# 客户端命令方式配置和查看内存大小
127.0.0.1:6379> config get maxmemory
"maxmemory"
"0"
127.0.0.1:6379> config set maxmemory 100mb
OK
127.0.0.1:6379> config get maxmemory
"maxmemory"
"104857600"
# 配置文件配置maxmemory大小
# WARNING: not setting maxmemory will cause Redis to terminate with an
# out-of-memory exception if the heap limit is reached.
#
# NOTE: since Redis uses the system paging file to allocate the heap memory,
# the Working Set memory usage showed by the Windows Task Manager or by other
# tools such as ProcessExplorer will not always be accurate. For example, right
# after a background save of the RDB or the AOF files, the working set value
# may drop significantly. In order to check the correct amount of memory used
# by the redis-server to store the data, use the INFO client command. The INFO
# command shows only the memory used to store the redis data, not the extra
# memory used by the Windows process for its own requirements. Th3 extra amount
# of memory not reported by the INFO command can be calculated subtracting the
# Peak Working Set reported by the Windows Task Manager and the used_memory_peak
# reported by the INFO command.
#
maxmemory 100mb
#...

#redis.conf文件配置方式
# MAXMEMORY POLICY: how Redis will select what to remove when maxmemory
# is reached. You can select one from the following behaviors:
#
# volatile-lru -> Evict using approximated LRU, only keys with an expire set.
# allkeys-lru -> Evict any key using approximated LRU.
# volatile-lfu -> Evict using approximated LFU, only keys with an expire set.
# allkeys-lfu -> Evict any key using approximated LFU.
# volatile-random -> Remove a random key having an expire set.
# allkeys-random -> Remove a random key, any key.
# volatile-ttl -> Remove the key with the nearest expire time (minor TTL)
# noeviction -> Don't evict anything, just return an error on write operations.
#
# LRU means Least Recently Used
# LFU means Least Frequently Used
#
# Both LRU, LFU and volatile-ttl are implemented using approximated
# randomized algorithms.
# The default is:
# ...
maxmemory-policy noeviction

# 命令行配置方式
127.0.0.1:6379> CONFIG GET maxmemory-policy
"maxmemory-policy"
"noeviction"
127.0.0.1:6379> CONFIG SET maxmemory-policy volatile-lru
OK
127.0.0.1:6379> CONFIG GET maxmemory-policy
"maxmemory-policy"
"volatile-lru"

# expire: t秒后过期
expire key seconds
# pexpire: t毫秒后过期
pexpire key millseconds
# expireat: 到达具体的时间戳时过期,精确到秒
expireat key timestamp
# pexpireat: 到达具体的时间戳时过期，精确到毫秒
pexpire key millseconds

//expire命令
void expireCommand(redisClient *c) {
  expireGenericCommand(c,mstime(),UNIT_SECONDS);
}
//expireat命令
void expireatCommand(redisClient *c) {
  expireGenericCommand(c,0,UNIT_SECONDS);
}
//pexpire命令
void pexpireCommand(redisClient *c) {
  expireGenericCommand(c,mstime(),UNIT_MILLISECONDS);
}
//pexpireat命令
void pexpireatCommand(redisClient *c) {
  expireGenericCommand(c,0,UNIT_MILLISECONDS);
}
/* This is the generic command implementation for EXPIRE, PEXPIRE, EXPIREAT
* and PEXPIREAT. Because the commad second argument may be relative or absolute
* the "basetime" argument is used to signal what the base time is (either 0
* for *AT variants of the command, or the current time for relative expires).
*/
void expireGenericCommand(redisClient *c, long long basetime, int unit) {
  ...
  /* unix time in milliseconds when the key will expire. */
  long long when; 
  ...
  //如果是秒转换为毫秒
  if (unit == UNIT_SECONDS) when *= 1000;
  when += basetime;
  ...
}