latency.c

/* 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 -------------------- */

/* latencyCommand() helper to produce a time-delay reply for all the samples
 * in memory for the specified time series. */
void latencyCommandReplyWithSamples(redisClient *c, struct latencyTimeSeries *ts) {
    void *replylen = addDeferredMultiBulkLength(c);
    int samples = 0, j;

    for (j = 0; j < LATENCY_TS_LEN; j++) {
        int i = (ts->idx + j) % LATENCY_TS_LEN;

        if (ts->samples[i].time == 0) continue;
        addReplyMultiBulkLen(c,2);
        addReplyLongLong(c,ts->samples[i].time);
        addReplyLongLong(c,ts->samples[i].latency);
        samples++;
    }
    setDeferredMultiBulkLength(c,replylen,samples);
}

/* LATENCY command implementations.
 *
 * LATENCY SAMPLES: return time-latency samples for the specified event.
 * LATENCY LATEST: return the latest latency for all the events classes.
 * LATENCY DOCTOR: returns an human readable analysis of instance latency.
 * LATENCY GRAPH: provide an ASCII graph of the latency of the specified event.
 */
void latencyCommand(redisClient *c) {
    struct latencyTimeSeries *ts;

    if (!strcasecmp(c->argv[1]->ptr,"samples") && c->argc == 3) {
        /* LATENCY SAMPLES <event> */
        ts = dictFetchValue(server.latency_events,c->argv[2]->ptr);
        if (ts == NULL) goto nodataerr;
        latencyCommandReplyWithSamples(c,ts);
    } else {
        addReply(c,shared.syntaxerr);
        return;
    }
    return;

nodataerr:
    /* Common error when the user asks for an event we have no latency
     * information about. */
    addReplyErrorFormat(c,
        "No samples available for event '%s'", c->argv[2]->ptr);
}