Redis Memory Usage Explanation

Redis real-used memory = process self memory + object memory + buffer memory + fragmentation memory

object memory

sizeof(keys) + sizeof(values)

buffer memory

buffer memory includes client buffer, repl buffer and AOF buffer

client buffer

//普通客户端
client-output-buffer-limit normal 0 0 0
//从客户端 (如果60秒内缓冲区消耗持续大于64MB或者直接超过256MB时)
client-output-buffer-limit replica 256mb 64mb 60
client-output-buffer-limit slave 4096mb 4096mb 1800
//订阅客户端
client-output-buffer-limit pubsub 32mb 8mb 60

repl buffer

复制积压缓冲区，由repl-backlog-size 参数控制，默认1MB

# redis-cli info |grep repl
repl_backlog_active:1                   // 开启复制缓冲区
repl_backlog_size:1048576               // 缓冲区最大长度
repl_backlog_first_byte_offset:7479     // 起始偏移量，计算当前缓冲区可用范围
repl_backlog_histlen:1048576            // 已保存数据的有效长度

AOF buffer

will buffer writting commands during aofwrite, controlled by Redis

fragmentation memory

controlled by redis process, append, setrange, expire and del etc. commands will increase the mem_fragmentation_ratio

# redis-cli info |grep frag
allocator_frag_ratio:1.20
allocator_frag_bytes:290200
mem_fragmentation_ratio:18.78
mem_fragmentation_bytes:14394880
active_defrag_running:0
active_defrag_hits:0
active_defrag_misses:0
active_defrag_key_hits:0
active_defrag_key_misses:0

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