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Take the LIMIT clause into account when estimating the cost of sorting.

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FossilOrigin-Name: d491745cab951e0de70f1f79b7640ea8aff6e8bb
This commit is contained in:
drh
2016-02-25 16:04:59 +00:00
parent d8c22ac655
commit c3489bbf77
7 changed files with 93 additions and 59 deletions
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35
src/select.c
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@@ -105,7 +105,7 @@ Select *sqlite3SelectNew(
ExprList *pGroupBy, /* the GROUP BY clause */
Expr *pHaving, /* the HAVING clause */
ExprList *pOrderBy, /* the ORDER BY clause */
u16 selFlags, /* Flag parameters, such as SF_Distinct */
u32 selFlags, /* Flag parameters, such as SF_Distinct */
Expr *pLimit, /* LIMIT value. NULL means not used */
Expr *pOffset /* OFFSET value. NULL means no offset */
){
@@ -1845,8 +1845,9 @@ static void computeLimitRegisters(Parse *pParse, Select *p, int iBreak){
VdbeComment((v, "LIMIT counter"));
if( n==0 ){
sqlite3VdbeGoto(v, iBreak);
}else if( n>=0 && p->nSelectRow>(u64)n ){
p->nSelectRow = n;
}else if( n>=0 && p->nSelectRow>sqlite3LogEst((u64)n) ){
p->nSelectRow = sqlite3LogEst((u64)n);
p->selFlags |= SF_FixedLimit;
}
}else{
sqlite3ExprCode(pParse, p->pLimit, iLimit);
@@ -2287,12 +2288,12 @@ static int multiSelect(
testcase( rc!=SQLITE_OK );
pDelete = p->pPrior;
p->pPrior = pPrior;
p->nSelectRow += pPrior->nSelectRow;
p->nSelectRow = sqlite3LogEstAdd(p->nSelectRow, pPrior->nSelectRow);
if( pPrior->pLimit
&& sqlite3ExprIsInteger(pPrior->pLimit, &nLimit)
&& nLimit>0 && p->nSelectRow > (u64)nLimit
&& nLimit>0 && p->nSelectRow > sqlite3LogEst((u64)nLimit)
){
p->nSelectRow = nLimit;
p->nSelectRow = sqlite3LogEst((u64)nLimit);
}
if( addr ){
sqlite3VdbeJumpHere(v, addr);
@@ -2364,7 +2365,9 @@ static int multiSelect(
pDelete = p->pPrior;
p->pPrior = pPrior;
p->pOrderBy = 0;
if( p->op==TK_UNION ) p->nSelectRow += pPrior->nSelectRow;
if( p->op==TK_UNION ){
p->nSelectRow = sqlite3LogEstAdd(p->nSelectRow, pPrior->nSelectRow);
}
sqlite3ExprDelete(db, p->pLimit);
p->pLimit = pLimit;
p->pOffset = pOffset;
@@ -3001,7 +3004,7 @@ static int multiSelectOrderBy(
addrEofA_noB = sqlite3VdbeAddOp2(v, OP_Yield, regAddrB, labelEnd);
VdbeCoverage(v);
sqlite3VdbeGoto(v, addrEofA);
p->nSelectRow += pPrior->nSelectRow;
p->nSelectRow = sqlite3LogEstAdd(p->nSelectRow, pPrior->nSelectRow);
}
/* Generate a subroutine to run when the results from select B
@@ -4987,7 +4990,7 @@ int sqlite3Select(
sqlite3SelectDestInit(&dest, SRT_Coroutine, pItem->regReturn);
explainSetInteger(pItem->iSelectId, (u8)pParse->iNextSelectId);
sqlite3Select(pParse, pSub, &dest);
pItem->pTab->nRowLogEst = sqlite3LogEst(pSub->nSelectRow);
pItem->pTab->nRowLogEst = pSub->nSelectRow;
pItem->fg.viaCoroutine = 1;
pItem->regResult = dest.iSdst;
sqlite3VdbeEndCoroutine(v, pItem->regReturn);
@@ -5018,7 +5021,7 @@ int sqlite3Select(
sqlite3SelectDestInit(&dest, SRT_EphemTab, pItem->iCursor);
explainSetInteger(pItem->iSelectId, (u8)pParse->iNextSelectId);
sqlite3Select(pParse, pSub, &dest);
pItem->pTab->nRowLogEst = sqlite3LogEst(pSub->nSelectRow);
pItem->pTab->nRowLogEst = pSub->nSelectRow;
if( onceAddr ) sqlite3VdbeJumpHere(v, onceAddr);
retAddr = sqlite3VdbeAddOp1(v, OP_Return, pItem->regReturn);
VdbeComment((v, "end %s", pItem->pTab->zName));
@@ -5101,7 +5104,7 @@ int sqlite3Select(
/* Set the limiter.
*/
iEnd = sqlite3VdbeMakeLabel(v);
p->nSelectRow = LARGEST_INT64;
p->nSelectRow = 320; /* 4 billion rows */
computeLimitRegisters(pParse, p, iEnd);
if( p->iLimit==0 && sSort.addrSortIndex>=0 ){
sqlite3VdbeChangeOpcode(v, sSort.addrSortIndex, OP_SorterOpen);
@@ -5125,10 +5128,12 @@ int sqlite3Select(
if( !isAgg && pGroupBy==0 ){
/* No aggregate functions and no GROUP BY clause */
u16 wctrlFlags = (sDistinct.isTnct ? WHERE_WANT_DISTINCT : 0);
assert( WHERE_USE_LIMIT==SF_FixedLimit );
wctrlFlags |= p->selFlags & SF_FixedLimit;
/* Begin the database scan. */
pWInfo = sqlite3WhereBegin(pParse, pTabList, pWhere, sSort.pOrderBy,
p->pEList, wctrlFlags, 0);
p->pEList, wctrlFlags, p->nSelectRow);
if( pWInfo==0 ) goto select_end;
if( sqlite3WhereOutputRowCount(pWInfo) < p->nSelectRow ){
p->nSelectRow = sqlite3WhereOutputRowCount(pWInfo);
@@ -5188,9 +5193,11 @@ int sqlite3Select(
for(k=pGroupBy->nExpr, pItem=pGroupBy->a; k>0; k--, pItem++){
pItem->u.x.iAlias = 0;
}
if( p->nSelectRow>100 ) p->nSelectRow = 100;
assert( 66==sqlite3LogEst(100) );
if( p->nSelectRow>66 ) p->nSelectRow = 66;
}else{
p->nSelectRow = 1;
assert( 0==sqlite3LogEst(1) );
p->nSelectRow = 0;
}
/* If there is both a GROUP BY and an ORDER BY clause and they are