During the recent development of parallel operation (parallel create index)[1], a need has been arised for $SUBJECT. The idea is to allow leader backend to rely on number of workers that are successfully started. This API allows leader to wait for all the workers to start or fail even if one of the workers fails to attach. We consider workers started/attached once they are attached to error queue. This will ensure that any error after the workers are attached won't be silently ignored by leader.
I have used wait event as WAIT_EVENT_BGWORKER_STARTUP similar to WaitForReplicationWorkerAttach, but we might want to change it. I have tested this patch by calling this API in nodeGather.c and then introducing failuires at various places: (a) induce fork failure for background workers (force_fork_failure_v1.patch), (b) Exit parallel worker before attaching to the error queue (exit_parallel_worker_before_error_queue_attach_v1.patch) and (c) Exit parallel worker after attaching to the error queue (exit_parallel_worker_after_error_queue_attach_v1.patch). In all above cases, I got the errors as expected. [1] - https://www.postgresql.org/message-id/CAA4eK1KgmdT3ivm1vG%2BrJzKOKeYQU2XLhp6ma5LMHxaG89brsA%40mail.gmail.com -- With Regards, Amit Kapila. EnterpriseDB: http://www.enterprisedb.com
WaitForParallelWorkersToAttach_v1.patch
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modify_gather_to_wait_for_attach_v1.patch
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force_fork_failure_v1.patch
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exit_parallel_worker_before_error_queue_attach_v1.patch
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exit_parallel_worker_after_error_queue_attach_v1.patch
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