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Fix multiple issues with the ORDER BY LIMIT optimization. This is the

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proposed resolution to ticket [9936b2fa443fec03ff25].

FossilOrigin-Name: 206720129ed2fa8875a286266d05b99fb2caf8671e4b74b26a6286a2073fcd8b
This commit is contained in:
drh
2018-09-08 20:09:46 +00:00
parent c93c614543
commit 6ee5a7b481
6 changed files with 97 additions and 27 deletions
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38
src/where.c
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@@ -67,15 +67,38 @@ int sqlite3WhereIsOrdered(WhereInfo *pWInfo){
}
/*
** Return TRUE if the innermost loop of the WHERE clause implementation
** returns rows in ORDER BY order for complete run of the inner loop.
** In the ORDER BY LIMIT optimization, if the inner-most loop is known
** to emit rows in increasing order, and if the last row emitted by the
** inner-most loop did not fit within the sorter, then we can skip all
** subsequent rows for the current iteration of the inner loop (because they
** will not fit in the sorter either) and continue with the second inner
** loop - the loop immediately outside the inner-most.
**
** Across multiple iterations of outer loops, the output rows need not be
** sorted. As long as rows are sorted for just the innermost loop, this
** routine can return TRUE.
** When a row does not fit in the sorter (because the sorter already
** holds LIMIT+OFFSET rows that are smaller), then a jump is made to the
** label returned by this function.
**
** If the ORDER BY LIMIT optimization applies, the jump destination should
** be the continuation for the second-inner-most loop. If the ORDER BY
** LIMIT optimization does not apply, then the jump destination should
** be the continuation for the inner-most loop.
**
** It is always safe for this routine to return the continuation of the
** inner-most loop, in the sense that a correct answer will result.
** Returning the continuation the second inner loop is an optimization
** that might make the code run a little faster, but should not change
** the final answer.
*/
int sqlite3WhereOrderedInnerLoop(WhereInfo *pWInfo){
return pWInfo->bOrderedInnerLoop;
int sqlite3WhereOrderByLimitOptLabel(WhereInfo *pWInfo){
WhereLevel *pInner;
if( !pWInfo->bOrderedInnerLoop ){
/* The ORDER BY LIMIT optimization does not apply. Jump to the
** continuation of the inner-most loop. */
return pWInfo->iContinue;
}
pInner = &pWInfo->a[pWInfo->nLevel-1];
if( pInner->addrNxt ) return pInner->addrNxt;
return pInner->addrBrk;
}
/*
@@ -4248,6 +4271,7 @@ static int wherePathSolver(WhereInfo *pWInfo, LogEst nRowEst){
pWInfo->eDistinct = WHERE_DISTINCT_ORDERED;
}
}
pWInfo->bOrderedInnerLoop = 0;
if( pWInfo->pOrderBy ){
if( pWInfo->wctrlFlags & WHERE_DISTINCTBY ){
if( pFrom->isOrdered==pWInfo->pOrderBy->nExpr ){