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Fix a performance problem in queries that use "ORDER BY rowid DESC" and one or more FTS auxiliary functions.

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FossilOrigin-Name: 95e09b20e9aad28f829c8950f3632debe473070a
This commit is contained in:
dan
2011-05-04 15:41:18 +00:00
parent 0f599faa29
commit e1c8e13bf6
4 changed files with 50 additions and 14 deletions
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47
ext/fts3/fts3.c
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@ -3321,6 +3321,25 @@ int sqlite3Fts3ExprLoadFtDoclist(
return rc;
}
/*
** When called, *ppPoslist must point to the byte immediately following the
** end of a position-list. i.e. ( (*ppPoslist)[-1]==POS_END ). This function
** moves *ppPoslist so that it instead points to the first byte of the
** position list.
*/
static void fts3ReversePoslist(char *pStart, char **ppPoslist){
char *p = &(*ppPoslist)[-3];
char c = p[1];
while( p>=pStart && (*p & 0x80) | c ){
c = *p--;
}
if( p>pStart ){ p = &p[2]; }
while( *p++&0x80 );
*ppPoslist = p;
}
/*
** After ExprLoadDoclist() (see above) has been called, this function is
** used to iterate/search through the position lists that make up the doclist
@ -3337,21 +3356,37 @@ char *sqlite3Fts3FindPositions(
char *pEnd = &pExpr->aDoclist[pExpr->nDoclist];
char *pCsr;
if( pExpr->pCurrent==0 || pCursor->desc ){
pExpr->pCurrent = pExpr->aDoclist;
pExpr->iCurrent = 0;
pExpr->pCurrent += sqlite3Fts3GetVarint(pExpr->pCurrent,&pExpr->iCurrent);
if( pExpr->pCurrent==0 ){
if( pCursor->desc==0 ){
pExpr->pCurrent = pExpr->aDoclist;
pExpr->iCurrent = 0;
fts3GetDeltaVarint(&pExpr->pCurrent, &pExpr->iCurrent);
}else{
pCsr = pExpr->aDoclist;
while( pCsr<pEnd ){
fts3GetDeltaVarint(&pCsr, &pExpr->iCurrent);
fts3PoslistCopy(0, &pCsr);
}
fts3ReversePoslist(pExpr->aDoclist, &pCsr);
pExpr->pCurrent = pCsr;
}
}
pCsr = pExpr->pCurrent;
assert( pCsr );
while( pCsr<pEnd ){
if( pExpr->iCurrent<iDocid ){
while( (pCursor->desc==0 && pCsr<pEnd)
|| (pCursor->desc && pCsr>pExpr->aDoclist)
){
if( pCursor->desc==0 && pExpr->iCurrent<iDocid ){
fts3PoslistCopy(0, &pCsr);
if( pCsr<pEnd ){
fts3GetDeltaVarint(&pCsr, &pExpr->iCurrent);
}
pExpr->pCurrent = pCsr;
}else if( pCursor->desc && pExpr->iCurrent>iDocid ){
fts3GetReverseDeltaVarint(&pCsr, pExpr->aDoclist, &pExpr->iCurrent);
fts3ReversePoslist(pExpr->aDoclist, &pCsr);
pExpr->pCurrent = pCsr;
}else{
if( pExpr->iCurrent==iDocid ){
int iThis = 0;