Trouble on Redis RAM usage behavior

Redis commands & data structures
1

Hi,

Redis version :5.0.7
Amount of RAM on the server : 15G.
maxmemory-policy : volatile-lru
maxmemory : 6.44G
mem_fragmentation_ratio : 1.14

We have an instance of Redis on our Linux server. This instance of Redis is used on a PHP application. We ‘discover’ that we’ve huge fall of memory usage when the maxmemory amount is hit. This brutal fall affects our db graph. See bellow a graph representing the fall of the memory usage when redis hit max memory usage limit :

image

Is this pattern a ‘normal’ pattern for the given maxmemory policy ?
Furthermore, i’m asking myself if it’s a good practice to restart the redis instances in order to purge the redis cache at specific and controlled time ? For example, every night.

Best regards,

2

Please provide more details about your keyspace (INFO ALL, or INFO MEMORY & INFO STATS & INFO KEYSPACE)

3

INFO MEMORY :

# Memory
used_memory:6442160912
used_memory_human:6.00G
used_memory_rss:7506419712
used_memory_rss_human:6.99G
used_memory_peak:6442619352
used_memory_peak_human:6.00G
used_memory_peak_perc:99.99%
used_memory_overhead:31949160
used_memory_startup:787976
used_memory_dataset:6410211752
used_memory_dataset_perc:99.52%
allocator_allocated:6442375952
allocator_active:7409078272
allocator_resident:7519395840
total_system_memory:16773713920
total_system_memory_human:15.62G
used_memory_lua:41984
used_memory_lua_human:41.00K
used_memory_scripts:0
used_memory_scripts_human:0B
number_of_cached_scripts:0
maxmemory:6442450944
maxmemory_human:6.00G
maxmemory_policy:volatile-lru
allocator_frag_ratio:1.15
allocator_frag_bytes:966702320
allocator_rss_ratio:1.01
allocator_rss_bytes:110317568
rss_overhead_ratio:1.00
rss_overhead_bytes:-12976128
mem_fragmentation_ratio:1.17
mem_fragmentation_bytes:1064342496
mem_not_counted_for_evict:0
mem_replication_backlog:0
mem_clients_slaves:0
mem_clients_normal:3019544
mem_aof_buffer:0
mem_allocator:jemalloc-5.2.1
active_defrag_running:0
lazyfree_pending_objects:0

INFO STATS :

# Stats
total_connections_received:41669227
total_commands_processed:4507027762
instantaneous_ops_per_sec:7987
total_net_input_bytes:864965196534
total_net_output_bytes:66856177812671
instantaneous_input_kbps:1657.71
instantaneous_output_kbps:30558.57
rejected_connections:0
sync_full:0
sync_partial_ok:0
sync_partial_err:0
expired_keys:5913479
expired_stale_perc:0.74
expired_time_cap_reached_count:0
evicted_keys:7839
keyspace_hits:3572609020
keyspace_misses:581662138
pubsub_channels:0
pubsub_patterns:0
latest_fork_usec:0
migrate_cached_sockets:0
slave_expires_tracked_keys:0
active_defrag_hits:0
active_defrag_misses:0
active_defrag_key_hits:0
active_defrag_key_misses:0

INFO KEYSPACE :

# Keyspace
db1:keys=460000,expires=33771,avg_ttl=9868334

Our redis server is running under Ubuntu 20.04.4 LTS

Thanks.