Postgres Show Replication Slots: Step-by-Step Guide

Learn to postgres show replication slots effectively. Replication slots ensure data consistency in PostgreSQL setups, preventing WAL loss during outages. Vital for high-availability clusters.

This guide covers querying, managing, and troubleshooting slots from version 9.4 to 17. Use SQL commands and pgAdmin for monitoring.

Querying Replication Slots

Start with basic SELECT to list all slots.

  • 1. Connect to PostgreSQL: psql -U postgres
  • 2. Run: SELECT * FROM pg_replication_slots;
  • 3. Review slot_name, plugin, slot_type, active.

Interpreting Slot Details

Key columns: wal_status, safe_wal_size indicate health.

  • 1. Check restart_lsn for lag.
  • 2. Note database and xmin for logical slots.
  • 3. Monitor confirmed_flush for physical.

Creating New Replication Slots

Set up slots for streaming replication.

  • 1. SELECT pg_create_physical_replication_slot('slotname');
  • 2. For logical: pg_create_logical_replication_slot('slotname', 'pgoutput');
  • 3. Verify with show command.

Dropping Unused Slots

Free resources by removing inactive slots.

  • 1. Ensure no subscriber uses it.
  • 2. SELECT pg_drop_replication_slot('slotname');
  • 3. Confirm deletion.

Troubleshooting Common Issues

Handle slot bloat and WAL accumulation.

  • 1. Check for inactive subscribers.
  • 2. Advance slot: pg_replication_slot_advance()
  • 3. Vacuum WAL if needed.

Monitoring with Extensions

Use pg_stat_replication for advanced insights.

  • 1. Install pgBadger or check_postgres.pl.
  • 2. Set up alerts for slot lag.
  • 3. Integrate with Prometheus.

Frequently Asked Questions

What is pg_replication_slots?

A system view showing all replication slots, their status, and WAL positions in PostgreSQL.

How to show only active slots?

SELECT * FROM pg_replication_slots WHERE active = true;

What if a slot is inactive?

Drop it if unused to prevent WAL bloat: SELECT pg_drop_replication_slot('slotname');

Difference between physical and logical slots?

Physical for exact binary copies; logical for filtered, decoded changes.

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