我试图获取键值或只是一个键的大小或只是redis中的值。
使用debug object key命令返回键值的序列化大小（如果要写入磁盘），而不是它在内存中使用的实际字节数。
这可以通过检查源代码（基于此Redis: Show database size/size for keys）
来确认https://github.com/antirez/redis/blob/4082c38a60eedd524c78ef48c1b241105f4ddc50/src/debug.c#L337-L343
https://github.com/antirez/redis/blob/4082c38a60eedd524c78ef48c1b241105f4ddc50/src/rdb.c#L663-L671
查看源代码：
/* Save a string object as [len][data] on disk. If the object is a string
* representation of an integer value we try to save it in a special form */
ssize_t rdbSaveRawString(rio *rdb, unsigned char *s, size_t len) {
int enclen;
ssize_t n, nwritten = 0;
/* Try integer encoding */
if (len <= 11) {
unsigned char buf[5];
if ((enclen = rdbTryIntegerEncoding((char*)s,len,buf)) > 0) {
if (rdbWriteRaw(rdb,buf,enclen) == -1) return -1;
return enclen;
}
}
/* Try LZF compression - under 20 bytes it's unable to compress even
* aaaaaaaaaaaaaaaaaa so skip it */
if (server.rdb_compression && len > 20) {
n = rdbSaveLzfStringObject(rdb,s,len);
if (n == -1) return -1;
if (n > 0) return n;
/* Return value of 0 means data can't be compressed, save the old way */
}
/* Store verbatim */
if ((n = rdbSaveLen(rdb,len)) == -1) return -1;
nwritten += n;
if (len > 0) {
if (rdbWriteRaw(rdb,s,len) == -1) return -1;
nwritten += len;
}
return nwritten;
}
通过redis-cli确认：
127.0.0.1:6379> set a aaaaaaaaaaaaaaaaaaa
OK
127.0.0.1:6379> debug object a
Value at:0x7f985822f168 refcount:1 encoding:embstr serializedlength:20 lru:11611136 lru_seconds_idle:2
127.0.0.1:6379> set a aaaaaaaaaaaaaaaaaaaaaaaaaaaaa
OK
127.0.0.1:6379> debug object a
Value at:0x7f985827c428 refcount:1 encoding:embstr serializedlength:12 lru:11611147 lru_seconds_idle:1
所有不同的CLI工具都报告了对象的序列化大小，而不是内存大小，这是有趣且重要的。