IPC:MessageQueueInternal
The process is waiting for another process to be attached to a shared message queue.
This wait event typically arises during parallel query execution, logical decoding, or other subsystems that rely on PostgreSQL’s internal message-passing infrastructure.
Context and Meaning
When a query is executed in parallel, the "leader" process and the "worker" processes communicate through shared memory message queues (shm_mq).
For a message queue to function, both the sender and the receiver must "attach" to it. If one process (for example, the leader) has initialized a queue and is waiting for workers to connect and start participating in the communication, it will report the MessageQueueInternal wait event.