What:
Use the github.com/jackc/pgx postgresql driver in place of
github.com/lib/pq.
Why:
github.com/lib/pq has some problems with error handling and context
cancellations (i.e. it might even issue queries or DML statements more
than once! see https://github.com/lib/pq/issues/939). The
github.com/jackx/pgx library appears not to have these problems, and
also appears to be better engineered and implemented (in particular, it
doesn't use "exceptions by panic"). It should also give us some
performance improvements in some cases, and even more so if we can use
it directly instead of going through the database/sql layer.
Change-Id: Ia696d220f340a097dee9550a312d37de14ed2044
This system tracks an abstract "api version" from nodes based on
their usage, allowing us to have latching behavior where if a node
ever uses a new api, it can be blocked from using the old api.
This is better than using self-reported semver version information
because the node cannot lie, there's no confusion about what semver
version implies which features, no questions about dev and ci
environments, and no dependencies between reporting the version
and using the new api.
Change-Id: Ifeced5c9ae8e0a16102d79635e176a7d3bdd8ed4
