Cannot deploy more than 10 units (max_wal_senders limit)

[Zvirovyi]

Same issue in the K8s

Steps to reproduce

1. juju deploy postgresql --channel edge --config profile=testing -n10 and wait them to stabilize
2. juju add-unit postgresql

Expected behavior

Unit is added successfully therefore cluster consists of 11 units.

Actual behavior

New unit stucks in awaiting for member to start.

Versions

Operating system: Ubuntu 24.04.2 LTS

Juju CLI: 3.6.4-genericlinux-amd64

Juju agent: 3.6.4

Charm revision: 576

LXD: 6.3

Log output

2025-03-19T20:30:09Z systemd[1]: snap.charmed-postgresql.patroni.service: Consumed 2.316s CPU time.
2025-03-19T20:30:09Z systemd[1]: Started Service for snap application charmed-postgresql.patroni.
2025-03-19T20:30:13Z charmed-postgresql.patroni[223680]: pg_basebackup: error: connection to server at "10.88.216.188", port 5432 failed: FATAL:  number of requested standby connections exceeds max_wal_senders (currently 10)
2025-03-19T20:30:13Z charmed-postgresql.patroni[223680]: pg_basebackup: removing data directory "/var/snap/charmed-postgresql/common/var/lib/postgresql"
2025-03-19T20:30:20Z charmed-postgresql.patroni[223681]: pg_basebackup: error: connection to server at "10.88.216.188", port 5432 failed: FATAL:  number of requested standby connections exceeds max_wal_senders (currently 10)
2025-03-19T20:30:20Z charmed-postgresql.patroni[223681]: pg_basebackup: removing data directory "/var/snap/charmed-postgresql/common/var/lib/postgresql"
2025-03-19T20:30:23Z charmed-postgresql.patroni[223683]: pg_basebackup: error: connection to server at "10.88.216.188", port 5432 failed: FATAL:  number of requested standby connections exceeds max_wal_senders (currently 10)
2025-03-19T20:30:23Z charmed-postgresql.patroni[223683]: pg_basebackup: removing data directory "/var/snap/charmed-postgresql/common/var/lib/postgresql"
2025-03-19T20:30:31Z charmed-postgresql.patroni[223778]: pg_basebackup: error: connection to server at "10.88.216.188", port 5432 failed: FATAL:  number of requested standby connections exceeds max_wal_senders (currently 10)
2025-03-19T20:30:31Z charmed-postgresql.patroni[223778]: pg_basebackup: removing data directory "/var/snap/charmed-postgresql/common/var/lib/postgresql"

Additional context

I think including max_wal_senders and max_replication_slots config options will resolve this issue and add an abiltiy to include charm checks based on that value.

[syncronize-issues-to-jira]

Thank you for reporting your feedback to us!

The internal ticket has been created: https://warthogs.atlassian.net/browse/DPE-6852.

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