> What I would want to investigate after seeing such a signal is not > necessarily what happened to be blocking that particular VACUUM > operation at some earlier point, but what is holding the xid horizon > back now. For that purpose, a view exposing the current xid/xmin > holders seems more useful and less misleading than adding a > best-effort blocker guess to the VACUUM log.
I've been working on a view like this. It shows the horizon contribution for each backend, prepared xact, replication slot, and HSF walsender, broken down by class. It also shows - for each contributor - how the horizon would shift if that holder were removed. Shinya said [1] that we could have a view in the future. We could have both the logging and the view call a single function that reads the procArray and other sources to gather the horizon information. I think the logging and the view would complement each other. Should I start another thread? [1] https://www.postgresql.org/message-id/caozeurtnvkvvsckeeoy0wwfzyqo+j_myxwkjrtej_zyydte...@mail.gmail.com -- Scott Ray
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