WherePlan plan; /* The lookup strategy */
double rCost; /* Overall cost of pursuing this search strategy */
double nRow; /* Estimated number of output rows */
+ Bitmask used; /* Bitmask of cursors used by this plan */
};
/*
nTerm = pOrderBy->nExpr;
assert( nTerm>0 );
+ /* Argument pIdx must either point to a 'real' named index structure,
+ ** or an index structure allocated on the stack by bestBtreeIndex() to
+ ** represent the rowid index that is part of every table. */
+ assert( pIdx->zName || (pIdx->nColumn==1 && pIdx->aiColumn[0]==-1) );
+
/* Match terms of the ORDER BY clause against columns of
** the index.
**
if( !pColl ){
pColl = db->pDfltColl;
}
- if( i<pIdx->nColumn ){
+ if(
pIdx->zName && i<pIdx->nColumn ){
iColumn = pIdx->aiColumn[i];
if( iColumn==pIdx->pTable->iPKey ){
iColumn = -1;
return 0;
}
}
- assert( pIdx->aSortOrder!=0 );
+ assert( pIdx->aSortOrder!=0 || iColumn==-1 );
assert( pTerm->sortOrder==0 || pTerm->sortOrder==1 );
assert( iSortOrder==0 || iSortOrder==1 );
termSortOrder = iSortOrder ^ pTerm->sortOrder;
return 0;
}
-/*
-** Check table to see if the ORDER BY clause in pOrderBy can be satisfied
-** by sorting in order of ROWID. Return true if so and set *pbRev to be
-** true for reverse ROWID and false for forward ROWID order.
-*/
-static int sortableByRowid(
- int base, /* Cursor number for table to be sorted */
- ExprList *pOrderBy, /* The ORDER BY clause */
- WhereMaskSet *pMaskSet, /* Mapping from table cursors to bitmaps */
- int *pbRev /* Set to 1 if ORDER BY is DESC */
-){
- Expr *p;
-
- assert( pOrderBy!=0 );
- assert( pOrderBy->nExpr>0 );
- p = pOrderBy->a[0].pExpr;
- if( p->op==TK_COLUMN && p->iTable==base && p->iColumn==-1
- && !referencesOtherTables(pOrderBy, pMaskSet, 1, base) ){
- *pbRev = pOrderBy->a[0].sortOrder;
- return 1;
- }
- return 0;
-}
-
/*
** Prepare a crude estimate of the logarithm of the input value.
** The results need not be exact. This is only used for estimating
int flags = WHERE_MULTI_OR;
double rTotal = 0;
double nRow = 0;
+ Bitmask used = 0;
for(pOrTerm=pOrWC->a; pOrTerm<pOrWCEnd; pOrTerm++){
WhereCost sTermCost;
}
rTotal += sTermCost.rCost;
nRow += sTermCost.nRow;
+ used |= sTermCost.used;
if( rTotal>=pCost->rCost ) break;
}
if( rTotal<pCost->rCost ){
pCost->rCost = rTotal;
pCost->nRow = nRow;
+ pCost->used = used;
pCost->plan.wsFlags = flags;
pCost->plan.u.pTerm = pTerm;
}
for(i=0; i<pIdxInfo->nConstraint; i++, pIdxCons++){
j = pIdxCons->iTermOffset;
pTerm = &pWC->a[j];
- pIdxCons->usable = (pTerm->prereqRight & notReady)==0 ?1:0;
+ pIdxCons->usable = (pTerm->prereqRight¬Ready) ? 0 : 1;
}
memset(pUsage, 0, sizeof(pUsage[0])*pIdxInfo->nConstraint);
if( pIdxInfo->needToFreeIdxStr ){
return;
}
+ pIdxCons = *(struct sqlite3_index_constraint**)&pIdxInfo->aConstraint;
+ for(i=0; i<pIdxInfo->nConstraint; i++){
+ if( pUsage[i].argvIndex>0 ){
+ pCost->used |= pWC->a[pIdxCons[i].iTermOffset].prereqRight;
+ }
+ }
+
/* The cost is not allowed to be larger than SQLITE_BIG_DBL (the
** inital value of lowestCost in this loop. If it is, then the
** (cost<lowestCost) test below will never be true.
ExprList *pOrderBy, /* The ORDER BY clause */
WhereCost *pCost /* Lowest cost query plan */
){
- WhereTerm *pTerm; /* A single term of the WHERE clause */
int iCur = pSrc->iCursor; /* The cursor of the table to be accessed */
Index *pProbe; /* An index we are evaluating */
- int rev; /* True to scan in reverse order */
- int wsFlags; /* Flags associated with pProbe */
- int nEq; /* Number of == or IN constraints */
- int eqTermMask; /* Mask of valid equality operators */
- double cost; /* Cost of using pProbe */
- double nRow; /* Estimated number of rows in result set */
- int i; /* Loop counter */
-
- WHERETRACE(("bestIndex: tbl=%s notReady=%llx\n", pSrc->pTab->zName,notReady));
- pProbe = pSrc->pTab->pIndex;
- if( pSrc->notIndexed ){
- pProbe = 0;
- }
-
- /* If the table has no indices and there are no terms in the where
- ** clause that refer to the ROWID, then we will never be able to do
- ** anything other than a full table scan on this table. We might as
- ** well put it first in the join order. That way, perhaps it can be
- ** referenced by other tables in the join.
- */
- memset(pCost, 0, sizeof(*pCost));
- if( pProbe==0 &&
- findTerm(pWC, iCur, -1, 0, WO_EQ|WO_IN|WO_LT|WO_LE|WO_GT|WO_GE,0)==0 &&
- (pOrderBy==0 || !sortableByRowid(iCur, pOrderBy, pWC->pMaskSet, &rev)) ){
- if( pParse->db->flags & SQLITE_ReverseOrder ){
- /* For application testing, randomly reverse the output order for
- ** SELECT statements that omit the ORDER BY clause. This will help
- ** to find cases where
- */
- pCost->plan.wsFlags |= WHERE_REVERSE;
- }
- return;
- }
- pCost->rCost = SQLITE_BIG_DBL;
+ Index *pIdx; /* Copy of pProbe, or zero for IPK index */
+ int eqTermMask; /* Current mask of valid equality operators */
+ int idxEqTermMask; /* Index mask of valid equality operators */
- /* Check for a rowid=EXPR or rowid IN (...) constraints. If there was
- ** an INDEXED BY clause attached to this table, skip this step.
- */
- if( !pSrc->pIndex ){
- pTerm = findTerm(pWC, iCur, -1, notReady, WO_EQ|WO_IN, 0);
- if( pTerm ){
- Expr *pExpr;
- pCost->plan.wsFlags = WHERE_ROWID_EQ;
- if( pTerm->eOperator & WO_EQ ){
- /* Rowid== is always the best pick. Look no further. Because only
- ** a single row is generated, output is always in sorted order */
- pCost->plan.wsFlags = WHERE_ROWID_EQ | WHERE_UNIQUE;
- pCost->plan.nEq = 1;
- WHERETRACE(("... best is rowid\n"));
- pCost->rCost = 0;
- pCost->nRow = 1;
- return;
- }else if( !ExprHasProperty((pExpr = pTerm->pExpr), EP_xIsSelect)
- && pExpr->x.pList
- ){
- /* Rowid IN (LIST): cost is NlogN where N is the number of list
- ** elements. */
- pCost->rCost = pCost->nRow = pExpr->x.pList->nExpr;
- pCost->rCost *= estLog(pCost->rCost);
- }else{
- /* Rowid IN (SELECT): cost is NlogN where N is the number of rows
- ** in the result of the inner select. We have no way to estimate
- ** that value so make a wild guess. */
- pCost->nRow = 100;
- pCost->rCost = 200;
- }
- WHERETRACE(("... rowid IN cost: %.9g\n", pCost->rCost));
- }
-
- /* Estimate the cost of a table scan. If we do not know how many
- ** entries are in the table, use 1 million as a guess.
- */
- cost = pProbe ? pProbe->aiRowEst[0] : 1000000;
- WHERETRACE(("... table scan base cost: %.9g\n", cost));
- wsFlags = WHERE_ROWID_RANGE;
-
- /* Check for constraints on a range of rowids in a table scan.
- */
- pTerm = findTerm(pWC, iCur, -1, notReady, WO_LT|WO_LE|WO_GT|WO_GE, 0);
- if( pTerm ){
- if( findTerm(pWC, iCur, -1, notReady, WO_LT|WO_LE, 0) ){
- wsFlags |= WHERE_TOP_LIMIT;
- cost /= 3; /* Guess that rowid<EXPR eliminates two-thirds of rows */
- }
- if( findTerm(pWC, iCur, -1, notReady, WO_GT|WO_GE, 0) ){
- wsFlags |= WHERE_BTM_LIMIT;
- cost /= 3; /* Guess that rowid>EXPR eliminates two-thirds of rows */
- }
- WHERETRACE(("... rowid range reduces cost to %.9g\n", cost));
- }else{
- wsFlags = 0;
- }
- nRow = cost;
-
- /* If the table scan does not satisfy the ORDER BY clause, increase
- ** the cost by NlogN to cover the expense of sorting. */
- if( pOrderBy ){
- if( sortableByRowid(iCur, pOrderBy, pWC->pMaskSet, &rev) ){
- wsFlags |= WHERE_ORDERBY|WHERE_ROWID_RANGE;
- if( rev ){
- wsFlags |= WHERE_REVERSE;
- }
- }else{
- cost += cost*estLog(cost);
- WHERETRACE(("... sorting increases cost to %.9g\n", cost));
- }
- }else if( pParse->db->flags & SQLITE_ReverseOrder ){
- /* For application testing, randomly reverse the output order for
- ** SELECT statements that omit the ORDER BY clause. This will help
- ** to find cases where
- */
- wsFlags |= WHERE_REVERSE;
- }
+ Index pk;
+ unsigned int pkint[2] = {1000000, 1};
+ int pkicol = -1;
+ int wsFlagMask;
- /* Remember this case if it is the best so far */
- if( cost<pCost->rCost ){
- pCost->rCost = cost;
- pCost->nRow = nRow;
- pCost->plan.wsFlags = wsFlags;
- }
- }
-
- bestOrClauseIndex(pParse, pWC, pSrc, notReady, pOrderBy, pCost);
+ memset(pCost, 0, sizeof(*pCost));
+ pCost->rCost = SQLITE_BIG_DBL;
/* If the pSrc table is the right table of a LEFT JOIN then we may not
** use an index to satisfy IS NULL constraints on that table. This is
** because columns might end up being NULL if the table does not match -
** a circumstance which the index cannot help us discover. Ticket #2177.
*/
- if( (pSrc->jointype & JT_LEFT)!=0 ){
- eqTermMask = WO_EQ|WO_IN;
+ if( pSrc->jointype & JT_LEFT ){
+ idxEqTermMask = WO_EQ|WO_IN;
}else{
- eqTermMask = WO_EQ|WO_IN|WO_ISNULL;
+ idxEqTermMask = WO_EQ|WO_IN|WO_ISNULL;
}
- /* Look at each index.
- */
if( pSrc->pIndex ){
- pProbe = pSrc->pIndex;
- }
- for(; pProbe; pProbe=(pSrc->pIndex ? 0 : pProbe->pNext)){
- double inMultiplier = 1; /* Number of equality look-ups needed */
- int inMultIsEst = 0; /* True if inMultiplier is an estimate */
-
- WHERETRACE(("... index %s:\n", pProbe->zName));
-
- /* Count the number of columns in the index that are satisfied
- ** by x=EXPR or x IS NULL constraints or x IN (...) constraints.
- ** For a term of the form x=EXPR or x IS NULL we only have to do
- ** a single binary search. But for x IN (...) we have to do a
- ** number of binary searched
- ** equal to the number of entries on the RHS of the IN operator.
- ** The inMultipler variable with try to estimate the number of
- ** binary searches needed.
+ pIdx = pProbe = pSrc->pIndex;
+ wsFlagMask = ~(WHERE_ROWID_EQ|WHERE_ROWID_RANGE);
+ eqTermMask = idxEqTermMask;
+ }else{
+ Index *pFirst = pSrc->pTab->pIndex;
+ memset(&pk, 0, sizeof(Index));
+ pk.nColumn = 1;
+ pk.aiColumn = &pkicol;
+ pk.aiRowEst = pkint;
+ pk.onError = OE_Replace;
+ pk.pTable = pSrc->pTab;
+ if( pSrc->notIndexed==0 ){
+ pk.pNext = pFirst;
+ }
+ if( pFirst && pFirst->aiRowEst ){
+ pkint[0] = pFirst->aiRowEst[0];
+ }
+ pProbe = &pk;
+ wsFlagMask = ~(
+ WHERE_COLUMN_IN|WHERE_COLUMN_EQ|WHERE_COLUMN_NULL|WHERE_COLUMN_RANGE
+ );
+ eqTermMask = WO_EQ|WO_IN;
+ pIdx = 0;
+ }
+
+
+ for(; pProbe; pIdx=pProbe=pProbe->pNext){
+ const unsigned int * const aiRowEst = pProbe->aiRowEst;
+ double cost; /* Cost of using pProbe */
+ double nRow; /* Estimated number of rows in result set */
+ int rev; /* True to scan in reverse order */
+ int wsFlags = 0;
+ Bitmask used = 0;
+
+ /* The following variables are populated based on the properties of
+ ** scan being evaluated. They are then used to determine the expected
+ ** cost and number of rows returned.
+ **
+ ** nEq:
+ ** Number of equality terms that can be implemented using the index.
+ **
+ ** nInMul:
+ ** The "in-multiplier". This is an estimate of how many seek operations
+ ** SQLite must perform on the index in question. For example, if the
+ ** WHERE clause is:
+ **
+ ** WHERE a IN (1, 2, 3) AND b IN (4, 5, 6)
+ **
+ ** SQLite must perform 9 lookups on an index on (a, b), so nInMul is
+ ** set to 9. Given the same schema and either of the following WHERE
+ ** clauses:
+ **
+ ** WHERE a = 1
+ ** WHERE a >= 2
+ **
+ ** nInMul is set to 1.
+ **
+ ** If there exists a WHERE term of the form "x IN (SELECT ...)", then
+ ** the sub-select is assumed to return 25 rows for the purposes of
+ ** determining nInMul.
+ **
+ ** bInEst:
+ ** Set to true if there was at least one "x IN (SELECT ...)" term used
+ ** in determining the value of nInMul.
+ **
+ ** nBound:
+ ** Set based on whether or not there is a range constraint on the
+ ** (nEq+1)th column of the index. 1 if there is neither an upper or
+ ** lower bound, 3 if there is an upper or lower bound, or 9 if there
+ ** is both an upper and lower bound.
+ **
+ ** bSort:
+ ** Boolean. True if there is an ORDER BY clause that will require an
+ ** external sort (i.e. scanning the index being evaluated will not
+ ** correctly order records).
+ **
+ ** bLookup:
+ ** Boolean. True if for each index entry visited a lookup on the
+ ** corresponding table b-tree is required. This is always false
+ ** for the rowid index. For other indexes, it is true unless all the
+ ** columns of the table used by the SELECT statement are present in
+ ** the index (such an index is sometimes described as a covering index).
+ ** For example, given the index on (a, b), the second of the following
+ ** two queries requires table b-tree lookups, but the first does not.
+ **
+ ** SELECT a, b FROM tbl WHERE a = 1;
+ ** SELECT a, b, c FROM tbl WHERE a = 1;
*/
- wsFlags = 0;
- for(i=0; i<pProbe->nColumn; i++){
- int j = pProbe->aiColumn[i];
- pTerm = findTerm(pWC, iCur, j, notReady, eqTermMask, pProbe);
+ int nEq;
+ int bInEst = 0;
+ int nInMul = 1;
+ int nBound = 1;
+ int bSort = 0;
+ int bLookup = 0;
+
+ /* Determine the values of nEq and nInMul */
+ for(nEq=0; nEq<pProbe->nColumn; nEq++){
+ WhereTerm *pTerm; /* A single term of the WHERE clause */
+ int j = pProbe->aiColumn[nEq];
+ pTerm = findTerm(pWC, iCur, j, notReady, eqTermMask, pIdx);
if( pTerm==0 ) break;
- wsFlags |= WHERE_COLUMN_EQ;
+ wsFlags |= (WHERE_COLUMN_EQ|WHERE_ROWID_EQ);
if( pTerm->eOperator & WO_IN ){
Expr *pExpr = pTerm->pExpr;
wsFlags |= WHERE_COLUMN_IN;
if( ExprHasProperty(pExpr, EP_xIsSelect) ){
- inMultiplier *= 25;
- inMultIsEst = 1;
+ nInMul *= 25;
+ bInEst = 1;
}else if( pExpr->x.pList ){
- inMultiplier *= pExpr->x.pList->nExpr + 1;
+ nInMul *= pExpr->x.pList->nExpr + 1;
}
}else if( pTerm->eOperator & WO_ISNULL ){
wsFlags |= WHERE_COLUMN_NULL;
}
+ used |= pTerm->prereqRight;
}
- nRow = pProbe->aiRowEst[i] * inMultiplier;
- /* If inMultiplier is an estimate and that estimate results in an
- ** nRow it that is more than half number of rows in the table,
- ** then reduce inMultipler */
- if( inMultIsEst && nRow*2 > pProbe->aiRowEst[0] ){
- nRow = pProbe->aiRowEst[0]/2;
- inMultiplier = nRow/pProbe->aiRowEst[i];
- }
- cost = nRow + inMultiplier*estLog(pProbe->aiRowEst[0]);
- nEq = i;
- if( pProbe->onError!=OE_None && nEq==pProbe->nColumn ){
- testcase( wsFlags & WHERE_COLUMN_IN );
- testcase( wsFlags & WHERE_COLUMN_NULL );
- if( (wsFlags & (WHERE_COLUMN_IN|WHERE_COLUMN_NULL))==0 ){
- wsFlags |= WHERE_UNIQUE;
- }
- }
- WHERETRACE(("...... nEq=%d inMult=%.9g nRow=%.9g cost=%.9g\n",
- nEq, inMultiplier, nRow, cost));
- /* Look for range constraints. Assume that each range constraint
- ** makes the search space 1/3rd smaller.
- */
+ /* Determine the value of nBound. */
if( nEq<pProbe->nColumn ){
int j = pProbe->aiColumn[nEq];
- pTerm = findTerm(pWC, iCur, j, notReady, WO_LT|WO_LE|WO_GT|WO_GE, pProbe);
- if( pTerm ){
- wsFlags |= WHERE_COLUMN_RANGE;
- if( findTerm(pWC, iCur, j, notReady, WO_LT|WO_LE, pProbe) ){
+ if( findTerm(pWC, iCur, j, notReady, WO_LT|WO_LE|WO_GT|WO_GE, pIdx) ){
+ WhereTerm *pTop = findTerm(pWC, iCur, j, notReady, WO_LT|WO_LE, pIdx);
+ WhereTerm *pBtm = findTerm(pWC, iCur, j, notReady, WO_GT|WO_GE, pIdx);
+ if( pTop ){
wsFlags |= WHERE_TOP_LIMIT;
- cost /= 3;
- nRow /= 3;
+ nBound *= 3;
+ used |= pTop->prereqRight;
}
- if( findTerm(pWC, iCur, j, notReady, WO_GT|WO_GE, pProbe) ){
+ if( pBtm ){
wsFlags |= WHERE_BTM_LIMIT;
- cost /= 3;
- nRow /= 3;
+ nBound *= 3;
+ used |= pBtm->prereqRight;
}
- WHERETRACE(("...... range reduces nRow to %.9g and cost to %.9g\n",
- nRow, cost));
+ wsFlags |= (WHERE_COLUMN_RANGE|WHERE_ROWID_RANGE);
+ }
+ }else if( pProbe->onError!=OE_None ){
+ testcase( wsFlags & WHERE_COLUMN_IN );
+ testcase( wsFlags & WHERE_COLUMN_NULL );
+ if( (wsFlags & (WHERE_COLUMN_IN|WHERE_COLUMN_NULL))==0 ){
+ wsFlags |= WHERE_UNIQUE;
}
}
- /* Add the additional cost of sorting if that is a factor.
- */
+ /* If there is an ORDER BY clause and the index being considered will
+ ** naturally scan rows in the required order, set the appropriate flags
+ ** in wsFlags. Otherwise, if there is an ORDER BY clause but the index
+ ** will scan rows in a different order, set the bSort variable. */
if( pOrderBy ){
if( (wsFlags & (WHERE_COLUMN_IN|WHERE_COLUMN_NULL))==0
- && isSortingIndex(pParse,pWC->pMaskSet,pProbe,iCur,pOrderBy,nEq,&rev)
+ && isSortingIndex(pParse,pWC->pMaskSet,pProbe,iCur,pOrderBy,nEq,&rev)
){
- if( wsFlags==0 ){
- wsFlags = WHERE_COLUMN_RANGE;
- }
- wsFlags |= WHERE_ORDERBY;
- if( rev ){
- wsFlags |= WHERE_REVERSE;
- }
+ wsFlags |= WHERE_ROWID_RANGE|WHERE_COLUMN_RANGE|WHERE_ORDERBY;
+ wsFlags |= (rev ? WHERE_REVERSE : 0);
}else{
- cost += cost*estLog(cost);
- WHERETRACE(("...... orderby increases cost to %.9g\n", cost));
+ bSort = 1;
}
- }else if( wsFlags!=0 && (pParse->db->flags & SQLITE_ReverseOrder)!=0 ){
- /* For application testing, randomly reverse the output order for
- ** SELECT statements that omit the ORDER BY clause. This will help
- ** to find cases where
- */
- wsFlags |= WHERE_REVERSE;
}
- /* Check to see if we can get away with using just the index without
- ** ever reading the table. If that is the case, then halve the
- ** cost of this index.
- */
- if( wsFlags && pSrc->colUsed < (((Bitmask)1)<<(BMS-1)) ){
+ /* If currently calculating the cost of using an index (not the IPK
+ ** index), determine if all required column data may be obtained without
+ ** seeking to entries in the main table (i.e. if the index is a covering
+ ** index for this query). If it is, set the WHERE_IDX_ONLY flag in
+ ** wsFlags. Otherwise, set the bLookup variable to true. */
+ if( pIdx && wsFlags ){
Bitmask m = pSrc->colUsed;
int j;
- for(j=0; j<pProbe->nColumn; j++){
- int x = pProbe->aiColumn[j];
+ for(j=0; j<pIdx->nColumn; j++){
+ int x = pIdx->aiColumn[j];
if( x<BMS-1 ){
m &= ~(((Bitmask)1)<<x);
}
}
if( m==0 ){
wsFlags |= WHERE_IDX_ONLY;
- cost /= 2;
- WHERETRACE(("...... idx-only reduces cost to %.9g\n", cost));
+ }else{
+ bLookup = 1;
}
}
- /* If this index has achieved the lowest cost so far, then use it.
- */
- if( wsFlags!=0 && cost < pCost->rCost ){
+#if 0
+ if( bInEst && (nInMul*aiRowEst[nEq])>(aiRowEst[0]/2) ){
+ nInMul = aiRowEst[0] / (2 * aiRowEst[nEq]);
+ }
+ nRow = (double)(aiRowEst[nEq] * nInMul) / nBound;
+ cost = (nEq>0) * nInMul * estLog(aiRowEst[0])
+ + nRow
+ + bSort * nRow * estLog(nRow)
+ + bLookup * nRow * estLog(aiRowEst[0]);
+#else
+
+ /* The following block calculates nRow and cost for the index scan
+ ** in the same way as SQLite versions 3.6.17 and earlier. Some elements
+ ** of this calculation are difficult to justify. But using this strategy
+ ** works well in practice and causes the test suite to pass. */
+ nRow = (double)(aiRowEst[nEq] * nInMul);
+ if( bInEst && nRow*2>aiRowEst[0] ){
+ nRow = aiRowEst[0]/2;
+ nInMul = nRow / aiRowEst[nEq];
+ }
+ cost = nRow + nInMul*estLog(aiRowEst[0]);
+ nRow /= nBound;
+ cost /= nBound;
+ if( bSort ){
+ cost += cost*estLog(cost);
+ }
+ if( pIdx && bLookup==0 ){
+ cost /= 2;
+ }
+#endif
+
+ WHERETRACE((
+ "tbl=%s idx=%s nEq=%d nInMul=%d nBound=%d bSort=%d bLookup=%d"
+ " wsFlags=%d (nRow=%.2f cost=%.2f)\n",
+ pSrc->pTab->zName, (pIdx ? pIdx->zName : "ipk"),
+ nEq, nInMul, nBound, bSort, bLookup, wsFlags, nRow, cost
+ ));
+
+ if( (!pIdx || wsFlags) && cost<pCost->rCost ){
pCost->rCost = cost;
pCost->nRow = nRow;
- pCost->plan.wsFlags = wsFlags;
+ pCost->used = used;
+ pCost->plan.wsFlags = (wsFlags&wsFlagMask);
pCost->plan.nEq = nEq;
- assert( pCost->plan.wsFlags & WHERE_INDEXED );
- pCost->plan.u.pIdx = pProbe;
+ pCost->plan.u.pIdx = pIdx;
}
+
+ if( pSrc->pIndex ) break;
+ wsFlagMask = ~(WHERE_ROWID_EQ|WHERE_ROWID_RANGE);
+ eqTermMask = idxEqTermMask;
}
- /* Report the best result
- */
+ /* If there is no ORDER BY clause and the SQLITE_ReverseOrder flag
+ ** is set, then reverse the order that the index will be scanned
+ ** in. This is used for application testing, to help find cases
+ ** where application behaviour depends on the (undefined) order that
+ ** SQLite outputs rows in in the absence of an ORDER BY clause. */
+ if( !pOrderBy && pParse->db->flags & SQLITE_ReverseOrder ){
+ pCost->plan.wsFlags |= WHERE_REVERSE;
+ }
+
+ assert( pOrderBy || (pCost->plan.wsFlags&WHERE_ORDERBY)==0 );
+ assert( pCost->plan.u.pIdx==0 || (pCost->plan.wsFlags&WHERE_ROWID_EQ)==0 );
+ assert( pSrc->pIndex==0
+ || pCost->plan.u.pIdx==0
+ || pCost->plan.u.pIdx==pSrc->pIndex
+ );
+
+ WHERETRACE(("best index is: %s\n",
+ (pCost->plan.u.pIdx ? pCost->plan.u.pIdx->zName : "ipk")
+ ));
+
+ bestOrClauseIndex(pParse, pWC, pSrc, notReady, pOrderBy, pCost);
pCost->plan.wsFlags |= eqTermMask;
- WHERETRACE(("best index is %s, nrow=%.9g, cost=%.9g, wsFlags=%x, nEq=%d\n",
- (pCost->plan.wsFlags & WHERE_INDEXED)!=0 ?
- pCost->plan.u.pIdx->zName : "(none)", pCost->nRow,
- pCost->rCost, pCost->plan.wsFlags, pCost->plan.nEq));
}
/*
WhereCost bestPlan; /* Most efficient plan seen so far */
Index *pIdx; /* Index for FROM table at pTabItem */
int j; /* For looping over FROM tables */
- int bestJ = 0; /* The value of j */
+ int bestJ = -1; /* The value of j */
Bitmask m; /* Bitmask value for j or bestJ */
- int once = 0; /* True when first table is seen */
+ int isOptimal; /* Iterator for optimal/non-optimal search */
memset(&bestPlan, 0, sizeof(bestPlan));
bestPlan.rCost = SQLITE_BIG_DBL;
- for(j=iFrom, pTabItem=&pTabList->a[j]; j<pTabList->nSrc; j++, pTabItem++){
- int doNotReorder; /* True if this table should not be reordered */
- WhereCost sCost; /* Cost information from best[Virtual]Index() */
- ExprList *pOrderBy; /* ORDER BY clause for index to optimize */
-
- doNotReorder = (pTabItem->jointype & (JT_LEFT|JT_CROSS))!=0;
- if( once && doNotReorder ) break;
- m = getMask(pMaskSet, pTabItem->iCursor);
- if( (m & notReady)==0 ){
- if( j==iFrom ) iFrom++;
- continue;
- }
- pOrderBy = ((i==0 && ppOrderBy )?*ppOrderBy:0);
- assert( pTabItem->pTab );
+ /* Loop through the remaining entries in the FROM clause to find the
+ ** next nested loop. The FROM clause entries may be iterated through
+ ** either once or twice.
+ **
+ ** The first iteration, which is always performed, searches for the
+ ** FROM clause entry that permits the lowest-cost, "optimal" scan. In
+ ** this context an optimal scan is one that uses the same strategy
+ ** for the given FROM clause entry as would be selected if the entry
+ ** were used as the innermost nested loop.
+ **
+ ** The second iteration is only performed if no optimal scan strategies
+ ** were found by the first. This iteration is used to search for the
+ ** lowest cost scan overall.
+ **
+ ** Previous versions of SQLite performed only the second iteration -
+ ** the next outermost loop was always that with the lowest overall
+ ** cost. However, this meant that SQLite could select the wrong plan
+ ** for scripts such as the following:
+ **
+ ** CREATE TABLE t1(a, b);
+ ** CREATE TABLE t2(c, d);
+ ** SELECT * FROM t2, t1 WHERE t2.rowid = t1.a;
+ **
+ ** The best strategy is to iterate through table t1 first. However it
+ ** is not possible to determine this with a simple greedy algorithm.
+ ** However, since the cost of a linear scan through table t2 is the same
+ ** as the cost of a linear scan through table t1, a simple greedy
+ ** algorithm may choose to use t2 for the outer loop, which is a much
+ ** costlier approach.
+ */
+ for(isOptimal=1; isOptimal>=0 && bestJ<0; isOptimal--){
+ Bitmask mask = (isOptimal ? 0 : notReady);
+ assert( (pTabList->nSrc-iFrom)>1 || isOptimal );
+ for(j=iFrom, pTabItem=&pTabList->a[j]; j<pTabList->nSrc; j++, pTabItem++){
+ int doNotReorder; /* True if this table should not be reordered */
+ WhereCost sCost; /* Cost information from best[Virtual]Index() */
+ ExprList *pOrderBy; /* ORDER BY clause for index to optimize */
+
+ doNotReorder = (pTabItem->jointype & (JT_LEFT|JT_CROSS))!=0;
+ if( j!=iFrom && doNotReorder ) break;
+ m = getMask(pMaskSet, pTabItem->iCursor);
+ if( (m & notReady)==0 ){
+ if( j==iFrom ) iFrom++;
+ continue;
+ }
+ pOrderBy = ((i==0 && ppOrderBy )?*ppOrderBy:0);
+
+ assert( pTabItem->pTab );
#ifndef SQLITE_OMIT_VIRTUALTABLE
- if( IsVirtual(pTabItem->pTab) ){
- sqlite3_index_info **pp = &pWInfo->a[j].pIdxInfo;
- bestVirtualIndex(pParse, pWC, pTabItem, notReady, pOrderBy, &sCost, pp);
- }else
+ if( IsVirtual(pTabItem->pTab) ){
+ sqlite3_index_info **pp = &pWInfo->a[j].pIdxInfo;
+ bestVirtualIndex(pParse, pWC, pTabItem, mask, pOrderBy, &sCost, pp);
+ }else
#endif
- {
- bestBtreeIndex(pParse, pWC, pTabItem, notReady, pOrderBy, &sCost);
- }
- if( once==0 || sCost.rCost<bestPlan.rCost ){
- once = 1;
- bestPlan = sCost;
- bestJ = j;
+ {
+ bestBtreeIndex(pParse, pWC, pTabItem, mask, pOrderBy, &sCost);
+ }
+ assert( isOptimal || (sCost.used¬Ready)==0 );
+
+ if( (sCost.used¬Ready)==0
+ && (j==iFrom || sCost.rCost<bestPlan.rCost)
+ ){
+ bestPlan = sCost;
+ bestJ = j;
+ }
+ if( doNotReorder ) break;
}
- if( doNotReorder ) break;
}
- assert( once );
+ assert( bestJ>=0 );
assert( notReady & getMask(pMaskSet, pTabList->a[bestJ].iCursor) );
WHERETRACE(("*** Optimizer selects table %d for loop %d\n", bestJ,
pLevel-pWInfo->a));
projects / thirdparty / sqlite.git / commitdiff
