结合redis设计与实现的redis源码学习-25-慢查询日志（slowlog）

Redis的慢查询日志功能用于记录执行时间超过给定时长的命令请求，用户可以通过这个功能产生的日志来监控和优化查询速度。
服务器配置有两个和慢查询日志相关的选项：
-1、slowlog-log-slower-than选项指定执行时间超过多少微妙的命令会被记录到日志上。
-2、slowlog-max-len选项指定服务器最多保存多少条慢查询日志。
服务器使用先进先出的方式保存多条慢查询日志，当达到设置的最大值时，服务器在添加一条新的慢查询日志之前，会先将最旧的一条删除。

一、慢查询记录的保存

struct redisServer{    long long slowlog_entry_id;//下一条慢查询日志的ID    list *slowlog;//保存了所有慢查询日志的链表    long long slowlog_log_slower_than;//服务器配置的保存日志的命令执行时间    unsigned long slowlog_max_len;//服务器配置的最大日志长度}

其中链表保存的每个节点都是一个结构体：

typedef struct slowlogEntry{    long long id;//唯一标识符    time_t time；//命令执行的时间    long long duration;//执行命令消耗的时间，以微妙为单位    robj **argv;//命令与参数    int argc;//命令与参数的数量}

二、添加新日志

在每次执行命令之前和之后，程序都会记录微妙格式的当前UNIX时间戳，这两个时间戳之间的差就是服务器执行命令所耗费的时长，服务器会将这个时长作为参数之一传给slowlogPushEntryIfNeeded函数，负责检查是否需要为这次执行的命令创建慢查询日志。

看代码

slowlog.h

#define SLOWLOG_ENTRY_MAX_ARGC 32#define SLOWLOG_ENTRY_MAX_STRING 128/* Exported API 导出的API*/void slowlogInit(void);void slowlogPushEntryIfNeeded(robj **argv, int argc, long long duration);/* Exported commands 导出的命令*/void slowlogCommand(client *c);

slowlog.c

#include "server.h"#include "slowlog.h"/* Create a new slowlog entry.创建一个日志条目 * Incrementing the ref count of all the objects retained is up to this function. 增加保留的所有对象的引用计数器取决于此功能*/slowlogEntry *slowlogCreateEntry(robj **argv, int argc, long long duration) {    slowlogEntry *se = zmalloc(sizeof(*se));    int j, slargc = argc;    if (slargc > SLOWLOG_ENTRY_MAX_ARGC) slargc = SLOWLOG_ENTRY_MAX_ARGC;    se->argc = slargc;    se->argv = zmalloc(sizeof(robj*)*slargc);    for (j = 0; j < slargc; j++) {        /* Logging too many arguments is a useless memory waste, so we stop at SLOWLOG_ENTRY_MAX_ARGC, but use the last argument to specify how many remaining arguments there were in the original command. 记录过多的参数是无用的内存浪费，但是我们使用最后一个参数来指定原始命令中剩余的参数数量*/        if (slargc != argc && j == slargc-1) {            se->argv[j] = createObject(OBJ_STRING,                sdscatprintf(sdsempty(),"... (%d more arguments)",                argc-slargc+1));        } else {            /* Trim too long strings as well... 截取太长的字符串*/            if (argv[j]->type == OBJ_STRING &&                sdsEncodedObject(argv[j]) &&                sdslen(argv[j]->ptr) > SLOWLOG_ENTRY_MAX_STRING)            {                sds s = sdsnewlen(argv[j]->ptr, SLOWLOG_ENTRY_MAX_STRING);                s = sdscatprintf(s,"... (%lu more bytes)",                    (unsigned long)                    sdslen(argv[j]->ptr) - SLOWLOG_ENTRY_MAX_STRING);                se->argv[j] = createObject(OBJ_STRING,s);            } else {                se->argv[j] = argv[j];                incrRefCount(argv[j]);            }        }    }    se->time = time(NULL);    se->duration = duration;    se->id = server.slowlog_entry_id++;    return se;}/* Free a slow log entry. The argument is void so that the prototype of this function matches the one of the 'free' method of adlist.c.释放一个日志条目，这个参数是无效的，所以这个函数的原型与adlist.c的free方法中的一个匹配 This function will take care to release all the retained object. 这个函数小心的释放所有保留的对象*/void slowlogFreeEntry(void *septr) {    slowlogEntry *se = septr;    int j;    for (j = 0; j < se->argc; j++)        decrRefCount(se->argv[j]);    zfree(se->argv);    zfree(se);}/* Initialize the slow log. This function should be called a single time at server startup. 初始化慢查询日志，这个函数只会在服务器启动时调用*/void slowlogInit(void) {    server.slowlog = listCreate();    server.slowlog_entry_id = 0;    listSetFreeMethod(server.slowlog,slowlogFreeEntry);}/* Push a new entry into the slow log.插入一条日志 This function will make sure to trim the slow log accordingly to the configured max length. 这个函数判断是否需要创建日志*/void slowlogPushEntryIfNeeded(robj **argv, int argc, long long duration) {    if (server.slowlog_log_slower_than < 0) return; /* Slowlog disabled 没有开启慢查询日志，直接返回*/    if (duration >= server.slowlog_log_slower_than)        listAddNodeHead(server.slowlog,slowlogCreateEntry(argv,argc,duration));    /* Remove old entries if needed. 如果超过最大长度，删除最旧的*/    while (listLength(server.slowlog) > server.slowlog_max_len)        listDelNode(server.slowlog,listLast(server.slowlog));}/* Remove all the entries from the current slow log. 释放所有日志条目*/void slowlogReset(void) {    while (listLength(server.slowlog) > 0)        listDelNode(server.slowlog,listLast(server.slowlog));}/* The SLOWLOG command. Implements all the subcommands needed to handle the Redis slow log. 执行慢查询日志的相关命令*/void slowlogCommand(client *c) {    if (c->argc == 2 && !strcasecmp(c->argv[1]->ptr,"reset")) {        slowlogReset();        addReply(c,shared.ok);    } else if (c->argc == 2 && !strcasecmp(c->argv[1]->ptr,"len")) {        addReplyLongLong(c,listLength(server.slowlog));    } else if ((c->argc == 2 || c->argc == 3) &&               !strcasecmp(c->argv[1]->ptr,"get"))    {        long count = 10, sent = 0;        listIter li;        void *totentries;        listNode *ln;        slowlogEntry *se;        if (c->argc == 3 &&            getLongFromObjectOrReply(c,c->argv[2],&count,NULL) != C_OK)            return;        listRewind(server.slowlog,&li);        totentries = addDeferredMultiBulkLength(c);        while(count-- && (ln = listNext(&li))) {            int j;            se = ln->value;            addReplyMultiBulkLen(c,4);            addReplyLongLong(c,se->id);            addReplyLongLong(c,se->time);            addReplyLongLong(c,se->duration);            addReplyMultiBulkLen(c,se->argc);            for (j = 0; j < se->argc; j++)                addReplyBulk(c,se->argv[j]);            sent++;        }        setDeferredMultiBulkLength(c,totentries,sent);    } else {        addReplyError(c,            "Unknown SLOWLOG subcommand or wrong # of args. Try GET, RESET, LEN.");    }}