Latency monitor: basic samples collection.

src/latency.c

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+/* 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.
+ *
+ * ----------------------------------------------------------------------------
+ *
+ * Copyright (c) 2014, Salvatore Sanfilippo <antirez at gmail dot com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ *   * Redistributions of source code must retain the above copyright notice,
+ *     this list of conditions and the following disclaimer.
+ *   * Redistributions in binary form must reproduce the above copyright
+ *     notice, this list of conditions and the following disclaimer in the
+ *     documentation and/or other materials provided with the distribution.
+ *   * Neither the name of Redis nor the names of its contributors may be used
+ *     to endorse or promote products derived from this software without
+ *     specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "redis.h"
+
+/* Dictionary type for latency events. Key/Val destructors are set to NULL
+ * since we never delete latency time series at runtime. */
+int dictStringKeyCompare(void *privdata, const void *key1, const void *key2) {
+    return strcmp(key1,key2) == 0;
+}
+
+unsigned int dictStringHash(const void *key) {
+    return dictGenHashFunction(key, strlen(key));
+}
+
+dictType latencyTimeSeriesDictType = {
+    dictStringHash,             /* hash function */
+    NULL,                       /* key dup */
+    NULL,                       /* val dup */
+    dictStringKeyCompare,       /* key compare */
+    NULL,                       /* key destructor */
+    NULL                        /* val destructor */
+};
+
+/* ---------------------------- Latency API --------------------------------- */
+
+/* Latency monitor initialization. We just need to create the dictionary
+ * of time series, each time serie is craeted on demand in order to avoid
+ * having a fixed list to maintain. */
+void latencyMonitorInit(void) {
+    server.latency_events = dictCreate(&latencyTimeSeriesDictType,NULL);
+}
+
+/* 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. */
+void latencyAddSample(char *event, mstime_t latency) {
+    struct latencyTimeSeries *ts = dictFetchValue(server.latency_events,event);
+
+    /* 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));
+        dictAdd(server.latency_events,zstrdup(event),ts);
+    }
+
+    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;
+}
+
+/* ---------------------- Latency command implementation -------------------- */
+
+void latencyCommand(redisClient *c) {
+}