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.