Why so much difference in memory used per process in apache2 between two different systems (Apache Users)

Hi to all,

I already posted this question to stackoverflow.com but no answer after 9 days: https://stackoverflow.com/questions/67439771/why-so-much-difference-in-memory-used-per-process-in-apache2-between-two-differe

I hope the apache gurus in this list can help me :)

I have a pair of Ubuntu dedicated servers...

Server1:
Ubuntu 16.04.7 (64 bits)
16GB RAM
8 Xeon CPU
Apache 2.4.18
MPM mode: prefork

Server2:
Ubuntu server 20.04.2 (64 bits)
32GB RAM
8 Xeon CPU
2.4.41
MPM mode: event

On Server1, each apache2 process uses between 7MB and 18MB of RAM ...

# ps axo 'user rss cmd' | grep apache | grep -v "\(root\|grep\|tomcat\)"
www-data 18232 /usr/sbin/apache2 -k start
www-data 11700 /usr/sbin/apache2 -k start
www-data 11276 /usr/sbin/apache2 -k start
www-data 10792 /usr/sbin/apache2 -k start
www-data 11216 /usr/sbin/apache2 -k start
www-data 11600 /usr/sbin/apache2 -k start
www-data 10336 /usr/sbin/apache2 -k start
www-data 11356 /usr/sbin/apache2 -k start
www-data 11348 /usr/sbin/apache2 -k start
www-data 10980 /usr/sbin/apache2 -k start
www-data 11316 /usr/sbin/apache2 -k start
www-data 6808 /usr/sbin/apache2 -k start

On Server2, each apache2 process uses between 120MB and 130MB of RAM ...

# ps axo 'user rss cmd' | grep apache | grep -v "\(root\|grep\|tomcat\)"
www-data 120436 /usr/sbin/apache2 -k start
www-data 119784 /usr/sbin/apache2 -k start
www-data 128720 /usr/sbin/apache2 -k start
www-data 130208 /usr/sbin/apache2 -k start

Why so much difference in memory used?

After read a few documentation and googleing, I thought about loaded modules, but there are not a lot of difference between each server...

Server1
# apache2 -M
Loaded Modules:
core_module (static)
so_module (static)
watchdog_module (static)
http_module (static)
log_config_module (static)
logio_module (static)
version_module (static)
unixd_module (static)
access_compat_module (shared)
actions_module (shared)
alias_module (shared)
auth_basic_module (shared)
auth_digest_module (shared)
auth_openidc_module (shared)
authn_core_module (shared)
authn_file_module (shared)
authz_core_module (shared)
authz_host_module (shared)
authz_user_module (shared)
autoindex_module (shared)
bw_module (shared)
cgi_module (shared)
dav_module (shared)
dav_fs_module (shared)
dav_lock_module (shared)
deflate_module (shared)
dir_module (shared)
env_module (shared)
expires_module (shared)
fcgid_module (shared)
filter_module (shared)
headers_module (shared)
include_module (shared)
mime_module (shared)
mpm_prefork_module (shared)
negotiation_module (shared)
proxy_module (shared)
proxy_balancer_module (shared)
proxy_fcgi_module (shared)
proxy_http_module (shared)
rewrite_module (shared)
setenvif_module (shared)
slotmem_shm_module (shared)
socache_shmcb_module (shared)
ssl_module (shared)
status_module (shared)
suexec_module (shared)
userdir_module (shared)

Server2
# apache2 -M
Loaded Modules:
core_module (static)
so_module (static)
watchdog_module (static)
http_module (static)
log_config_module (static)
logio_module (static)
version_module (static)
unixd_module (static)
access_compat_module (shared)
aclr_module (shared)
actions_module (shared)
alias_module (shared)
auth_basic_module (shared)
auth_digest_module (shared)
auth_openidc_module (shared)
authn_core_module (shared)
authn_file_module (shared)
authz_core_module (shared)
authz_host_module (shared)
authz_user_module (shared)
autoindex_module (shared)
cgid_module (shared)
dav_module (shared)
dav_fs_module (shared)
dav_lock_module (shared)
deflate_module (shared)
dir_module (shared)
env_module (shared)
fcgid_module (shared)
filter_module (shared)
headers_module (shared)
include_module (shared)
mime_module (shared)
mpm_event_module (shared)
negotiation_module (shared)
proxy_module (shared)
proxy_balancer_module (shared)
proxy_fcgi_module (shared)
proxy_http_module (shared)
remoteip_module (shared)
reqtimeout_module (shared)
rewrite_module (shared)
security2_module (shared)
setenvif_module (shared)
slotmem_shm_module (shared)
socache_shmcb_module (shared)
ssl_module (shared)
status_module (shared)
suexec_module (shared)
unique_id_module (shared)
userdir_module (shared)

I already changed MPM mode from Event to Prefork on Server2, with the same results.

What else can I check to understand this difference?

Thank's!

El contingut d’aquest correu electrònic i els seus annexos és estrictament confidencial. En el cas que no siguis el destinatari i hagis rebut aquest missatge per error, preguem que ho comuniquis al remitent i procedeixis a la seva eliminació, sense difondre, emmagatzemar o copiar el seu contingut. Imprimeix aquest correu només si és necessari.

El contenido de este correo electrónico y sus anexos es estrictamente confidencial. En el caso de que no seas el destinatario y hayas recibido este mensaje por error, rogamos lo comuniques al remitente y procedas a su eliminación, sin difundir, almacenar o copiar su contenido. Imprimir este correo solo si es necesario.

The content of this email and its attachments is strictly confidential. If you are not the recipient and you have received this message by mistake, please notify the sender and proceed to its elimination, without spreading, storing or copying its content. Print this email only if necessary.

Le contenu de cet e-mail et de ses pièces jointes est strictement confidentiel. Dans le cas où vous n'êtes pas le destinataire et avez reçu ce message par erreur, veuillez en informer l'expéditeur et procéder à sa suppression, sans diffuser, stocker ou copier son contenu. Imprimez cet e-mail uniquement si nécessaire.