sync after unroll

[tpolecat]

Per the doc:

At completion of each series of extended-query messages, the frontend should issue a Sync message. This parameterless message causes the backend to close the current transaction if it's not inside a BEGIN/COMMIT transaction block ("close" meaning to commit if no error, or roll back if error). Then a ReadyForQuery response is issued.

Not doing this can lead to weird behavior if you try to do things on the session after executing a portal (async notifications are stopped, for example).