hello - first a thank-you to this list for all previous questions answered here!
In our cluster, we're using read-only replicas for answering postgis geo queries. Often, i see multiple queries coming in concurrently & regularly taking 2-10 seconds. When looking closer at these queries, i see they all use an ExclusiveLock.
And when this is the query traffic, there can be increasing replication lag.
But also - there can be waves of tx cancellation due to conflicts, ie. replication.
note that in this setup, pg_vacuum_defer_cleanup_age = 0 so the cancels make sense to me.
So the simple question: do ExclusiveLock compete or block application of wal logs on read replicas?