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From: mahamood hussain <[email protected]>
To: Pgsql-admin <[email protected]>
Subject: Request for Guidance on Recommended ulimit/Open File Settings for PostgreSQL 17 Multi-Cluster Environment
Date: Mon, 25 May 2026 22:46:33 +0530
Message-ID: <CAGc_7H=OAK6sf0EEMv-_9fcAM76UFT=BzzfWs-sTSjsFj43vEA@mail.gmail.com> (raw)

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 ([email protected])
   - 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

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