Frequent Out of Memory for service(config)

[Root Kev]

Hello Group,

We have dovecot deployed as solely a Pop3 service that is used by our
applications to pass mail from one application to another internally.  We
have roughly 4 applications that connect to the Pop3 service every 2
seconds, to check for new messages and pop them for processing if they are
present.  Depending on the site, we have between 1024-2048MB of memory set
for default_vsz_limit.  In all systems we see the Out of memory alert
several times a day. We previously did not see this at all when running on
CentOS6, with less memory.

We have tried increasing the memory to the vsz_limit up to 2gb without
success.

We are running on CentOS 7 servers, running dovecot 2.3.6 (7eab80676) (from
the dovecot repo).

Can anyone advise any other settings that could be modified in order to
correct these out of memory issues?

# dovecot -n
# 2.3.6 (7eab80676): /etc/dovecot/dovecot.conf
# OS: Linux 3.10.0-957.5.1.el7.x86_64 x86_64 CentOS Linux release 7.6.1810
(Core)
# Hostname: ****** #<modified for security>
auth_cache_size = 10 M
auth_verbose = yes
default_vsz_limit = 1 G
instance_name = Pop3 Mail Service
listen = 10.*.*.* #<modified for security>
log_path = /var/log/dovecot.log
login_greeting = Pop3 Mail Service
login_trusted_networks = 10.*.*.* 10.*.*.* 10.*.*.* 10.*.*.* 10.*.*.*
#<modified for security>
mail_location = maildir:~/Maildir
namespace inbox {
  inbox = yes
  location =
  mailbox Drafts {
    special_use = \Drafts
  }
  mailbox Junk {
    special_use = \Junk
  }
  mailbox Sent {
    special_use = \Sent
  }
  mailbox "Sent Messages" {
    special_use = \Sent
  }
  mailbox Trash {
    special_use = \Trash
  }
  prefix =
}
passdb {
  args = cache_key=#hidden_use-P_to_show#
  driver = pam
}
protocols = pop3
ssl_cert = </etc/pki/dovecot/certs/dovecot.pem
ssl_key = # hidden, use -P to show it
userdb {
  driver = passwd
}
verbose_ssl = yes

May 10 06:44:05 config: Fatal: pool_system_malloc(8192): Out of memory
May 10 06:44:05 config: Fatal: master: service(config): child 27887
returned error 83 (Out of memory (service config { vsz_limit=1024 MB }, you
may need to increase it) - set CORE_OUTOFMEM=1 environment to get core dump)
May 10 14:56:31 config: Fatal: pool_system_malloc(8192): Out of memory
May 10 14:56:31 config: Fatal: master: service(config): child 2495 returned
error 83 (Out of memory (service config { vsz_limit=1024 MB }, you may need
to increase it) - set CORE_OUTOFMEM=1 environment to get core dump)
May 10 23:09:02 config: Fatal: pool_system_malloc(8192): Out of memory
May 10 23:09:02 config: Fatal: master: service(config): child 10581
returned error 83 (Out of memory (service config { vsz_limit=1024 MB }, you
may need to increase it) - set CORE_OUTOFMEM=1 environment to get core dump)
May 11 10:18:43 config: Fatal: pool_system_malloc(8192): Out of memory
May 11 10:18:43 config: Fatal: master: service(config): child 30511
returned error 83 (Out of memory (service config { vsz_limit=1024 MB }, you
may need to increase it) - set CORE_OUTOFMEM=1 environment to get core dump)
May 11 18:30:59 config: Fatal: pool_system_malloc(1608): Out of memory
May 11 18:30:59 config: Fatal: master: service(config): child 12134
returned error 83 (Out of memory (service config { vsz_limit=1024 MB }, you
may need to increase it) - set CORE_OUTOFMEM=1 environment to get core dump)
May 12 02:57:28 config: Fatal: pool_system_malloc(8192): Out of memory
May 12 02:57:28 config: Fatal: master: service(config): child 24940
returned error 83 (Out of memory (service config { vsz_limit=1024 MB }, you
may need to increase it) - set CORE_OUTOFMEM=1 environment to get core dump)
May 12 11:07:34 config: Fatal: pool_system_malloc(8192): Out of memory
May 12 11:07:35 config: Fatal: master: service(config): child 8203 returned
error 83 (Out of memory (service config { vsz_limit=1024 MB }, you may need
to increase it) - set CORE_OUTOFMEM=1 environment to get core dump)
May 12 19:17:52 config: Fatal: pool_system_malloc(8192): Out of memory
May 12 19:17:52 config: Fatal: master: service(config): child 14623
returned error 83 (Out of memory (service config { vsz_limit=1024 MB }, you
may need to increase it) - set CORE_OUTOFMEM=1 environment to get core dump)
May 13 03:26:34 config: Fatal: pool_system_malloc(8192): Out of memory
May 13 03:26:35 config: Fatal: master: service(config): child 21479
returned error 83 (Out of memory (service config { vsz_limit=1024 MB }, you
may need to increase it) - set CORE_OUTOFMEM=1 environment to get core dump)
May 13 11:35:42 config: Fatal: pool_system_malloc(8192): Out of memory
May 13 11:35:43 config: Fatal: master: service(config): child 26900
returned error 83 (Out of memory (service config { vsz_limit=1024 MB }, you
may need to increase it) - set CORE_OUTOFMEM=1 environment to get core dump)
May 13 19:34:26 config: Fatal: pool_system_malloc(8192): Out of memory
May 13 19:34:26 config: Fatal: master: service(config): child 32187
returned error 83 (Out of memory (service config { vsz_limit=1024 MB }, you
may need to increase it) - set CORE_OUTOFMEM=1 environment to get core
dump).

Thanks,

Kevin
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