whether I can add a new encoding?

The pg_wchar.h file comments "We must avoid renumbering any backend encoding until libpq's major version number is increased beyond 5", Can I add a new server-side encoding, GBK18030, and place it after PG_KOI8U in PG10.6? 

What's GBK18030? Can you please give a pointer to a specification of
GBK18030?

Best reagards,
--
Tatsuo Ishii
SRA OSS LLC
English: http://www.sraoss.co.jp/index_en/
Japanese:http://www.sraoss.co.jp

"=?ISO-8859-1?B?UGFuZG9yYQ==?=" <yeyukui@qq.com> writes:

The pg_wchar.h file comments "We must avoid renumbering any backend encoding until libpq's major version number is increased beyond 5", Can I add a new server-side encoding, GBK18030, and place it after PG_KOI8U in PG10.6?

What is GBK18030? If it's related to either GBK or GB18030,
then it'd be unsafe to use as a server encoding because it's not a
strict ASCII superset (that is, it has multibyte characters in
which not all bytes have the high bit set). The lack of room for
a new server encoding in the pg_enc enum has seemed like a mostly
hypothetical problem because of that restriction.

regards, tom lane