From: Tom Lane <tgl@sss.pgh.pa.us>
To: Nathan Bossart <nathandbossart@gmail.com>
cc: adam@labkey.com, Bertrand Drouvot <bertranddrouvot.pg@gmail.com>,
        pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #18711: Attempting a connection with a database name longer
 than 63 characters now fails
In-reply-to: <Zz1bvchIEQPT6eTr@nathan>
References: <18711-7503ee3e449d2c47@postgresql.org>
 <3072825.1731866414@sss.pgh.pa.us> <Zzzdc1QLIuFoiTvE@nathan>
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 <3976665.1732057784@sss.pgh.pa.us> <Zz1bvchIEQPT6eTr@nathan>
Comments: In-reply-to Nathan Bossart <nathandbossart@gmail.com>
	message dated "Tue, 19 Nov 2024 21:47:09 -0600"
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Date: Tue, 19 Nov 2024 23:23:13 -0500
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Nathan Bossart <nathandbossart@gmail.com> writes:
> On Tue, Nov 19, 2024 at 06:09:44PM -0500, Tom Lane wrote:
>> Also, we could bypass the multiple lookups unless both the
>> NAMEDATALEN-1'th and NAMEDATALEN-2'th bytes are non-ASCII, which
>> should be rare enough to make it not much of a performance issue.

> I'm admittedly not an expert in the multi-byte code, but since there are
> encodings like LATIN1 that use a byte per character, don't we need to do
> multiple lookups any time the NAMEDATALEN-1'th byte is non-ASCII?

I don't think so, but maybe I'm missing something.  An important
property of backend-legal encodings is that all bytes of a multibyte
character have their high bits set.  Thus if the NAMEDATALEN-2'th
byte does not have that, it is not part of a multibyte character.
That's also the reason we can stop if we reach a high-bit-clear
byte while backing up to earlier bytes.

			regards, tom lane