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Improve make_greater_string() with encoding-specific incrementers.

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This infrastructure doesn't in any way guarantee that the character
we produce will sort before the one we incremented; but it does at least
make it much more likely that we'll end up with something that is a valid
character, which improves our chances.

Kyotaro Horiguchi, with various adjustments by me.
This commit is contained in:
Robert Haas
2011-10-29 14:22:20 -04:00
parent 51eba98cf4
commit 78d523b633
3 changed files with 297 additions and 28 deletions
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65
src/backend/utils/adt/selfuncs.c
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@ -5665,6 +5665,19 @@ pattern_selectivity(Const *patt, Pattern_Type ptype)
}
/*
* For bytea, the increment function need only increment the current byte
* (there are no multibyte characters to worry about).
*/
static bool
byte_increment(unsigned char *ptr, int len)
{
if (*ptr >= 255)
return false;
(*ptr)++;
return true;
}
/*
* Try to generate a string greater than the given string or any
* string it is a prefix of. If successful, return a palloc'd string
@ -5704,6 +5717,7 @@ make_greater_string(const Const *str_const, FmgrInfo *ltproc, Oid collation)
int len;
Datum cmpstr;
text *cmptxt = NULL;
mbcharacter_incrementer charinc;
/*
* Get a modifiable copy of the prefix string in C-string format, and set
@ -5765,29 +5779,33 @@ make_greater_string(const Const *str_const, FmgrInfo *ltproc, Oid collation)
}
}
if (datatype == BYTEAOID)
charinc = &byte_increment;
else
charinc = pg_database_encoding_character_incrementer();
while (len > 0)
{
unsigned char *lastchar = (unsigned char *) (workstr + len - 1);
unsigned char savelastchar = *lastchar;
int charlen;
unsigned char *lastchar;
Const *workstr_const;
if (datatype == BYTEAOID)
charlen = 1;
else
charlen = len - pg_mbcliplen(workstr, len, len - 1);
lastchar = (unsigned char *) (workstr + len - charlen);
/*
* Try to generate a larger string by incrementing the last byte.
* Try to generate a larger string by incrementing the last character
* (for BYTEA, we treat each byte as a character).
*/
while (*lastchar < (unsigned char) 255)
if (charinc(lastchar, charlen))
{
Const *workstr_const;
(*lastchar)++;
if (datatype != BYTEAOID)
{
/* do not generate invalid encoding sequences */
if (!pg_verifymbstr(workstr, len, true))
continue;
workstr_const = string_to_const(workstr, datatype);
}
else
if (datatype == BYTEAOID)
workstr_const = string_to_bytea_const(workstr, len);
else
workstr_const = string_to_const(workstr, datatype);
if (DatumGetBool(FunctionCall2Coll(ltproc,
collation,
@ -5806,20 +5824,11 @@ make_greater_string(const Const *str_const, FmgrInfo *ltproc, Oid collation)
pfree(workstr_const);
}
/* restore last byte so we don't confuse pg_mbcliplen */
*lastchar = savelastchar;
/*
* Truncate off the last character, which might be more than 1 byte,
* depending on the character encoding.
* Truncate off the last character or byte.
*/
if (datatype != BYTEAOID && pg_database_encoding_max_length() > 1)
len = pg_mbcliplen(workstr, len, len - 1);
else
len -= 1;
if (datatype != BYTEAOID)
workstr[len] = '\0';
len -= charlen;
workstr[len] = '\0';
}
/* Failed... */