PGQ is the queueing solution from Skytools. The Londiste replication solution is a consumer daemon built on PGQ, and the API is accessible for you to create any asynchronous processing facility, based on queuing. Hint: As of 2021 there is a proposal for an additional part of the SQL standard: "SQL/PGQ" (Property Graph Queries) [1]. Don't confuse the information given here with this proposal. What