Por que o Memcached está vazio

Adicionei o memcached à pilha LAMP e ao Wordpress e tudo parece bem, exceto que a memória do memcached está vazia. Quando verifico com memcdump --servers=127.0.0.1 ele não retorna nada. Além disso, quando me conecto via telnet 127.0.0.1 11211 , parece estar em execução, mas vazio - os itens de estatísticas não retornam nada e

placas de estatísticas

STAT active_slabs 0
STAT total_malloced 0

O que estou perdendo aqui?

Abaixo estão todas as verificações que fiz

saída completa de estatísticas do memcached

stats
STAT pid 37127
STAT uptime 12198
STAT time 1706711922
STAT version 1.5.22
STAT libevent 2.1.11-stable
STAT pointer_size 64
STAT rusage_user 1.447142
STAT rusage_system 0.916591
STAT max_connections 1024
STAT curr_connections 1
STAT total_connections 14
STAT rejected_connections 13
STAT connection_structures 2
STAT reserved_fds 20
STAT cmd_get 1
STAT cmd_set 0
STAT cmd_flush 0
STAT cmd_touch 0
STAT cmd_meta 0
STAT get_hits 0
STAT get_misses 1
STAT get_expired 0
STAT get_flushed 0
STAT delete_misses 0
STAT delete_hits 0
STAT incr_misses 0
STAT incr_hits 0
STAT decr_misses 0
STAT decr_hits 0
STAT cas_misses 0
STAT cas_hits 0
STAT cas_badval 0
STAT touch_hits 0
STAT touch_misses 0
STAT auth_cmds 0
STAT auth_errors 0
STAT bytes_read 11417
STAT bytes_written 6580
STAT limit_maxbytes 67108864
STAT accepting_conns 1
STAT listen_disabled_num 0
STAT time_in_listen_disabled_us 0
STAT threads 4
STAT conn_yields 0
STAT hash_power_level 16
STAT hash_bytes 524288
STAT hash_is_expanding 0
STAT slab_reassign_rescues 0
STAT slab_reassign_chunk_rescues 0
STAT slab_reassign_evictions_nomem 0
STAT slab_reassign_inline_reclaim 0
STAT slab_reassign_busy_items 0
STAT slab_reassign_busy_deletes 0
STAT slab_reassign_running 0
STAT slabs_moved 0
STAT lru_crawler_running 0
STAT lru_crawler_starts 5100
STAT lru_maintainer_juggles 12246
STAT malloc_fails 0
STAT log_worker_dropped 0
STAT log_worker_written 0
STAT log_watcher_skipped 0
STAT log_watcher_sent 0
STAT bytes 0
STAT curr_items 0
STAT total_items 0
STAT slab_global_page_pool 0
STAT expired_unfetched 0
STAT evicted_unfetched 0
STAT evicted_active 0
STAT evictions 0
STAT reclaimed 0
STAT crawler_reclaimed 0
STAT crawler_items_checked 0
STAT lrutail_reflocked 0
STAT moves_to_cold 0
STAT moves_to_warm 0
STAT moves_within_lru 0
STAT direct_reclaims 0
STAT lru_bumps_dropped 0
END

Estou executando PHP em php-fpm (v7.4) no Ubuntu 20.04 e Apache 2.4. Instalei o memcached (v1.5.22) via apt junto com o pacote php7.4-memcached e libmemcached-tools

netstat mostra que está escutando na porta 11211

tcp    0    0 127.0.0.1:11211  0.0.0.0:*  LISTEN 37127/memcached 

tudo roda em localhost, então mantive o padrão /etc/memcached.conf

# run as a daemon
-d 
# memory
-m 64
# connection port
-p 11211
# user
-u memcache
# listen
-l 127.0.0.1
# pidfile
-P /var/run/memcached/memcached.pid

o arquivo do processo existe

-rw-r--r-- 1 memcache memcache 6 Jan 31 12:15 /var/run/memcached/memcached.pid

e o processo é executado

ps -eaf | grep memcached
memcache   37127       1  0 12:15 ?        00:00:02 /usr/bin/memcached -m 64 -p 11211 -u memcache -l 127.0.0.1 -P /var/run/memcached/memcached.pid

o serviço está em execução (status do serviço memcached)

Loaded: loaded (/lib/systemd/system/memcached.service; enabled; vendor preset: enabled)
     Active: active (running) since Wed 2024-01-31 12:15:26 CET; 3h 19min ago
       Docs: man:memcached(1)
   Main PID: 37127 (memcached)
      Tasks: 10 (limit: 5846)
     Memory: 2.1M
     CGroup: /system.slice/memcached.service
             └─37127 /usr/bin/memcached -m 64 -p 11211 -u memcache -l 127.0.0.1 -P /var/run/memcached/memcached.pid

Jan 31 12:15:26 www systemd[1]: Started memcached daemon.

A configuração do módulo php (/etc/php/7.4/mods-available/memcached.ini) não tem muito

memcached.ini
; priority=25
extension=memcached.so
; You need to install php-igbinary package to use igbinary serializer
; and php-msgpack to use msgpack serializer
memcached.serializer=php