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From: mahamood hussain <hussain.ieg@gmail.com>
Date: Mon, 25 May 2026 22:46:33 +0530
Message-ID: 
 <CAGc_7H=OAK6sf0EEMv-_9fcAM76UFT=BzzfWs-sTSjsFj43vEA@mail.gmail.com>
Subject: Request for Guidance on Recommended ulimit/Open File Settings for
 PostgreSQL 17 Multi-Cluster Environment
To: Pgsql-admin <pgsql-admin@lists.postgresql.org>
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 <https://www.postgresql.org/message-id/CAGc_7H%3DOAK6sf0EEMv-_9fcAM76UFT%3DBzzfWs-sTSjsFj43vEA%40mail.gmail.com>
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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@.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

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<div dir=3D"ltr"><p class=3D"gmail-isSelectedEnd">Hi Team,</p><p class=3D"g=
mail-isSelectedEnd">We are currently migrating our database environments fr=
om IBM Db2 to PostgreSQL 17.6 on AlmaLinux and would like some guidance/bes=
t practices around recommended <code dir=3D"ltr">ulimit</code> (open file d=
escriptor) settings for PostgreSQL.</p><p class=3D"gmail-isSelectedEnd">Env=
ironment details:</p><ul><li>OS: AlmaLinux</li><li>PostgreSQL Version: 17.6=
</li><li>Deployment Model: Multiple PostgreSQL clusters (~10 clusters) runn=
ing on the same server</li><li>All PostgreSQL instances are managed through=
 <code dir=3D"ltr">systemd</code> services using a template service (<code =
dir=3D"ltr">postgresql@.service</code>)</li><li>Workload includes ETL, PgBo=
uncer</li></ul><p class=3D"gmail-isSelectedEnd">Current DB2 Setting:</p><pr=
e dir=3D"ltr"><code dir=3D"ltr">Max open files =3D 65535</code></pre><p cla=
ss=3D"gmail-isSelectedEnd">We would like clarification on:</p><ol start=3D"=
1"><li>Is increasing the open file limit (<code dir=3D"ltr">ulimit -n</code=
>) recommended/required for PostgreSQL in such multi-cluster production env=
ironments?</li><li>What would be the recommended <code dir=3D"ltr">LimitNOF=
ILE</code> value for PostgreSQL considering:<ul><li>multiple clusters on sa=
me host</li><li>production workloads</li><li>PgBouncer usage</li><li>ETL-he=
avy processing</li></ul></li></ol><p class=3D"gmail-isSelectedEnd">Current =
PostgreSQL service template:</p><pre dir=3D"ltr"><code dir=3D"ltr"><span cl=
ass=3D"gmail-text-token-text-primary gmail-cursor-text gmail-rounded-sm">[U=
nit]</span>
Description=3DPostgreSQL 17 database server instance %i
After=3Dnetwork.target

<span class=3D"gmail-text-token-text-primary gmail-cursor-text gmail-rounde=
d-sm">[Service]</span>
Type=3Dforking
User=3Dpostgres
Group=3Dpostgres

EnvironmentFile=3D/etc/postgresql/%i.env

ExecStart=3D/volumes/pg/pgsql-17/bin/pg_ctl start -D ${PGDATA} -o &quot;-p =
${PGPORT}&quot; -l ${PGLOG}/postgresql.log -s -w -t 300
ExecStop=3D/volumes/pg/pgsql-17/bin/pg_ctl stop -D ${PGDATA} -s -m fast
ExecReload=3D/volumes/pg/pgsql-17/bin/pg_ctl reload -D ${PGDATA} -s

<span class=3D"gmail-text-token-text-primary gmail-cursor-text gmail-rounde=
d-sm">[Install]</span>
WantedBy=3Dmulti-user.target<br><br>Reg,<br>Hussain</code></pre></div>

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