Re: Understanding DateStyle guc in startup packet

Long story short: it might be nice to decouple pgjdbc from requiring
DateStyle=ISO, however, it does not look like a walk in the park to me.

I guess here's the line that configures DateStyle ISO:
https://github.com/pgjdbc/pgjdbc/blob/d9e20874590f59543c39a99b824e09344f00a813/pgjdbc/src/main/java/org/postgresql/core/v3/ConnectionFactoryImpl.java#L409

It looks like options come after DateStyle.

At the same time, for some reason related to COPY processing, the driver
asserts DateStyle must start with ISO:
https://github.com/pgjdbc/pgjdbc/issues/131

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For historical reasons, pgjdbc often sends timestamps and dates as
text-encoded literals, so it needs the backend to recognize the value
properly.
The reason is that Java's `setTimestamp()` does not distinguish between
timestamp and timestamptz, so the driver can't use Oid for
timestamp/timestamptz,
so it falls back to text encoding with Oid "unknown".

I have not explored if the server would parse the timestamps appropriately.

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At the same time, DateStyle might affect text representation of the
timestamps, and the driver is not prepared to parse various flavours of
timestamp representation.
A way out might be to make sure pgjdbc always requires binary encoding when
receiving timestamp/timestamptz/date.
However, it might be trickier when processing arrays or structs as
requiring all the arrays and structs to be in binary would take a bit of
time as well.

Vladimir