? ? ? ?每當提到延時統計的時候，一定想到的一個名詞就是”性能測試“，沒錯，在Redis的redis_benchmark文件中，的確用到了延遲文件中的相關信息。在Redis中的官方解釋此文件: ~~~ /* The latency monitor allows to easily observe the sources of latency * in a Redis instance using the LATENCY command. Different latency * sources are monitored, like disk I/O, execution of commands, fork * system call, and so forth. * * 延時監聽器可以對Redis中很多簡單的資源進行監聽，比如I/O磁盤操作，執行一些指令， * fork創建子線程操作等的監聽。 * ---------------------------------------------------------------------------- ~~~ 在Redis中的延時操作中，整個過程原理非常簡單，他是針對每種事件維護了一個統計列表，每個列表中包括了了采集的一系列樣本，每個樣本包括，此樣本的創建時間和此樣本的延時時間。event==》對SampleSeriesList 是一個字典的映射關系。下面看看，里面關鍵的采集點，名叫latencySample采集點的結構定義: ~~~ /* Representation of a latency sample: the sampling time and the latency * observed in milliseconds. */ /* 延時樣品例子 */ struct latencySample { //延時Sample創建的時間 int32_t time; /* We don't use time_t to force 4 bytes usage everywhere. */ //延時的具體時間， 單位為毫秒 uint32_t latency; /* Latency in milliseconds. */ }; ~~~ 字典中維護的可不是一個Sample結點，而是一個結點列表結構體: ~~~ /* The latency time series for a given event. */ /* 針對某個事件采集的一系列延時sample */ struct latencyTimeSeries { //下一個延時Sample的下標 int idx; /* Index of the next sample to store. */ //最大的延時 uint32_t max; /* Max latency observed for this event. */ //最近的延時記錄 struct latencySample samples[LATENCY_TS_LEN]; /* Latest history. */ }; ~~~ 在Redis代碼的設計中，因為延時是用來測試和結果分析的，所以，作者還設計了用于后面分析報告中會用到的數據統計結構體； ~~~ /* Latency statistics structure. */ /* 延時sample的數據統計結果結構體 */ struct latencyStats { //絕對最高的延時時間 uint32_t all_time_high; /* Absolute max observed since latest reset. */ //平均Sample延時時間 uint32_t avg; /* Average of current samples. */ //Sample的最小延時時間 uint32_t min; /* Min of current samples. */ //Sample的最大延時時間 uint32_t max; /* Max of current samples. */ //平均相對誤差，與平均延時相比 uint32_t mad; /* Mean absolute deviation. */ //samples的總數 uint32_t samples; /* Number of non-zero samples. */ //最早的延時記錄點的創建時間 time_t period; /* Number of seconds since first event and now. */ }; ~~~ ?意思都非常的直接，那么一個簡單的Sample如何進行事件的檢測呢？ ~~~ /* Start monitoring an event. We just set the current time. */ /* 對某個事件設置監聽，就是設置一下當前的時間 */ #define latencyStartMonitor(var) if (server.latency_monitor_threshold) { \ var = mstime(); \ } else { \ var = 0; \ } /* End monitoring an event, compute the difference with the current time * to check the amount of time elapsed. */ /* 結束監聽，算出過了多少時間 */ #define latencyEndMonitor(var) if (server.latency_monitor_threshold) { \ var = mstime() - var; \ } ~~~ 很簡單，記錄開始時間，記錄結束時間，中間的差值就是延時時間了，如果超出給定的時間范圍，就加入到延時列表中: ~~~ /* Add the sample only if the elapsed time is >= to the configured threshold. */ /* 如果延時時間超出server.latency_monitor_threshold，則將Sample加入延時列表中 */ #define latencyAddSampleIfNeeded(event,var) \ if (server.latency_monitor_threshold && \ (var) >= server.latency_monitor_threshold) \ latencyAddSample((event),(var)); ~~~ 我們重點關注一下，latencyAddSample，就是把采樣結點加入到記錄中，步驟如下: 1.根據傳入的event事件，在server.latency_events找到key為event事件 的val,即一個latencyTimeSeries 2.在這個latencyTimeSeries的struct latencySample samples[LATENCY_TS_LEN]中添加一個新的Sample 實現代碼如下: ~~~ /* Add the specified sample to the specified time series "event". * This function is usually called via latencyAddSampleIfNeeded(), that * is a macro that only adds the sample if the latency is higher than * server.latency_monitor_threshold. */ /* 添加Sample到指定的Event對象的Sample列表中 */ void latencyAddSample(char *event, mstime_t latency) { //找出Event對應的延時Sample記錄結構體 struct latencyTimeSeries *ts = dictFetchValue(server.latency_events,event); time_t now = time(NULL); int prev; /* Create the time series if it does not exist. */ if (ts == NULL) { ts = zmalloc(sizeof(*ts)); ts->idx = 0; ts->max = 0; memset(ts->samples,0,sizeof(ts->samples)); //如果ts為空，重新添加，一個Event，對應一個latencyTimeSeries dictAdd(server.latency_events,zstrdup(event),ts); } /* If the previous sample is in the same second, we update our old sample * if this latency is > of the old one, or just return. */ prev = (ts->idx + LATENCY_TS_LEN - 1) % LATENCY_TS_LEN; if (ts->samples[prev].time == now) { if (latency > ts->samples[prev].latency) ts->samples[prev].latency = latency; return; } //為Sample賦值 ts->samples[ts->idx].time = time(NULL); ts->samples[ts->idx].latency = latency; if (latency > ts->max) ts->max = latency; ts->idx++; if (ts->idx == LATENCY_TS_LEN) ts->idx = 0; } ~~~ 結點都出來之后，當然會進行結構的分析統計了，這時就用到了latencyStats結構體； ~~~ /* Analyze the samples avaialble for a given event and return a structure * populate with different metrics, average, MAD, min, max, and so forth. * Check latency.h definition of struct latenctStat for more info. * If the specified event has no elements the structure is populate with * zero values. */ /* 分析某個時間Event的延時結果，結果信息存入latencyStats結構體中 */ void analyzeLatencyForEvent(char *event, struct latencyStats *ls) { struct latencyTimeSeries *ts = dictFetchValue(server.latency_events,event); int j; uint64_t sum; //初始化延時統計結果結構體的變量 ls->all_time_high = ts ? ts->max : 0; ls->avg = 0; ls->min = 0; ls->max = 0; ls->mad = 0; ls->samples = 0; ls->period = 0; if (!ts) return; /* First pass, populate everything but the MAD. */ sum = 0; for (j = 0; j < LATENCY_TS_LEN; j++) { if (ts->samples[j].time == 0) continue; ls->samples++; if (ls->samples == 1) { ls->min = ls->max = ts->samples[j].latency; } else { //找出延時最大和最小的延時時間 if (ls->min > ts->samples[j].latency) ls->min = ts->samples[j].latency; if (ls->max < ts->samples[j].latency) ls->max = ts->samples[j].latency; } sum += ts->samples[j].latency; /* Track the oldest event time in ls->period. */ if (ls->period == 0 || ts->samples[j].time < ls->period) //最早的延時記錄點的創建時間 ls->period = ts->samples[j].time; } /* So far avg is actually the sum of the latencies, and period is * the oldest event time. We need to make the first an average and * the second a range of seconds. */ if (ls->samples) { ls->avg = sum / ls->samples; ls->period = time(NULL) - ls->period; if (ls->period == 0) ls->period = 1; } /* Second pass, compute MAD. */ //計算平均相對誤差，與平均延時相比 sum = 0; for (j = 0; j < LATENCY_TS_LEN; j++) { int64_t delta; if (ts->samples[j].time == 0) continue; delta = (int64_t)ls->avg - ts->samples[j].latency; if (delta < 0) delta = -delta; sum += delta; } if (ls->samples) ls->mad = sum / ls->samples; } ~~~ 當然還可以利用這些采集的點，畫一個微線圖，更加形象的展示出來: ~~~ #define LATENCY_GRAPH_COLS 80 /* 利用延時的Sample點，畫出對應的微線圖 */ sds latencyCommandGenSparkeline(char *event, struct latencyTimeSeries *ts) { int j; struct sequence *seq = createSparklineSequence(); sds graph = sdsempty(); uint32_t min = 0, max = 0; for (j = 0; j < LATENCY_TS_LEN; j++) { int i = (ts->idx + j) % LATENCY_TS_LEN; int elapsed; char *label; char buf[64]; if (ts->samples[i].time == 0) continue; /* Update min and max. */ if (seq->length == 0) { min = max = ts->samples[i].latency; } else { if (ts->samples[i].latency > max) max = ts->samples[i].latency; if (ts->samples[i].latency < min) min = ts->samples[i].latency; } /* Use as label the number of seconds / minutes / hours / days * ago the event happened. */ elapsed = time(NULL) - ts->samples[i].time; if (elapsed < 60) snprintf(buf,sizeof(buf),"%ds",elapsed); else if (elapsed < 3600) snprintf(buf,sizeof(buf),"%dm",elapsed/60); else if (elapsed < 3600*24) snprintf(buf,sizeof(buf),"%dh",elapsed/3600); else snprintf(buf,sizeof(buf),"%dd",elapsed/(3600*24)); label = zstrdup(buf); sparklineSequenceAddSample(seq,ts->samples[i].latency,label); } graph = sdscatprintf(graph, "%s - high %lu ms, low %lu ms (all time high %lu ms)\n", event, (unsigned long) max, (unsigned long) min, (unsigned long) ts->max); for (j = 0; j < LATENCY_GRAPH_COLS; j++) graph = sdscatlen(graph,"-",1); graph = sdscatlen(graph,"\n",1); //調用sparkline函數畫微線圖 graph = sparklineRender(graph,seq,LATENCY_GRAPH_COLS,4,SPARKLINE_FILL); freeSparklineSequence(seq); //返回微線圖字符串 return graph; } ~~~ 在Redis還封裝了一些命令供外部調用，這里就不分析了，就是對上述方法的復合調用: ~~~ /* ---------------------------- Latency API --------------------------------- */ void latencyMonitorInit(void) /* 延時監聽初始化操作，創建Event字典對象 */ void latencyAddSample(char *event, mstime_t latency) /* 添加Sample到指定的Event對象的Sample列表中 */ int latencyResetEvent(char *event_to_reset) /* 重置Event事件的延遲，刪除字典中的event的記錄 */ void analyzeLatencyForEvent(char *event, struct latencyStats *ls) /* 分析某個時間Event的延時結果，結果信息存入latencyStats結構體中 */ sds createLatencyReport(void) /* 根據延時Sample的結果，創建閱讀性比較好的分析報告 */ void latencyCommandReplyWithSamples(redisClient *c, struct latencyTimeSeries *ts) void latencyCommandReplyWithLatestEvents(redisClient *c) sds latencyCommandGenSparkeline(char *event, struct latencyTimeSeries *ts) void latencyCommand(redisClient *c) ~~~ Redis的延時類文件的分析也結束了，分析了這么長時間Redis的Redis代碼，感覺每一塊的代碼都會有他的亮點存在，分析了30多期下來，還是學到了很多網上所學不到的知識，網上更多的是Redis主流思想的學習，像一些比較細小點，也只有自己品味，自己才能夠真正的體會。