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Avoid unnecessary copying of source string when generating a cloned TParser.

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For long source strings the copying results in O(N^2) behavior, and the
multiplier can be significant if wide-char conversion is involved.

Andres Freund, reviewed by Kevin Grittner.
This commit is contained in:
Tom Lane 2009-12-15 20:37:17 +00:00
parent a5495cd841
commit 21d11e7ee2
1 changed files with 69 additions and 5 deletions
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74
src/backend/tsearch/wparser_def.c
View File

@ -7,7 +7,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/tsearch/wparser_def.c,v 1.25 2009/11/15 13:57:01 petere Exp $
* $PostgreSQL: pgsql/src/backend/tsearch/wparser_def.c,v 1.26 2009/12/15 20:37:17 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -328,6 +328,46 @@ TParserInit(char *str, int len)
return prs;
}
/*
* As an alternative to a full TParserInit one can create a
* TParserCopy which basically is a regular TParser without a private
* copy of the string - instead it uses the one from another TParser.
* This is useful because at some places TParsers are created
* recursively and the repeated copying around of the strings can
* cause major inefficiency if the source string is long.
* The new parser starts parsing at the original's current position.
*
* Obviously one must not close the original TParser before the copy.
*/
static TParser *
TParserCopyInit(const TParser *orig)
{
TParser *prs = (TParser *) palloc0(sizeof(TParser));
prs->charmaxlen = orig->charmaxlen;
prs->str = orig->str + orig->state->posbyte;
prs->lenstr = orig->lenstr - orig->state->posbyte;
#ifdef USE_WIDE_UPPER_LOWER
prs->usewide = orig->usewide;
if (orig->pgwstr)
prs->pgwstr = orig->pgwstr + orig->state->poschar;
if (orig->wstr)
prs->wstr = orig->wstr + orig->state->poschar;
#endif
prs->state = newTParserPosition(NULL);
prs->state->state = TPS_Base;
#ifdef WPARSER_TRACE
fprintf(stderr, "parsing copy of \"%.*s\"\n", prs->lenstr, prs->str);
#endif
return prs;
}
static void
TParserClose(TParser *prs)
{
@ -346,9 +386,33 @@ TParserClose(TParser *prs)
pfree(prs->pgwstr);
#endif
#ifdef WPARSER_TRACE
fprintf(stderr, "closing parser");
#endif
pfree(prs);
}
/*
* Close a parser created with TParserCopyInit
*/
static void
TParserCopyClose(TParser *prs)
{
while (prs->state)
{
TParserPosition *ptr = prs->state->prev;
pfree(prs->state);
prs->state = ptr;
}
#ifdef WPARSER_TRACE
fprintf(stderr, "closing parser copy");
#endif
pfree(prs);
}
/*
* Character-type support functions, equivalent to is* macros, but
* working with any possible encodings and locales. Notes:
@ -617,7 +681,7 @@ p_isignore(TParser *prs)
static int
p_ishost(TParser *prs)
{
TParser *tmpprs = TParserInit(prs->str + prs->state->posbyte, prs->lenstr - prs->state->posbyte);
TParser *tmpprs = TParserCopyInit(prs);
int res = 0;
tmpprs->wanthost = true;
@ -631,7 +695,7 @@ p_ishost(TParser *prs)
prs->state->charlen = tmpprs->state->charlen;
res = 1;
}
TParserClose(tmpprs);
TParserCopyClose(tmpprs);
return res;
}
@ -639,7 +703,7 @@ p_ishost(TParser *prs)
static int
p_isURLPath(TParser *prs)
{
TParser *tmpprs = TParserInit(prs->str + prs->state->posbyte, prs->lenstr - prs->state->posbyte);
TParser *tmpprs = TParserCopyInit(prs);
int res = 0;
tmpprs->state = newTParserPosition(tmpprs->state);
@ -654,7 +718,7 @@ p_isURLPath(TParser *prs)
prs->state->charlen = tmpprs->state->charlen;
res = 1;
}
TParserClose(tmpprs);
TParserCopyClose(tmpprs);
return res;
}