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How to Fix PostgreSQL Replication Slot Creation Errors ​

May 2026

If PostgreSQL cannot create the replication slot, the source is not ready for logical replication yet.

Short Answer ​

PostgreSQL replication slot creation failed usually means the database is not ready for logical replication. In Skippr, Postgres CDC uses WAL logical replication with the pgoutput plugin, creates a replication slot and publication, and then streams row-level changes. If the slot cannot be created, the failure is usually in those source prerequisites, not in the destination.

The docs give three checks that matter first: wal_level = logical, a user with the REPLICATION attribute or superuser access, and max_replication_slots set high enough to allow at least one slot. If any of those are missing, CDC never reaches the point where it can start streaming changes.

It also helps to confirm which slot name Skippr is trying to use. With CDC enabled, the default is skippr_slot, but a custom replication_slot_name changes the troubleshooting target.

Why This Error Happens ​

A replication slot is not just another object to create. It is part of the durability contract for CDC. Skippr stores the committed LSN after each committed batch and reuses the same slot on restart so PostgreSQL can retain WAL until those changes are confirmed.

That is why slot-creation failures are worth fixing at the source boundary. If the slot never exists, there is no reliable resume point, and the rest of the CDC path never gets a stable foundation.

  • The Postgres server is not running with wal_level = logical, or that change was made in config but not applied with a restart.
  • The replication user can connect to the database but does not have the REPLICATION attribute and is not a superuser.
  • The server does not have replication-slot capacity available because max_replication_slots is too low for the environment.

How to Fix It with Skippr ​

Start with the live Postgres settings, not with what the team thinks is in postgresql.conf. Logical replication problems often come from configuration drift between a parameter file, a managed-database setting, and the values the running server is actually using.

Once the three prerequisites are correct, retry the same CDC configuration instead of changing downstream tables or destinations. This is a source-side setup problem, and it usually becomes boring again as soon as PostgreSQL is truly ready for logical replication.

  • Confirm the source config has cdc_enabled: true and note the replication_slot_name and publication_name in use.
  • Verify the running server is using wal_level = logical and apply a restart if the platform requires one.
  • Ensure the Postgres user used for CDC has the REPLICATION attribute or superuser access.
  • Check that max_replication_slots allows at least one usable slot for this source.
  • Reconnect the Postgres source and retry the CDC run so Skippr can create the slot and publication cleanly.

When Skippr Is the Better Path ​

This kind of issue is easier in Skippr because the CDC prerequisites are explicit. You can isolate the slot, publication, and user requirements directly instead of guessing which hidden replication worker failed.

Once Postgres CDC is healthy, the same project can continue into supported final-state destinations without inventing a new handoff between source setup and warehouse behavior.