Re: More efficient truncation of pg_stat_activity query strings

> Check the information the pg_*_mblen use / how the relevant encodings
> work. Will be something like
> int
> pg_utf_mblen(const unsigned char *s)
> {
> int len;
>
> if ((*s & 0x80) == 0)
> len = 1;
> else if ((*s & 0xe0) == 0xc0)
> len = 2;
> else if ((*s & 0xf0) == 0xe0)
> len = 3;
> else if ((*s & 0xf8) == 0xf0)
> len = 4;
> #ifdef NOT_USED
> else if ((*s & 0xfc) == 0xf8)
> len = 5;
> else if ((*s & 0xfe) == 0xfc)
> len = 6;
> #endif
> else
> len = 1;
> return len;
> }
>
> As you can see, only the first character (*s) is accessed to determine
> the length/width of the multibyte-character. That's afaict the case for
> all server-side encodings.

So your idea is just storing cmd_str into st_activity, which might be
clipped in the middle of multibyte character. And the reader of the
string will call pg_mbclipen() when it needs to read the string. Yes,
I think it works except for gb18030 by the reason you said.

However, if we could have variants of mblen functions with additional
parameter: input string length, then we could remove this inconstancy.
I don't know if this is overkill or not, though.

Best regards,
--
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
Japanese:http://www.sraoss.co.jp