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Fix regex_fixed_prefix() to cope reasonably well with regex patterns of the

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form '^(foo)$'.  Before, these could never be optimized into indexscans.
The recent changes to make psql and pg_dump generate such patterns (for \d
commands and -t and related switches, respectively) therefore represented
a big performance hit for people with large pg_class catalogs, as seen in
recent gripe from Erik Jones.  While at it, be more paranoid about
case-sensitivity checking in multibyte encodings, and fix some other
corner cases in which a regex might be interpreted too liberally.
This commit is contained in:
Tom Lane
2007-01-03 22:40:04 +00:00
parent d3db2bd80c
commit 0b29676aa6
1 changed files with 94 additions and 56 deletions
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150
src/backend/utils/adt/selfuncs.c
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@@ -15,7 +15,7 @@
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/utils/adt/selfuncs.c,v 1.119.2.9 2006/05/21 20:07:11 tgl Exp $
* $Header: /cvsroot/pgsql/src/backend/utils/adt/selfuncs.c,v 1.119.2.10 2007/01/03 22:40:04 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -2735,7 +2735,10 @@ get_join_vars(List *args, Var **var1, Var **var2)
* These routines support analysis of LIKE and regular-expression patterns
* by the planner/optimizer. It's important that they agree with the
* regular-expression code in backend/regex/ and the LIKE code in
* backend/utils/adt/like.c.
* backend/utils/adt/like.c. Also, the computation of the fixed prefix
* must be conservative: if we report a string longer than the true fixed
* prefix, the query may produce actually wrong answers, rather than just
* getting a bad selectivity estimate!
*
* Note that the prefix-analysis functions are called from
* backend/optimizer/path/indxpath.c as well as from routines in this file.
@@ -2764,6 +2767,7 @@ like_fixed_prefix(Const *patt_const, bool case_insensitive,
Oid typeid = patt_const->consttype;
int pos,
match_pos;
bool is_multibyte = (pg_database_encoding_max_length() > 1);
/* the right-hand const is type text or bytea */
Assert(typeid == BYTEAOID || typeid == TEXTOID);
@@ -2811,11 +2815,16 @@ like_fixed_prefix(Const *patt_const, bool case_insensitive,
}
/*
* XXX I suspect isalpha() is not an adequately locale-sensitive
* test for characters that can vary under case folding?
* XXX In multibyte character sets, we can't trust isalpha, so assume
* any multibyte char is potentially case-varying.
*/
if (case_insensitive && isalpha((unsigned char) patt[pos]))
break;
if (case_insensitive)
{
if (is_multibyte && (unsigned char) patt[pos] >= 0x80)
break;
if (isalpha((unsigned char) patt[pos]))
break;
}
/*
* NOTE: this code used to think that %% meant a literal %, but
@@ -2861,11 +2870,13 @@ regex_fixed_prefix(Const *patt_const, bool case_insensitive,
char *match;
int pos,
match_pos,
paren_depth;
prev_pos,
prev_match_pos;
bool have_leading_paren;
char *patt;
char *prefix;
char *rest;
Oid typeid = patt_const->consttype;
bool is_multibyte = (pg_database_encoding_max_length() > 1);
/*
* Should be unnecessary, there are no bytea regex operators defined.
@@ -2879,7 +2890,25 @@ regex_fixed_prefix(Const *patt_const, bool case_insensitive,
patt = DatumGetCString(DirectFunctionCall1(textout, patt_const->constvalue));
/* Pattern must be anchored left */
if (patt[0] != '^')
pos = 0;
if (patt[pos] != '^')
{
rest = patt;
*prefix_const = NULL;
*rest_const = string_to_const(rest, typeid);
return Pattern_Prefix_None;
}
pos++;
/*
* If '|' is present in pattern, then there may be multiple alternatives
* for the start of the string. (There are cases where this isn't so,
* for instance if the '|' is inside parens, but detecting that reliably
* is too hard.)
*/
if (strchr(patt + pos, '|') != NULL)
{
rest = patt;
@@ -2889,103 +2918,112 @@ regex_fixed_prefix(Const *patt_const, bool case_insensitive,
return Pattern_Prefix_None;
}
/* OK, allocate space for pattern */
match = palloc(strlen(patt) + 1);
prev_match_pos = match_pos = 0;
/*
* If unquoted | is present at paren level 0 in pattern, then there
* are multiple alternatives for the start of the string.
* We special-case the syntax '^(...)$' because psql uses it. But beware:
* sequences beginning "(?" are not what they seem.
*/
paren_depth = 0;
for (pos = 1; patt[pos]; pos++)
have_leading_paren = false;
if (patt[pos] == '(' && patt[pos + 1] != '?')
{
if (patt[pos] == '|' && paren_depth == 0)
{
rest = patt;
*prefix_const = NULL;
*rest_const = string_to_const(rest, typeid);
return Pattern_Prefix_None;
}
else if (patt[pos] == '(')
paren_depth++;
else if (patt[pos] == ')' && paren_depth > 0)
paren_depth--;
else if (patt[pos] == '\\')
{
/* backslash quotes the next character */
pos++;
if (patt[pos] == '\0')
break;
}
have_leading_paren = true;
pos++;
}
/* OK, allocate space for pattern */
prefix = match = palloc(strlen(patt) + 1);
match_pos = 0;
/* note start at pos 1 to skip leading ^ */
for (pos = 1; patt[pos]; pos++)
/* Scan remainder of pattern */
prev_pos = pos;
while (patt[pos])
{
int len;
/*
* Check for characters that indicate multiple possible matches
* here. XXX I suspect isalpha() is not an adequately
* locale-sensitive test for characters that can vary under case
* folding?
* Check for characters that indicate multiple possible matches here.
* Also, drop out at ')' or '$' so the termination test works right.
*/
if (patt[pos] == '.' ||
patt[pos] == '(' ||
patt[pos] == ')' ||
patt[pos] == '[' ||
patt[pos] == '$' ||
(case_insensitive && isalpha((unsigned char) patt[pos])))
patt[pos] == '^' ||
patt[pos] == '$')
break;
/*
* XXX In multibyte character sets, we can't trust isalpha, so assume
* any multibyte char is potentially case-varying.
*/
if (case_insensitive)
{
if (is_multibyte && (unsigned char) patt[pos] >= 0x80)
break;
if (isalpha((unsigned char) patt[pos]))
break;
}
/*
* Check for quantifiers. Except for +, this means the preceding
* character is optional, so we must remove it from the prefix
* too!
* character is optional, so we must remove it from the prefix too!
*/
if (patt[pos] == '*' ||
patt[pos] == '?' ||
patt[pos] == '{')
{
if (match_pos > 0)
match_pos--;
pos--;
match_pos = prev_match_pos;
pos = prev_pos;
break;
}
if (patt[pos] == '+')
{
pos--;
pos = prev_pos;
break;
}
/*
* backslash quotes the next character.
*/
if (patt[pos] == '\\')
{
/* backslash quotes the next character */
pos++;
if (patt[pos] == '\0')
break;
}
match[match_pos++] = patt[pos];
/* save position in case we need to back up on next loop cycle */
prev_match_pos = match_pos;
prev_pos = pos;
/* must use encoding-aware processing here */
len = pg_mblen(&patt[pos]);
memcpy(&match[match_pos], &patt[pos], len);
match_pos += len;
pos += len;
}
match[match_pos] = '\0';
rest = &patt[pos];
if (have_leading_paren && patt[pos] == ')')
pos++;
if (patt[pos] == '$' && patt[pos + 1] == '\0')
{
rest = &patt[pos + 1];
*prefix_const = string_to_const(prefix, typeid);
*prefix_const = string_to_const(match, typeid);
*rest_const = string_to_const(rest, typeid);
pfree(patt);
pfree(match);
return Pattern_Prefix_Exact; /* pattern specifies exact match */
}
*prefix_const = string_to_const(prefix, typeid);
*prefix_const = string_to_const(match, typeid);
*rest_const = string_to_const(rest, typeid);
pfree(patt);
pfree(match);
prefix = NULL;
if (match_pos > 0)
return Pattern_Prefix_Partial;