pg_async.rs

Asynchronous, HA (master-master) PostgreSQL driver on top of libpq.

Vision

• Designed to work with a master-master replicated database, such as BDR (but standalone databases are supported too).
• Uses libpq, leveraging it's asynchronous support.
• Maintains an asynchronous connection to every node of the replicated cluster.
• Pings the nodes (with SELECT 1) to see who's closer/faster.
• Every operation is a separate transaction.
• If a node fails, the operation is transparently retried on another node.
• Operations are exposed as futures.
• futures are backed by a thread or two and can be used without a tokio reactor (because KISS).
• Fast mode: send the operation to every node and return the first answer.
• Pin mode: send the operation to one of the nodes only (useful to avoid some of the master-master conflicts).
• There is a JSON helper converting table rows to serde_json objects.
• If the operation wasn't pipelined already, dropping a Future allows the driver to cancel it.
• Database-level timeouts can be used to terminate slow operations early.

Notes

The combination of libpq and OpenSSL doesn't work very well during PostgreSQL server restarts. I've seen libpq SEGV-crash reliably when the OpenSSL layer is enabled. For the driver to properly work around PostgreSQL server unavailability and restarts I recommend adding the "sslmode=disable" disabler to the connection strings.