause trouble
* when FORCE_REPLICATION is enabled and would be implemented in
* a regular command proc. */
if (!strcasecmp(c->argv[0]->ptr,"quit")) {
addReply(c,shared.ok);
c->flags |= CLIENT_CLOSE_AFTER_REPLY;
return C_ERR;
}
/* Now lookup the command and check ASAP about trivial error conditions
* such as wrong arity, bad command name and so forth. */
c->cmd = c->lastcmd = lookupCommand(c->argv[0]->ptr);
if (!c->cmd) {
flagTransaction(c);
sds args = sdsempty();
int i;
for (i=1; i < c->argc && sdslen(args) < 128; i++)
args = sdscatprintf(args, "`%.*s`, ", 128-(int)sdslen(args), (char*)c->argv[i]->ptr);
addReplyErrorFormat(c,"unknown command `%s`, with args beginning with: %s",
(char*)c->argv[0]->ptr, args);
sdsfree(args);
return C_OK;
} else if ((c->cmd->arity > 0 && c->cmd->arity != c->argc) ||
(c->argc < -c->cmd->arity)) {
flagTransaction(c);
addReplyErrorFormat(c,"wrong number of arguments for '%s' command",
c->cmd->name);
return C_OK;
}
/* Check if the user is authenticated */
if (server.requirepass && !c->authenticated && c->cmd->proc != authCommand)
{
flagTransaction(c);
addReply(c,shared.noautherr);
return C_OK;
}
/* If cluster is enabled perform the cluster redirection here.
* However we don't perform the redirection if:
* 1) The sender of this command is our master.
* 2) The command has no key arguments. */
if (server.cluster_enabled &&
!(c->flags & CLIENT_MASTER) &&
!(c->flags & CLIENT_LUA &&
server.lua_caller->flags & CLIENT_MASTER) &&
!(c->cmd->getkeys_proc == NULL && c->cmd->firstkey == 0 &&
c->cmd->proc != execCommand))
{
int hashslot;
int error_code;
clusterNode *n = getNodeByQuery(c,c->cmd,c->argv,c->argc,
&hashslot,&error_code);
if (n == NULL || n != server.cluster->myself) {
if (c->cmd->proc == execCommand) {
discardTransaction(c);
} else {
flagTransaction(c);
}
clusterRedirectClient(c,n,hashslot,error_code);
return C_OK;
}
}
/* Handle the maxmemory directive.
*
* Note that we do not want to reclaim memory if we are here re-entering
* the event loop since there is a busy Lua script running in timeout
* condition, to avoid mixing the propagation of scripts with the
* propagation of DELs due to eviction. */
if (server.maxmemory && !server.lua_timedout) {
int out_of_memory = freeMemoryIfNeededAndSafe() == C_ERR;
/* freeMemoryIfNeeded may flush slave output buffers. This may result
* into a slave, that may be the active client, to be freed. */
if (server.current_client == NULL) return C_ERR;
/* It was impossible to free enough memory, and the command the client
* is trying to execute is denied during OOM conditions or the client
* is in MULTI/EXEC context? Error. */
if (out_of_memory &&
(c->cmd->flags & CMD_DENYOOM ||
(c->flags & CLIENT_MULTI && c->cmd->proc != execCommand))) {
flagTransaction(c);
addReply(c, shared.oomerr);
return C_OK;
}
}
/* Don't accept write commands if there are problems persisting on disk
* and if this is a master instance. */
int deny_write_type = writeCommandsDeniedByDiskError();
if (deny_write_type != DISK_ERROR_TYPE_NONE &&
server.masterhost == NULL &&
(c->cmd->flags & CMD_WRITE ||
c->cmd->proc == pingCommand))
{
flagTransaction(c);
if (deny_write_type == DISK_ERROR_TYPE_RDB)
addReply(c, shared.bgsaveerr);
else
addReplySds(c,
sdscatprintf(sdsempty(),
"-MISCONF Errors writing to the AOF file: %s\r\n",
strerror(server.aof_last_write_errno)));
return C_OK;
}
/* Don't accept write commands if there are not enough good slaves and
* user configured the min-slaves-to-write option. */
if (server.masterhost == NULL &&
server.repl_min_slaves_to_write &&
server.repl_min_slaves_max_lag &&
c->cmd->flags & CMD_WRITE &&
server.repl_good_slaves_count < server.repl_min_slaves_to_write)
{
flagTransaction(c);
addReply(c, shared.noreplicaserr);
return C_OK;
}
/* Don't accept write commands if this is a read only slave. But
* accept write commands if this is our master. */
if (server.masterhost && server.repl_slave_ro &&
!(c->flags & CLIENT_MASTER) &&
c->cmd->flags & CMD_WRITE)
{
addReply(c, shared.roslaveerr);
return C_OK;
}
/* Only allow SUBSCRIBE and UNSUBSCRIBE in the context of Pub/Sub */
if (c->flags & CLIENT_PUBSUB &&
c->cmd->proc != pingCommand &&
c->cmd->proc != subscribeCommand &&
c->cmd->proc != unsubscribeCommand &&
c->cmd->proc != psubscribeCommand &&
c->cmd->proc != punsubscribeCommand) {
addReplyError(c,"only (P)SUBSCRIBE / (P)UNSUBSCRIBE / PING / QUIT allowed in this context");
return C_OK;
}
/* Only allow commands with flag "t", such as INFO, SLAVEOF and so on,
* when slave-serve-stale-data is no and we are a slave with a broken
* link with master. */
if (server.masterhost && server.repl_state != REPL_STATE_CONNECTED &&
server.repl_serve_stale_data == 0 &&
!(c->cmd->flags & CMD_STALE))
{
flagTransaction(c);
addReply(c, shared.masterdownerr);
return C_OK;
}
/* Loading DB? Return an error if the command has not the
* CMD_LOADING flag. */
if (server.loading && !(c->cmd->flags & CMD_LOADING)) {
addReply(c, shared.loadingerr);
return C_OK;
}
/* Lua script too slow? Only allow a limited number of commands. */
if (server.lua_timedout &&
c->cmd->proc != authCommand &&
c->cmd->proc != replconfCommand &&
!(c->cmd->proc == shutdownCommand &&
c->argc == 2 &&
tolower(((char*)c->argv[1]->ptr)[0]) == 'n') &&
!(c->cmd->proc == scriptCommand &&
c->argc == 2 &&
tolower(((char*)c->argv[1]->ptr)[0]) == 'k'))
{
flagTransaction(c);
addReply(c, shared.slowscripterr);
return C_OK;
}
/* Exec the command */
if (c->flags & CLIENT_MULTI &&
c->cmd->proc != execCommand && c->cmd->proc != discardCommand &&
c->cmd->proc != multiCommand && c->cmd->proc != watchCommand)
{
queueMultiCommand(c);
addReply(c,shared.queued);
} else {
call(c,CMD_CALL_FULL);
c->woff = server.master_repl_offset;
if (listLength(server.ready_keys))
handleClientsBlockedOnKeys();
}
return C_OK;
}这个方法很长，大多都是一些if语句。他们主要是对于一些特殊情况的处理，对于需要正常执行的命令，其执行的方法在189行。这里执行的call方法才是其执行命令的方法，其内容如下：
void call(client *c, int flags) {
long long dirty;
ustime_t start, duration;
int client_old_flags = c->flags;
struct redisCommand *real_cmd = c->cmd;
server.fixed_time_expire++;
/* Sent the command to clients in MONITOR mode, only if the commands are
* not generated from reading an AOF. */
if (listLength(server.monitors) &&
!server.loading &&
!(c->cmd->flags & (CMD_SKIP_MONITOR|CMD_ADMIN)))
{
replicationFeedMonitors(c,server.monitors,c->db->id,c->argv,c->argc);
}
/* Initialization: clear the flags that must be set by the command on
* demand, and initialize the array for additional commands propagation. */
c->flags &= ~(CLIENT_FORCE_AOF|CLIENT_FORCE_REPL|CLIENT_PREVENT_PROP);
redisOpArray prev_also_propagate = server.also_propagate;
redisOpArrayInit(&server.also_propagate);
/* Call the command. */
dirty = server.dirty;
updateCachedTime(0);
start = server.ustime;
c->cmd->proc(c);
duration = ustime()-start;
dirty = server.dirty-dirty;
if (dirty < 0) dirty = 0;
/* When EVAL is called loading the AOF we don't want commands called
* from Lua to go into the slowlog or to populate statistics. */
if (server.loading && c->flags & CLIENT_LUA)
flags &= ~(CMD_CALL_SLOWLOG | CMD_CALL_STATS);
/* If the caller is Lua, we want to force the EVAL caller to propagate
* the script if the command flag or client flag are forcing the
* propagation. */
if (c->flags & CLIENT_LUA && server.lua_caller) {
if (c->flags & CLIENT_FORCE_REPL)
server.lua_caller->flags |= CLIENT_FORCE_REPL;
if (c->flags & CLIENT_FORCE_AOF)
server.lua_caller->flags |= CLIENT_FORCE_AOF;
}
/* Log the command into the Slow log if needed, and populate the
* per-command statistics that we show in INFO commandstats. */
if (flags & CMD_CALL_SLOWLOG && c->cmd->proc != execCommand) {
char *latency_event = (c->cmd->flags & CMD_FAST) ?
"fast-command" : "command";
latencyAddSampleIfNeeded(latency_event,duration/1000);
slowlogPushEntryIfNeeded(c,c->argv,c->argc,duration);
}
if (flags & CMD_CALL_STATS) {
/* use the real command that was executed (cmd and lastamc) may be
* different, in case of MULTI-EXEC or re-written commands such as
* EXPIRE, GEOADD, etc. */
real_cmd->microseconds += duration;
real_cmd->calls++;
}
/* Propagate the command into the AOF and replication link */
if (flags & CMD_CALL_PROPAGATE &&
(c->flags & CLIENT_PREVENT_PROP) != CLIENT_PREVENT_PROP)
{
int propagate_flags = PROPAGATE_NONE;
/* Check if the command operated changes in the data set. If so
* set for replication / AOF propagation. */
if (dirty) propagate_flags |= (PROPAGATE_AOF|PROPAGATE_REPL);
/* If the client forced AOF / replication of the command, set
* the flags regardless of the command effects on the data set. */
if (c->flags & CLIENT_FORCE_REPL) propagate_flags |= PROPAGATE_REPL;
if (c->flags & CLIENT_FORCE_AOF) propagate_flags |= PROPAGATE_AOF;
/* However prevent AOF / replication propagation if the command
* implementations called preventCommandPropagation() or similar,
* or if we don't have the call() flags to do so. */
if (c->flags & CLIENT_PREVENT_REPL_PROP ||
!(flags & CMD_CALL_PROPAGATE_REPL))
propagate_flags &= ~PROPAGATE_REPL;
if (c->flags & CLIENT_PREVENT_AOF_PROP ||
!(flags & CMD_CALL_PROPAGATE_AOF))
propagate_flags &= ~PROPAGATE_AOF;
/* Call propagate() only if at least one of AOF / replication
* propagation is needed. Note that modules commands handle replication
* in an explicit way, so we never replicate them automatically. */
if (propagate_flags != PROPAGATE_NONE && !(c->cmd->flags & CMD_MODULE))
propagate(c->cmd,c->db->id,c->argv,c->argc,propagate_flags);
}
/* Restore the old replication flags, since call() can be executed
* recursively. */
c->flags &= ~(CLIENT_FORCE_AOF|CLIENT_FORCE_REPL|CLIENT_PREVENT_PROP);
c->flags |= client_old_flags &
(CLIENT_FORCE_AOF|CLIENT_FORCE_REPL|CLIENT_PREVENT_PROP);
/* Handle the alsoPropagate() API to handle commands that want to propagate
* multiple separated commands. Note that alsoPropagate() is not affected
* by CLIENT_PREVENT_PROP flag. */
if (server.also_propagate.numops) {
int j;
redisOp *rop;
if (flags & CMD_CALL_PROPAGATE) {
for (j = 0; j < server.also_propagate.numops; j++) {
rop = &server.also_propagate.ops[j];
int target = rop->target;
/* Whatever the command wish is, we honor the call() flags. */
if (!(flags&CMD_CALL_PROPAGATE_AOF)) target &= ~PROPAGATE_AOF;
if (!(flags&CMD_CALL_PROPAGATE_REPL)) target &= ~PROPAGATE_REPL;
if (target)
propagate(rop->cmd,rop->dbid,rop->argv,rop->argc,target);
}
}
redisOpArrayFree(&server.also_propagate);
}
server.also_propagate = prev_also_propagate;
server.fixed_time_expire--;
server.stat_numcommands++;
}这段代码中执行命令的方法在第28行，执行的是 c->cmd->proc©。要理解这段代码，需要了解redis对命令的处理方式，首先我们需要了解一个名为redisCommand的结构，他定义在server.h中，其内容如下：
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, calls;
};其中name是命令的名称，proc是命令要执行的方法。所以call方法中的第28行代码的意思是执行c（客户端连接时创建的client）中的cmd（上述的redisCommand）中的proc方法。
这样我们只需要确定cmd的具体值，就可以找到其需要执行的方法。而对cmd的赋值在前面的processCommand方法的第16行，这里调用了一个lookupCommand方法，它会根据客户端传来的命令的名称，来找到对应的redisCommand结构，其实现如下：
struct redisCommand *lookupCommand(sds name) {
return dictFetchValue(server.commands, name);
}这里我们可以看见，他实际是从一个叫server.commands的参数中查找数据的，而这个参数在redis服务器启动的时候会被初始化，初始化这个参数的方法为initServerConfig，这个方法里和该参数相关的代码如下：
这段代码中最重要的是在第1711行，这里执行了一个populateCommandTable方法将命令加载到server.commands参数中，这个方法的实现方式如下：
/* Populates the Redis Command Table starting from the hard coded list
* we have on top of redis.c file. */
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, retval2;
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);
/* Populate an additional dictionary that will be unaffected
* by rename-command statements in redis.conf. */
retval2 = dictAdd(server.orig_commands, sdsnew(c->name), c);
serverAssert(retval1 == DICT_OK && retval2 == DICT_OK);
}
}注意这个方法中出现了一个参数：redisCommandTable。我们在之前的文档中介绍了在server.c文件中有一个参数记录了redis所有的命令和其需要执行的方法就是这个参数。而这个方法也很简单就是遍历redisCommandTable，将所有的命令添加到server.commands中。
redisCommandTable的创建方式如下：
如上图所示，redisCommandTable是一个redisCommand结构的数组，他记载了redis所有的命令。
redis命令执行总结
首先redis在启动的时候会先从redisCommandTable中将命令加载到server.commands中，然后当客户端连接到服务器，发送命令后，redis会根据传来的命令在server.commands中找到对应的redisCommand结构，然后执行这个结构中的proc方法。
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