Redis5.0优化-内存使用统计报告优化

Redis5.0优化点中有内存使用统计报告的优化，下面分别在Redis4的版本和Redis5的版本中分别使用info memory命令来查看返回结果，进行对比。

• Redis4.0.14 INFO MEMORY结果

  [root@redis-7-105 conf]# redis-cli -p 7008 info memory
  # Memory
  used_memory:14835120
  used_memory_human:14.15M
  used_memory_rss:24780800
  used_memory_rss_human:23.63M
  used_memory_peak:14884304
  used_memory_peak_human:14.19M
  used_memory_peak_perc:99.67%
  used_memory_overhead:1941912
  used_memory_startup:786640
  used_memory_dataset:12893208
  used_memory_dataset_perc:91.78%
  total_system_memory:1019572224
  total_system_memory_human:972.34M
  used_memory_lua:37888
  used_memory_lua_human:37.00K
  maxmemory:0
  maxmemory_human:0B
  maxmemory_policy:noeviction
  mem_fragmentation_ratio:1.67
  mem_allocator:jemalloc-4.0.3
  active_defrag_running:0
  lazyfree_pending_objects:0
  

• Redis5.0.9 INFO MEMORY结果

  [root@reids-7-104 data]# redis-cli -p 7007 info memory
  # Memory
  used_memory:13771704
  used_memory_human:13.13M
  used_memory_rss:27258880
  used_memory_rss_human:26.00M
  used_memory_peak:13812512
  used_memory_peak_human:13.17M
  used_memory_peak_perc:99.70%
  used_memory_overhead:882422
  used_memory_startup:792456
  used_memory_dataset:12889282
  used_memory_dataset_perc:99.31%
  allocator_allocated:13982280
  allocator_active:15417344
  allocator_resident:24666112
  total_system_memory:1019572224
  total_system_memory_human:972.34M
  used_memory_lua:37888
  used_memory_lua_human:37.00K
  used_memory_scripts:0
  used_memory_scripts_human:0B
  number_of_cached_scripts:0
  maxmemory:0
  maxmemory_human:0B
  maxmemory_policy:noeviction
  allocator_frag_ratio:1.10
  allocator_frag_bytes:1435064
  allocator_rss_ratio:1.60
  allocator_rss_bytes:9248768
  rss_overhead_ratio:1.11
  rss_overhead_bytes:2592768
  mem_fragmentation_ratio:1.99
  mem_fragmentation_bytes:13549080
  mem_not_counted_for_evict:0
  mem_replication_backlog:0
  mem_clients_slaves:0
  mem_clients_normal:49694
  mem_aof_buffer:0
  mem_allocator:jemalloc-5.1.0
  active_defrag_running:0
  lazyfree_pending_objects:0
  

通过在线文本比较工具可以看到，Redis5.0.9的返回结果中，比Redis4.0.14的结果多了一些内存统计信息：

• allocator_frag_ratio: Ratio between allocator_active and allocator_allocated. This is the true (external) fragmentation metric (not mem_fragmentation_ratio).

  allocator_frag_ratio：分配器碎片比率，即分配器活跃的内存占分配器总内存的比例。这是实际的外部碎片指标（非内存碎片率mem_fragmentation_ratio）

• allocator_frag_bytes Delta between allocator_active and allocator_allocated. See note about mem_fragmentation_bytes.

  allocator_frag_bytes：分配器活跃的内存和分配器总内存的差值。

• allocator_rss_ratio: Ratio between allocator_resident and allocator_active. This usually indicates pages that the allocator can and probably will soon release back to the OS.

  allocator_rss_ratio：分配器常驻内存占分配器活跃的内存的比例。这通常表示着分配器将很快释放回到操作系统的内存页。

• allocator_rss_bytes: Delta between allocator_resident and allocator_active

  allocator_rss_bytes：分配器常驻内存和分配器活跃的内存的差值。

• rss_overhead_ratio: Ratio between used_memory_rss (the process RSS) and allocator_resident. This includes RSS overheads that are not allocator or heap related.

  rss_overhead_ratio：进程常驻内存和分配器常驻内存的比率。这包括既非分配器和也非堆的内存开销。

• rss_overhead_bytes: Delta between used_memory_rss (the process RSS) and allocator_resident

  rss_overhead_bytes：进程常驻内存和分配器常驻内存的差值。

• allocator_allocated: Total bytes allocated form the allocator, including internal-fragmentation. Normally the same as used_memory.

  allocator_allocated：分配器总内存，包括内部碎片。通常与used_memory相同。

• mem_not_counted_for_evict: Used memory that’s not counted for key eviction. This is basically transient replica and AOF buffers.

  mem_not_counted_for_evict：除去驱逐key的已用内存。这基本是临时副本和AOF缓冲区。

• mem_clients_slaves: Memory used by replica clients - Starting Redis 7.0, replica buffers share memory with the replication backlog, so this field can show 0 when replicas don’t trigger an increase of memory usage.

  mem_clients_slaves：副本客户端使用的内存，从Redis7.0开始，副本缓冲区与副本回溯缓冲区共享内存，因此当副本不触发内存增长时，这个字段可能显示0。

• mem_clients_normal: Memory used by normal clients

  mem_clients_normal：普通客户端使用的内存。

• mem_aof_buffer: Transient memory used for AOF and AOF rewrite buffers

  mem_aof_buffer：用于AOF和AOF重写缓冲区的临时内存。

• mem_replication_backlog: Memory used by replication backlog

  mem_replication_backlog：用于副本回溯缓冲区的内存。

• mem_fragmentation_bytes: Delta between used_memory_rss and used_memory. Note that when the total fragmentation bytes is low (few megabytes), a high ratio (e.g. 1.5 and above) is not an indication of an issue.

  mem_fragmentation_bytes：分配器常驻内存used_memory_rss和分配器活跃内存used_memory的差值。当总碎片字节数低（几兆字节）但碎片率高（例如1.5以上）的情况不算问题。