Redis Slowlog
Source：http://blog.wjin.org/posts/redis-slowlog.html
Declaration: this work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.
Introduction
Slowlog, as its name, is used to record commands whose execution time exceeds limitation (a little slow). It is useful to optimize server performance.
There are two config options for this feature: slowlog-log-slower-than and slowlog-max-len.
slowlog-log-slower-than: time limitation
slowlog-max-len: maximum log entry
Implementation
Data Structure
File: slowlog.h and slowlog.c.
typedef struct slowlogEntry {
robj **argv;
int argc;
long long id; /* Unique entry identifier. */
long long duration; /* Time spent by the query, in nanoseconds. */
time_t time; /* Unix time at which the query was executed. */
} slowlogEntry;
All entries are stored in a single list and each entry has an unique ID.
struct redisServer {
...
list *slowlog; /* SLOWLOG list of commands */
long long slowlog_entry_id; /* SLOWLOG current entry ID */
long long slowlog_log_slower_than; /* SLOWLOG time limit (to get logged) */
unsigned long slowlog_max_len; /* SLOWLOG max number of items logged */
...
};
Init
When redis server starts up, it will call initServer function, this function will call slowlogInit to initialize slowlog related properties.
It also registers a callback slowlogFreeEntry to release slowlog entry.
void slowlogInit(void) {
server.slowlog = listCreate();
server.slowlog_entry_id = 0; // id start from 0
listSetFreeMethod(server.slowlog,slowlogFreeEntry); // free entry callback
}
Add Entry
Inserts new node to list head and delete old node when exceeding max length. slowlogCreateEntry will increate object reference normally.
However it will also create new object sometimes to save memory:
-
string is too long
-
two many arguments, using the last argument to identify more arguments
This is feasible because it is just a log infomation.
void slowlogPushEntryIfNeeded(robj **argv, int argc, long long duration) {
if (server.slowlog_log_slower_than < 0) return; /* Slowlog disabled */
if (duration >= server.slowlog_log_slower_than)
listAddNodeHead(server.slowlog,slowlogCreateEntry(argv,argc,duration));
/* Remove old entries if needed. */
while (listLength(server.slowlog) > server.slowlog_max_len)
listDelNode(server.slowlog,listLast(server.slowlog));
}
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++) {
/* increase obj reference or create new object */
....
}
se->time = time(NULL);
se->duration = duration;
se->id = server.slowlog_entry_id++;
return se;
}
Related Commands
Three sub commands have been given so far: reset, len and get.
void slowlogCommand(redisClient *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"))
{
/* generate each entry info and return it to client */
...
} else {
addReplyError(c,
"Unknown SLOWLOG subcommand or wrong # of args. Try GET, RESET, LEN.");
}
}
Example
Weis-MacBook-Pro:redis eric$ redis-cli
127.0.0.1:6379> config set slowlog-log-slower-than 0
OK
127.0.0.1:6379> config set slowlog-max-len 5
OK
127.0.0.1:6379> set msg "hello, world"
OK
127.0.0.1:6379> set idx 1
OK
127.0.0.1:6379> set x y
OK
127.0.0.1:6379> slowlog get
1) 1) (integer) 4
2) (integer) 1411105058
3) (integer) 8
4) 1) "set"
2) "x"
3) "y"
2) 1) (integer) 3
2) (integer) 1411105037
3) (integer) 11
4) 1) "set"
2) "idx"
3) "1"
3) 1) (integer) 2
2) (integer) 1411105027
3) (integer) 30
4) 1) "set"
2) "msg"
3) "hello, world"
4) 1) (integer) 1
2) (integer) 1411105016
3) (integer) 9
4) 1) "config"
2) "set"
3) "slowlog-max-len"
4) "5"
5) 1) (integer) 0
2) (integer) 1411104979
3) (integer) 26
4) 1) "config"
2) "set"
3) "slowlog-log-slower-than"
4) "0"
127.0.0.1:6379> slowlog get
1) 1) (integer) 5
2) (integer) 1411105073
3) (integer) 31
4) 1) "slowlog"
2) "get"
2) 1) (integer) 4
2) (integer) 1411105058
3) (integer) 8
4) 1) "set"
2) "x"
3) "y"
3) 1) (integer) 3
2) (integer) 1411105037
3) (integer) 11
4) 1) "set"
2) "idx"
3) "1"
4) 1) (integer) 2
2) (integer) 1411105027
3) (integer) 30
4) 1) "set"
2) "msg"
3) "hello, world"
5) 1) (integer) 1
2) (integer) 1411105016
3) (integer) 9
4) 1) "config"
2) "set"
3) "slowlog-max-len"
4) "5"
127.0.0.1:6379>