Re: CopyReadLineText optimization

Andrew Dunstan wrote:
> Heikki Linnakangas wrote:
>> Another update attached: It occurred to me that the memchr approach is
>> only safe for server encodings, where the non-first bytes of a
>> multi-byte character always have the hi-bit set.
>>
>
> We currently make the following assumption in the code:
>
>     * These four characters, and the CSV escape and quote characters, are
>     * assumed the same in frontend and backend encodings.
>     *
>
> The four characters are the carriage return, line feed, backslash and dot.
>
> I think the requirement might well actually be somewhat stronger than
> that: i.e. that none of these will appear as a non-first byte in any
> multi-byte client encoding character. If that's right, then we should be
> able to write CopyReadLineText without bothering about multi-byte chars.
> If it's not right then I suspect we have some cases that can fail now
> anyway.

No, we don't require that, and we do handle it correctly. We use
pg_encoding_mblen to determine the length of each character in
CopyReadLineText when the encoding is a client-only encoding, and only
look at the first byte of each character. In CopyReadAttributesText,
where we have a similar loop, we've already transformed the input to
server encoding.

--
   Heikki Linnakangas
   EnterpriseDB   http://www.enterprisedb.com