CODEWITHSUNDEEP
redis
赵文强
赵文强

Reputation: 9

redis used_memory is largger than used_memory_rss

Redis Master has about 90 keys.The longgest key is about 46 bytes.But the master had a 3GB memory usage.Here is the master info information

# Server
redis_version:3.2.8
redis_git_sha1:00000000
redis_git_dirty:0
redis_build_id:b45e9949f92f30de
redis_mode:standalone
os:Linux 3.10.0-327.36.2.el7.ppc64 ppc64
arch_bits:64
multiplexing_api:epoll
gcc_version:4.8.5
process_id:150358
run_id:acfc6247d94cf0c62a98694adf35e3ff9f1c0d9d
tcp_port:6379
uptime_in_seconds:3539
uptime_in_days:0
hz:10
lru_clock:14518804
executable:/home/redis/redis-3.2.8/config/redis-server
config_file:/home/redis/redis-3.2.8/config/server_6379.conf

# Clients
connected_clients:37
client_longest_output_list:0
client_biggest_input_buf:0
blocked_clients:0

# Memory
used_memory:3223126336
used_memory_human:3.00G
used_memory_rss:19988480
used_memory_rss_human:19.06M
used_memory_peak:3223657672
used_memory_peak_human:3.00G
total_system_memory:1071411167232
total_system_memory_human:997.83G
used_memory_lua:37888
used_memory_lua_human:37.00K
maxmemory:0
maxmemory_human:0B
maxmemory_policy:noeviction
mem_fragmentation_ratio:0.01
mem_allocator:jemalloc-4.0.3

# Persistence
loading:0
rdb_changes_since_last_save:143046
rdb_bgsave_in_progress:0
rdb_last_save_time:1776122944
rdb_last_bgsave_status:ok
rdb_last_bgsave_time_sec:-1
rdb_current_bgsave_time_sec:-1
aof_enabled:1
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
aof_current_size:9266469
aof_base_size:0
aof_pending_rewrite:0
aof_buffer_length:0
aof_rewrite_buffer_length:0
aof_pending_bio_fsync:0
aof_delayed_fsync:0

# Stats
total_connections_received:78
total_commands_processed:309390
instantaneous_ops_per_sec:126
total_net_input_bytes:21927610
total_net_output_bytes:62716490
instantaneous_input_kbps:8.79
instantaneous_output_kbps:12.20
rejected_connections:0
sync_full:2
sync_partial_ok:0
sync_partial_err:0
expired_keys:0
evicted_keys:0
keyspace_hits:47603
keyspace_misses:47731
pubsub_channels:1
pubsub_patterns:0
latest_fork_usec:206
migrate_cached_sockets:0

# Replication
role:master
connected_slaves:2
slave0:ip=10.124.152.8,port=6379,state=online,offset=9995541,lag=1
slave1:ip=10.124.152.7,port=6379,state=online,offset=9997441,lag=1
master_repl_offset:9998557
repl_backlog_active:1
repl_backlog_size:3221225472
repl_backlog_first_byte_offset:2
repl_backlog_histlen:9998556

# CPU
used_cpu_sys:7.61
used_cpu_user:3.37
used_cpu_sys_children:0.00
used_cpu_user_children:0.00

# Cluster
cluster_enabled:0

# Keyspace
db0:keys=90,expires=0,avg_ttl=0
And the slave info information

# Memory
used_memory:761448
used_memory_human:743.60K
used_memory_rss:7536640
used_memory_rss_human:7.19M
used_memory_peak:823488
used_memory_peak_human:804.19K
total_system_memory:1071411167232
total_system_memory_human:997.83G
used_memory_lua:37888
used_memory_lua_human:37.00K
maxmemory:0
maxmemory_human:0B
maxmemory_policy:noeviction
mem_fragmentation_ratio:9.90
mem_allocator:jemalloc-4.0.3
127.0.0.1:6379> info
# Server
redis_version:3.2.8
redis_git_sha1:00000000
redis_git_dirty:0
redis_build_id:17a905ed68c0b83
redis_mode:standalone
os:Linux 3.10.0-327.36.2.el7.ppc64 ppc64
arch_bits:64
multiplexing_api:epoll
gcc_version:4.8.5
process_id:151704
run_id:2df76a29acc2910fff7e1ea77203caf0758b23dd
tcp_port:6379
uptime_in_seconds:3673
uptime_in_days:0
hz:10
lru_clock:14518975
executable:/home/redis/redis-3.2.8/config/redis-server
config_file:/home/redis/redis-3.2.8/config/server_6379.conf

# Clients
connected_clients:8
client_longest_output_list:0
client_biggest_input_buf:0
blocked_clients:0

# Memory
used_memory:803360
used_memory_human:784.53K
used_memory_rss:7536640
used_memory_rss_human:7.19M
used_memory_peak:844336
used_memory_peak_human:824.55K
total_system_memory:1071411167232
total_system_memory_human:997.83G
used_memory_lua:37888
used_memory_lua_human:37.00K
maxmemory:0
maxmemory_human:0B
maxmemory_policy:noeviction
mem_fragmentation_ratio:9.38
mem_allocator:jemalloc-4.0.3

# Persistence
loading:0
rdb_changes_since_last_save:150387
rdb_bgsave_in_progress:0
rdb_last_save_time:1776122982
rdb_last_bgsave_status:ok
rdb_last_bgsave_time_sec:-1
rdb_current_bgsave_time_sec:-1
aof_enabled:1
aof_rewrite_in_progress:0
aof_rewrite_scheduled:0
aof_last_rewrite_time_sec:0
aof_current_rewrite_time_sec:-1
aof_last_bgrewrite_status:ok
aof_last_write_status:ok
aof_current_size:9743688
aof_base_size:0
aof_pending_rewrite:0
aof_buffer_length:0
aof_rewrite_buffer_length:0
aof_pending_bio_fsync:0
aof_delayed_fsync:0

# Stats
total_connections_received:7
total_commands_processed:173861
instantaneous_ops_per_sec:58
total_net_input_bytes:11409472
total_net_output_bytes:13484792
instantaneous_input_kbps:3.73
instantaneous_output_kbps:6.38
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:1
pubsub_patterns:0
latest_fork_usec:203
migrate_cached_sockets:0

# Replication
role:slave
master_host:10.124.152.9
master_port:6379
master_link_status:up
master_last_io_seconds_ago:0
master_sync_in_progress:0
slave_repl_offset:10502941
slave_priority:100
slave_read_only:1
connected_slaves:0
master_repl_offset:0
repl_backlog_active:0
repl_backlog_size:3221225472
repl_backlog_first_byte_offset:0
repl_backlog_histlen:0

# CPU
used_cpu_sys:4.19
used_cpu_user:1.72
used_cpu_sys_children:0.00
used_cpu_user_children:0.00

# Cluster
cluster_enabled:0

# Keyspace
db0:keys=90,expires=0,avg_ttl=0

What is the cause of this situation?

Upvotes: 1

Views: 5492

Answers (1)

Murphy Ng
Murphy Ng

Reputation: 562

From the redis doc:

Redis will not always free up (return) memory to the OS when keys are removed. This is not something special about Redis, but it is how most malloc() implementations work. For example if you fill an instance with 5GB worth of data, and then remove the equivalent of 2GB of data, the Resident Set Size (also known as the RSS, which is the number of memory pages consumed by the process) will probably still be around 5GB, even if Redis will claim that the user memory is around 3GB. This happens because the underlying allocator can't easily release the memory. For example often most of the removed keys were allocated in the same pages as the other keys that still exist.

  1. used_memory being smaller than used_memory_rss means that memory fragmentation.
  2. used_memory being bigger than used_memory_rss means that your physical RAM has run out and part of your redis data reside in disk swap space.

But, your problem may lie somewhere far beyond our imagination. 90 keys of 46 bytes DEFINITELY won't make used_memory_human:3.00G! What's more strange, Master's info output says itotal_system_memory_human:997.83G, which means your server's total phsical memory is 997.83G!

Upvotes: 4

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