Thinking further about the use of emergency mode, we have this: "If for some reason autovacuum fails to clear old XIDs from a table, the system will begin to emit warning messages like this when the database's oldest XIDs reach forty million transactions from the wraparound point:
WARNING: database "mydb" must be vacuumed within 39985967 transactions HINT: To avoid a database shutdown, execute a database-wide VACUUM in that database. " It seems people tend not to see these warnings if they didn't already have some kind of monitoring which would prevent them from getting here in the first place. But if they do, the hint should mention the emergency option here, too. This puts Justin's idea upthread in a new light -- if the admin does notice this warning, then emergency mode should indeed vacuum the oldest tables first, since autovacuum is not (yet) smart enough to do that. I'll pursue that as a follow-up. -- John Naylor EDB: http://www.enterprisedb.com
