It's possible I'm misreading this, but I'm thinking that commits
cc5f8136 and ab9e0e71 added a few tranches which we need to add to the docs.
session_dsa, session_record_table, session_typmod_table, and
shared_tuplestore
https://www.postgresql.org/docs/current/monitoring-stats.html#WAIT-EVENT-TABLE
-Jeremy
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Jeremy Schneider
Database Engineer
Amazon Web Services