Hi, I'd like to propose an improvement for pg_recvlogical.
Currently, when pg_recvlogical exits due to SIGINT or SIGTERM, it can terminate after writing decoded output locally but before sending feedback that reflects the latest written position to the server. If pg_recvlogical is restarted after that, the server-side logical replication slot may still remain behind those already-written changes, and the same decoded data can be sent again. Attached patch makes pg_recvlogical send final feedback once more during SIGINT/SIGTERM exit, before sending CopyDone. That gives the server one more chance to advance the slot far enough to avoid resending already-written data after pg_recvlogical is restarted. One note is that this is still only a best-effort improvement. Depending on when SIGINT or SIGTERM arrives, pg_recvlogical may already have written decoded output that the server cannot yet safely treat as confirmed, so duplicate data can still be received after restart. In other words, this patch reduces the likelihood of duplicates, but does not guarantee that they will never happen. I see this as an improvement to pg_recvlogical behavior rather than a bug fix, so I think it should target v20. Regards, -- Fujii Masao
v1-0001-pg_recvlogical-send-final-feedback-on-SIGINT-SIGT.patch
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