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Why are PostgreSQL replication slots are necessary?
A replication slot is a feature in PostgreSQL that ensures that the master server will retain the WAL logs that are needed by the replicas even when they are disconnected from the master. This article will focus on PostgreSQL replication slots. Here is an outline of this blog: What are WAL Files? Why PostgreSQL Replication Slots are Necessary?
How does Wal retention work in PostgreSQL replication?
So while WAL retention is taken care of without manual settings, pg_wal directory space needs to be manually monitored. The changes that take place on the main server via streaming replication are recorded in the WAL segments. These WAL files are sent to the standby server and then replayed.
How to use Barman to backup PostgreSQL server?
When the barman backup command is executed, barman looks for the section [pgdb] in pgdb.conf file. The parameter backup_method defines the type of backup to be taken. In this case backup_method is rsync. Note: For the barman backup command to be successful, password-less ssh authentication must be configured between barman and postgres servers. ? ?
Why is streaming replication introduced in Postgresql 9.0?
In PostgreSQL version 9.0, Streaming Replication was introduced. This feature allowed us to stay more up-to-date when compared to file-based log shipping. Its approach is by transferring WAL records (a WAL file is composed of WAL records) on the fly (merely a record based log shipping), between a master server and one or several standby servers.
How to reduce the risk of failing replication?
If not using replication slots, a common way to reduce the risk of failing replication is to set the wal_keep_segments high enough so that WAL files that might be needed won’t be rotated or recycled. The disadvantage of this approach is that it’s hard to determine what value is best for your setup.
When do you need to re-create replication slots?
Therefore, when failover/switchover is about to happen, you need to re-create the slots you have created. Unused replication slots have to be dropped or deleted.
How to tell if a replication slot is missing?
The function pg_xlog_location_diff give the drift in size : You can use the lag in monitoring tools, as gauge, to monitor your replication. If a standby is missing, you have to check in the log’s standby why. If you use replication slots, you have to check the pg_replication_slots view.
Why does an orphan replication slot cause unbounded disk growth?
An orphan replication slot can cause unbounded disk growth due to piled up WAL files from the master Slave nodes placed under long maintenance (such as days or weeks) and that are tied to a replication slot will have unbounded disk growth due to piled up WAL files from the master