cache drivers configuration - symfony

Question

I am currently using Symfony with multiple entity managers. I did this accordingly to their example.
Everything works fine in dev and test environment. The connections are established and I can fetch, insert, etc my data as I want to. But then I came accross the problem that I seem to can't establish any connection to my databases in my prod environment: When I try to login it prints some standard error message like "You can not login because of some system problem". So I checked the logs: nothing. Maybe I need to adjust my verbosity level in prod? I couldn't find a way to get some kind of actual error message. Due to this reason I started comparing the configurations for the different environments. And there is a difference for doctrine on those three environments: test and dev don't use any file to overwrite some settings specified in the default doctrine configuration file. Prod does. And because I changed much stuff in my doctrine configuration file it seemed plausible that problem is burried right there. I deleted the additional doctrine configuration file for prod environment and it worked as expected again.
Here is my standard doctrine configuration file (dontrine.yaml):
parameters:
# Adds a fallback DATABASE_URL if the env var is not set.
# This allows you to run cache:warmup even if your
# environment variables are not available yet.
# You should not need to change this value.
env(DATABASE_URL): ''
doctrine:
dbal:
default_connection: admin
connections:
admin:
driver: 'pdo_mysql'
server_version: '5.7'
url: '%env(DB_ADMIN_URL)%'
charset: utf8mb4
default_table_options:
charset: utf8mb4
collate: utf8mb4_unicode_ci
mail:
driver: 'pdo_mysql'
server_version: '5.7'
url: '%env(DB_MAIL_URL)%'
charset: utf8mb4
default_table_options:
charset: utf8mb4
collate: utf8mb4_unicode_ci
host:
driver: 'pdo_mysql'
server_version: '5.7'
url: '%env(DB_HOST_URL)%'
charset: utf8mb4
default_table_options:
charset: utf8mb4
collate: utf8mb4_unicode_ci
orm:
default_entity_manager: admin
auto_generate_proxy_classes: '%kernel.debug%'
entity_managers:
admin:
connection: admin
naming_strategy: doctrine.orm.naming_strategy.underscore
auto_mapping: true
mappings:
Admin:
is_bundle: false
type: annotation
dir: '%kernel.project_dir%/src/Entity/Admin'
prefix: 'App\Entity\Admin'
alias: Admin
mail:
connection: mail
naming_strategy: doctrine.orm.naming_strategy.underscore
mappings:
Mail:
is_bundle: false
type: annotation
dir: '%kernel.project_dir%/src/Entity/Mail'
prefix: 'App\Entity\Mail'
alias: Mail
host:
connection: host
naming_strategy: doctrine.orm.naming_strategy.underscore
mappings:
Host:
is_bundle: false
type: annotation
dir: '%kernel.project_dir%/src/Entity/Host'
prefix: 'App\Entity\Host'
alias: Host
This is my additional doctrine.yaml for prod environment:
doctrine:
orm:
metadata_cache_driver:
type: service
id: doctrine.system_cache_provider
query_cache_driver:
type: service
id: doctrine.system_cache_provider
result_cache_driver:
type: service
id: doctrine.result_cache_provider
services:
doctrine.result_cache_provider:
class: Symfony\Component\Cache\DoctrineProvider
public: false
arguments:
- '#doctrine.result_cache_pool'
doctrine.system_cache_provider:
class: Symfony\Component\Cache\DoctrineProvider
public: false
arguments:
- '#doctrine.system_cache_pool'
framework:
cache:
pools:
doctrine.result_cache_pool:
adapter: cache.app
doctrine.system_cache_pool:
adapter: cache.system
The configuration file for prod environment corresponds to the default one. I tried to add all these additional configurations once per entity manager as I did in the default configuration (for my multiple databases). But I didn't work. I don't actually know what this configuration is responsible for but I guess there is a reason why it has been added to default prod environment. I don't just want to delete it.
My questions are now:
How do I extend the additional configuration properly?
What is the sense in this configuration?