【面試題】一文講清，為啥redis單線程還有很高的性能？

#define MAX_ACCEPTS_PER_CALL 1000void 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);　　//循環(huán)處理連接應(yīng)答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);    }}

void readQueryFromClient(aeEventLoop *el, int fd, void *privdata, int mask) {    client *c = (client*) privdata;    int nread, readlen;    size_t qblen;UNUSED(el);UNUSED(mask);
    readlen = PROTO_IOBUF_LEN;/* If this is a multi bulk request, and we are processing a bulk reply     * that is large enough, try to maximize the probability that the query     * buffer contains exactly the SDS string representing the object, even     * at the risk of requiring more read(2) calls. This way the function     * processMultiBulkBuffer() can avoid copying buffers to create the     * Redis Object representing the argument. */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);
/* Note that the 'remaining' variable may be zero in some edge case,         * for example once we resume a blocked client after CLIENT PAUSE. */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 = read(fd, c->querybuf+qblen, readlen);if (nread == -1) {if (errno == EAGAIN) {return;        } else {            serverLog(LL_VERBOSE, "Reading from client: %s",strerror(errno));            freeClient(c);return;        }    } else if (nread == 0) {        serverLog(LL_VERBOSE, "Client closed connection");        freeClient(c);return;    } else if (c->flags & CLIENT_MASTER) {/* Append the query buffer to the pending (not applied) buffer         * of the master. We'll use this buffer later in order to have a         * copy of the string applied by the last command executed. */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);        freeClient(c);return;    }
/* Time to process the buffer. If the client is a master we need to     * compute the difference between the applied offset before and after     * processing the buffer, to understand how much of the replication stream     * was actually applied to the master state: this quantity, and its     * corresponding part of the replication stream, will be propagated to     * the sub-slaves and to the replication backlog. */    processInputBufferAndReplicate(c);}
void processInputBufferAndReplicate(client *c) {if (!(c->flags & CLIENT_MASTER)) {        processInputBuffer(c);    } else {        size_t prev_offset = c->reploff;        processInputBuffer(c);        size_t applied = c->reploff - prev_offset;if (applied) {            replicationFeedSlavesFromMasterStream(server.slaves,c->pending_querybuf, applied);            sdsrange(c->pending_querybuf,applied,-1);        }    }}