从源码分析 Redis 异步删除各个参数的具体作用

// DEL 命令调用的函数
void delCommand(client *c) {
    delGenericCommand(c,server.lazyfree_lazy_user_del);
}

// UNLINK 命令调用的函数
void unlinkCommand(client *c) {
    delGenericCommand(c,1);
}

/* Return the set of flags to use for the emptyDb() call for FLUSHALL
 * and FLUSHDB commands.
 *
 * sync: flushes the database in an sync manner.
 * async: flushes the database in an async manner.
 * no option: determine sync or async according to the value of lazyfree-lazy-user-flush.
 *
 * On success C_OK is returned and the flags are stored in *flags, otherwise
 * C_ERR is returned and the function sends an error to the client. */
int getFlushCommandFlags(client *c, int *flags) {
    /* Parse the optional ASYNC option. */
    if (c->argc == 2 && !strcasecmp(c->argv[1]->ptr,"sync")) {
        *flags = EMPTYDB_NO_FLAGS;
    } else if (c->argc == 2 && !strcasecmp(c->argv[1]->ptr,"async")) {
        *flags = EMPTYDB_ASYNC;
    } else if (c->argc == 1) {
        *flags = server.lazyfree_lazy_user_flush ? EMPTYDB_ASYNC : EMPTYDB_NO_FLAGS;
    } else {
        addReplyErrorObject(c,shared.syntaxerr);
        return C_ERR;
    }
    return C_OK;
}

/* This is a wrapper whose behavior depends on the Redis lazy free
 * configuration. Deletes the key synchronously or asynchronously. */
int dbDelete(redisDb *db, robj *key) {
    return dbGenericDelete(db, key, server.lazyfree_lazy_server_del);
}

/* Overwrite an existing key with a new value. Incrementing the reference
 * count of the new value is up to the caller.
 * This function does not modify the expire time of the existing key.
 *
 * The program is aborted if the key was not already present. */
void dbOverwrite(redisDb *db, robj *key, robj *val) {
    dictEntry *de = dictFind(db->dict,key->ptr);
    ...
    if (server.lazyfree_lazy_server_del) {
        freeObjAsync(key,old,db->id);
        dictSetVal(db->dict, &auxentry, NULL);
    }

    dictFreeVal(db->dict, &auxentry);
}

/* Delete the specified expired key and propagate expire. */
void deleteExpiredKeyAndPropagate(redisDb *db, robj *keyobj) {
    mstime_t expire_latency;
    latencyStartMonitor(expire_latency);
    // 删除过期 KEY
    if (server.lazyfree_lazy_expire)
        dbAsyncDelete(db,keyobj);
    else
        dbSyncDelete(db,keyobj);
    latencyEndMonitor(expire_latency);
    latencyAddSampleIfNeeded("expire-del",expire_latency);
    notifyKeyspaceEvent(NOTIFY_EXPIRED,"expired",keyobj,db->id);
    signalModifiedKey(NULL, db, keyobj);
    // 将删除操作传播给从库及写到 AOF 文件中
    propagateDeletion(db,keyobj,server.lazyfree_lazy_expire);
    server.stat_expiredkeys++;
}

if (iAmMaster() &&
    !(rdbflags & RDBFLAGS_AOF_PREAMBLE) &&
    expiretime != -1 && expiretime < now)
{
    if (rdbflags & RDBFLAGS_FEED_REPL) {
        /* Caller should have created replication backlog,
         * and now this path only works when rebooting,
         * so we don't have replicas yet. */
        serverAssert(server.repl_backlog != NULL && listLength(server.slaves) == 0);
        robj keyobj;
        initStaticStringObject(keyobj, key);
        robj *argv[2];
        argv[0] = server.lazyfree_lazy_expire ? shared.unlink : shared.del;
        argv[1] = &keyobj;
        replicationFeedSlaves(server.slaves, dbid, argv, 2);
    }
    sdsfree(key);
    decrRefCount(val);
    server.rdb_last_load_keys_expired++;
}

/* Finally remove the selected key. */
if (bestkey) {
    db = server.db + bestdbid;
    robj *keyobj = createStringObject(bestkey, sdslen(bestkey));
    delta = (long long) zmalloc_used_memory();
    latencyStartMonitor(eviction_latency);
    // 删除 KEY 
    if (server.lazyfree_lazy_eviction)
        dbAsyncDelete(db, keyobj);
    else
        dbSyncDelete(db, keyobj);
    latencyEndMonitor(eviction_latency);
    latencyAddSampleIfNeeded("eviction-del", eviction_latency);
    delta -= (long long) zmalloc_used_memory();
    mem_freed += delta;
    server.stat_evictedkeys++;
    signalModifiedKey(NULL, db, keyobj);
    notifyKeyspaceEvent(NOTIFY_EVICTED, "evicted", keyobj, db->id);
    // 将删除操作传播给从库并写到 AOF 文件中
    propagateDeletion(db, keyobj, server.lazyfree_lazy_eviction);
    decrRefCount(keyobj);
    keys_freed++;
    ...
}

/* Asynchronously read the SYNC payload we receive from a master */
#define REPL_MAX_WRITTEN_BEFORE_FSYNC (1024*1024*8) /* 8 MB */
void readSyncBulkPayload(connection *conn) {
    char buf[PROTO_IOBUF_LEN];
    ssize_t nread, readlen, nwritten;
    int use_diskless_load = useDisklessLoad();
    redisDb *diskless_load_tempDb = NULL;
    functionsLibCtx* temp_functions_lib_ctx = NULL;
    int empty_db_flags = server.repl_slave_lazy_flush ? EMPTYDB_ASYNC :
                                                        EMPTYDB_NO_FLAGS;
    ...
    if (use_diskless_load && server.repl_diskless_load == REPL_DISKLESS_LOAD_SWAPDB) {
        /* Initialize empty tempDb dictionaries. */
        diskless_load_tempDb = disklessLoadInitTempDb();
        temp_functions_lib_ctx = functionsLibCtxCreate();

        moduleFireServerEvent(REDISMODULE_EVENT_REPL_ASYNC_LOAD,
                              REDISMODULE_SUBEVENT_REPL_ASYNC_LOAD_STARTED,
                              NULL);
    } else {
        replicationAttachToNewMaster();

        serverLog(LL_NOTICE, "MASTER <-> REPLICA sync: Flushing old data");
        emptyData(-1,empty_db_flags,replicationEmptyDbCallback);
    }
    ...
}