The queryId depends on oids, so it is not stable enough for some purposes.
For example, to create a SQL identifier that survives across a server
upgrade, or that can be shipped to another database, the queryId isn't
usable.
The apg_plan_mgmt extensions keeps both its own stable SQL identifier as
well as the queryId, so it can be used to join to pg_stat_statements if
desired. If we were to standardize on one SQL identifier, it should be
stable enough to survive a major version upgrade or to be the same in
different databases.
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Jim Finnerty, AWS, Amazon Aurora PostgreSQL
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