sql.py: put_table(): Lock the output table in EXCLUSIVE mode before getting its pkey so that an ACCESS SHARE lock is not acquired before EXCLUSIVE (causing a lock upgrade and deadlock). This race condition may not have been previously noticeable because pkey() is cached, so calling it doesn't necessarily execute a query or acquire an ACCESS SHARE lock.
sql.py: put_table(): Lock the output table in EXCLUSIVE mode before getting its pkey so that an ACCESS SHARE lock is not acquired before EXCLUSIVE (causing a lock upgrade and deadlock). This race condition may not have been previously noticeable because pkey() is cached, so calling it doesn't necessarily execute a query or acquire an ACCESS SHARE lock.