CREATE statement creates a row in a catalog during a subtransaction, but
that subtransaction gets rolled back to the savepoint, and other things
happen which trigger page pruning on the catalog page, and the original
transaction (perhaps in a new subtransaction) then does another CREATE
operation, a new row can get inserted into the same catalog at the same
TID.  During logical decoding, this can trigger an Assertion, and in
non-assert builds, could silently corrupt the decoder's catalog visibility,
which could cause it to produce incorrect output (wrong column mappings,
etc.)