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Fix the query planner so that when it has a choice of full-scan tables to

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move to the outer loop, it chooses the one that is likely to give the fewest
output rows.

FossilOrigin-Name: 309bbedf9648c750d7b8aedbc15d4fd68f846824
This commit is contained in:
drh
2010-08-05 02:52:32 +00:00
parent 5e377d90ed
commit aa0ba4345d
4 changed files with 65 additions and 22 deletions
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39
src/where.c
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@@ -4065,6 +4065,7 @@ WhereInfo *sqlite3WhereBegin(
Bitmask m; /* Bitmask value for j or bestJ */
int isOptimal; /* Iterator for optimal/non-optimal search */
int nUnconstrained; /* Number tables without INDEXED BY */
Bitmask notIndexed; /* Mask of tables that cannot use an index */
memset(&bestPlan, 0, sizeof(bestPlan));
bestPlan.rCost = SQLITE_BIG_DBL;
@@ -4107,8 +4108,9 @@ WhereInfo *sqlite3WhereBegin(
** costlier approach.
*/
nUnconstrained = 0;
notIndexed = 0;
for(isOptimal=(iFrom<nTabList-1); isOptimal>=0; isOptimal--){
Bitmask mask; /* Mask of tables not yet ready */
Bitmask mask; /* Mask of tables not yet ready */
for(j=iFrom, pTabItem=&pTabList->a[j]; j<nTabList; j++, pTabItem++){
int doNotReorder; /* True if this table should not be reordered */
WhereCost sCost; /* Cost information from best[Virtual]Index() */
@@ -4137,28 +4139,43 @@ WhereInfo *sqlite3WhereBegin(
}
assert( isOptimal || (sCost.used&notReady)==0 );
/* If an INDEXED BY clause is present, then the plan must use that
** index if it uses any index at all */
assert( pTabItem->pIndex==0
|| (sCost.plan.wsFlags & WHERE_NOT_FULLSCAN)==0
|| sCost.plan.u.pIdx==pTabItem->pIndex );
if( isOptimal && (sCost.plan.wsFlags & WHERE_NOT_FULLSCAN)==0 ){
notIndexed |= m;
}
/* Conditions under which this table becomes the best so far:
**
** (1) The table must not depend on other tables that have not
** yet run.
**
** (2) A full-table-scan plan cannot supercede another plan unless
** the full-table-scan is an optimal plan.
** it is an "optimal" plan as defined above.
**
** (3) The plan cost must be lower than prior plans or else the
** cost must be the same and the number of rows must be lower.
**
** (4) All tables have an INDEXED BY clause or this table lacks an
** (3) All tables have an INDEXED BY clause or this table lacks an
** INDEXED BY clause or this table uses the specific
** index specified by its INDEXED BY clause.
** index specified by its INDEXED BY clause. This rule ensures
** that a best-so-far is always selected even if an impossible
** combination of INDEXED BY clauses are given. The error
** will be detected and relayed back to the application later.
** The NEVER() comes about because rule (2) above prevents
** An indexable full-table-scan from reaching rule (3).
**
** (4) The plan cost must be lower than prior plans or else the
** cost must be the same and the number of rows must be lower.
*/
if( (sCost.used&notReady)==0 /* (1) */
&& (bestJ<0 || isOptimal /* (2) */
&& (bestJ<0 || (notIndexed&m)!=0 /* (2) */
|| (sCost.plan.wsFlags & WHERE_NOT_FULLSCAN)!=0)
&& (bestJ<0 || sCost.rCost<bestPlan.rCost /* (3) */
&& (nUnconstrained==0 || pTabItem->pIndex==0 /* (3) */
|| NEVER((sCost.plan.wsFlags & WHERE_NOT_FULLSCAN)!=0))
&& (bestJ<0 || sCost.rCost<bestPlan.rCost /* (4) */
|| (sCost.rCost<=bestPlan.rCost && sCost.nRow<bestPlan.nRow))
&& (nUnconstrained==0 || pTabItem->pIndex==0 /* (4) */
|| pTabItem->pIndex==sCost.plan.u.pIdx)
){
WHERETRACE(("... best so far with cost=%g and nRow=%g\n",
sCost.rCost, sCost.nRow));