Because logical replication is based on a similar architecture as physical streaming replication, the monitoring on a publication node is similar to monitoring of a physical replication master (see Section 18.104.22.168).
The monitoring information about subscription is visible in
pg_stat_subscription. This view contains one
row for every subscription worker. A subscription can have zero
or more active subscription workers depending on its state.
Normally, there is a single apply process running for an enabled subscription. A disabled subscription or a crashed subscription will have zero rows in this view. If the initial data synchronization of any table is in progress, there will be additional workers for the tables being synchronized.
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