发布时间：2023-05-11 11:30
Redis需要设置最大占用内存吗？如果Redis内存使用超出了设置的最大值会怎样？
找到如下段落，设置maxmemory参数，maxmemory是bytes字节类型，注意转换。修改如下所示：
# In short... if you have slaves attached it is suggested that you set a lower # limit for maxmemory so that there is some free RAM on the system for slave # output buffers (but this is not needed if the policy is \'noeviction\'). # # maxmemorymaxmemory 268435456
本机服务器redis配置文件路径：/usr/local/openresty/lualib/redis/redis.conf，由于本机自带内存只有4G，一般推荐Redis设置内存为最大物理内存的四分之三，所以设置3G，换成Byte是3221225472.
[root@VM-8-8-centos ~]# find / -name redis /etc/selinux/targeted/active/modules/100/redis /usr/local/openresty/lualib/redis
如果Redis的使用超过了设置的最大值会怎样？让我们来改一改上面的配置，故意把最大值设为1个byte试试。
# output buffers (but this is not needed if the policy is \'noeviction\'). # # maxmemorymaxmemory 1
打开debug模式下的页面，提示错误：OOM command not allowed when used memory > ‘maxmemory’.
设置了maxmemory的选项，redis内存使用达到上限。可以通过设置LRU算法来删除部分key，释放空间。默认是按照过期时间的,如果set时候没有加上过期时间就会导致数据写满maxmemory。
如果不设置maxmemory或者设置为0，64位系统不限制内存，32位系统最多使用3GB内存。
LRU是Least Recently Used 最近最少使用算法。
# volatile-lru -> remove the key with an expire set using an LRU algorithm # allkeys-lru -> remove any key accordingly to the LRU algorithm # volatile-random -> remove a random key with 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 expire at all, just return an error on write operations
那么打开配置文件，添加如下一行，使用volatile-lru的过期策略：
maxmemory-policy volatile-lru
保存文件退出，重启redis服务。
如服务器Redis所在目录：/usr/local/openresty/lualib/redis/src
在终端输入./redis-cli，打开Redis客户端，输入info命令。
出来如下信息：
[root@iZ94r80gdghZ src]# ./redis-cli 127.0.0.1:6379> info # Server redis_version:3.0.7 redis_git_sha1:00000000 redis_git_dirty:0 redis_build_id:f07a42660a61a05e redis_mode:standalone os:Linux 3.10.0-327.10.1.el7.x86_64 x86_64 arch_bits:64 multiplexing_api:epoll gcc_version:4.8.5 process_id:2165 run_id:8ec8a8dc969d6e2f2867d9188ccb90850bfc9acb tcp_port:6379 uptime_in_seconds:668 uptime_in_days:0 hz:10 lru_clock:15882419 config_file:/etc/redis/6379.conf # Clients connected_clients:1 client_longest_output_list:0 client_biggest_input_buf:0 blocked_clients:0 # Memory used_memory:816232 used_memory_human:797.10K used_memory_rss:7655424 used_memory_peak:816232 used_memory_peak_human:797.10K used_memory_lua:36864 mem_fragmentation_ratio:9.38 mem_allocator:jemalloc-3.6.0 # Persistence loading:0 rdb_changes_since_last_save:0 rdb_bgsave_in_progress:0 rdb_last_save_time:1458722327 rdb_last_bgsave_status:ok rdb_last_bgsave_time_sec:-1 rdb_current_bgsave_time_sec:-1 aof_enabled:0 aof_rewrite_in_progress:0 aof_rewrite_scheduled:0 aof_last_rewrite_time_sec:-1 aof_current_rewrite_time_sec:-1 aof_last_bgrewrite_status:ok aof_last_write_status:ok # Stats total_connections_received:1 total_commands_processed:0 instantaneous_ops_per_sec:0 total_net_input_bytes:14 total_net_output_bytes:0 instantaneous_input_kbps:0.00 instantaneous_output_kbps:0.00 rejected_connections:0 sync_full:0 sync_partial_ok:0 sync_partial_err:0 expired_keys:0 evicted_keys:0 keyspace_hits:0 keyspace_misses:0 pubsub_channels:0 pubsub_patterns:0 latest_fork_usec:0 migrate_cached_sockets:0 # Replication role:master connected_slaves:0 master_repl_offset:0 repl_backlog_active:0 repl_backlog_size:1048576 repl_backlog_first_byte_offset:0 repl_backlog_histlen:0 # CPU used_cpu_sys:0.30 used_cpu_user:0.29 used_cpu_sys_children:0.00 used_cpu_user_children:0.00 # Cluster cluster_enabled:0 # Keyspace db0:keys=1,expires=1,avg_ttl=425280
其中used_memory:816232，仅用了0.7M左右。
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