Example: I have a database cluster initialized with --locale=ru_RU.UTF-8 (built with NLS). Let's say for some reason, I have client encoding set to LATIN1. All error messages come back like this:
test=> select * from notthere; ERROR: character with byte sequence 0xd0 0x9e in encoding "UTF8" has no equivalent in encoding "LATIN1"
There is no straightforward way for the client to learn that there is a real error message, but it could not be converted.
I think ideally we could make this better in two ways:
1) Send the original error message untranslated. That would require saving the original error message in errmsg(), errdetail(), etc. That would be a lot of work for only the occasional use. But it would also facilitate an occasionally-requested feature of writing untranslated error messages into the server log or the csv log, while sending translated messages to the client (or some variant thereof).
2) Send an indication that there was an encoding problem. Maybe a NOTICE, or an error context? Wiring all this into elog.c looks a bit tricky, however.
We have a similar problem with the server logs. But there there's also an additional problem: if there isn't any character mapping issue we just totally ignore text encoding concerns and log in whatever encoding the client asked the backend to use into the log files. So log files can be a line-by-line mix of UTF-8, ISO-8859-1, and whatever other fun encodings someone asks for. There is *no* way to correctly read such a file since lines don't have any marking as to their encoding and no tools out there support line-by-line differently encoded text files anyway.
I'm not sure how closely it ties in to the issue you mention, but I think it's at least related enough to keep in mind while considering the client_encoding issue.
I suggest (3) "log the message with unmappable characters masked". Though I would definitely like to be able to also send the raw original, along with a field indicating the encoding of the original since it won't be the client_encoding, since we need some way to get to the info.
