Request for Guidance on Recommended ulimit/Open File Settings for PostgreSQL 17 Multi-Cluster Environment

Hi Team,

We are currently migrating our database environments from IBM Db2 to
PostgreSQL 17.6 on AlmaLinux and would like some guidance/best practices
around recommended ulimit (open file descriptor) settings for PostgreSQL.

Environment details:

- OS: AlmaLinux
- PostgreSQL Version: 17.6
- Deployment Model: Multiple PostgreSQL clusters (~10 clusters) running
on the same server
- All PostgreSQL instances are managed through systemd services using a
template service (postgresql(at)(dot)service)
- Workload includes ETL, PgBouncer

Current DB2 Setting:

Max open files = 65535

We would like clarification on:

1. Is increasing the open file limit (ulimit -n) recommended/required
for PostgreSQL in such multi-cluster production environments?
2. What would be the recommended LimitNOFILE value for PostgreSQL
considering:
- multiple clusters on same host
- production workloads
- PgBouncer usage
- ETL-heavy processing

Current PostgreSQL service template:

[Unit]
Description=PostgreSQL 17 database server instance %i
After=network.target
[Service]
Type=forking
User=postgres
Group=postgres

EnvironmentFile=/etc/postgresql/%i.env

ExecStart=/volumes/pg/pgsql-17/bin/pg_ctl start -D ${PGDATA} -o "-p
${PGPORT}" -l ${PGLOG}/postgresql.log -s -w -t 300
ExecStop=/volumes/pg/pgsql-17/bin/pg_ctl stop -D ${PGDATA} -s -m fast
ExecReload=/volumes/pg/pgsql-17/bin/pg_ctl reload -D ${PGDATA} -s
[Install]
WantedBy=multi-user.target

Reg,
Hussain