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Simplify and add invariants to the WhereLoop merging logic inside of

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whereLoopInsert().

FossilOrigin-Name: 8f27f35f288434b9e7bc503c608f1e2b590ade4d
This commit is contained in:
drh
2013-06-19 12:34:13 +00:00
parent c7f0d229a7
commit dbb80234da
3 changed files with 26 additions and 26 deletions
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38
src/where.c
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@@ -4115,14 +4115,30 @@ static int whereLoopInsert(WhereLoopBuilder *pBuilder, WhereLoop *pTemplate){
** priority over pTemplate.
*/
for(ppPrev=&pWInfo->pLoops, p=*ppPrev; p; ppPrev=&p->pNextLoop, p=*ppPrev){
if( p->iTab!=pTemplate->iTab || p->iSortIdx!=pTemplate->iSortIdx ) continue;
if( p->iTab!=pTemplate->iTab || p->iSortIdx!=pTemplate->iSortIdx ){
/* If either the iTab or iSortIdx values for two WhereLoop are different
** then those WhereLoops need to be considered separately. Neither is
** a candidate to replace the other. */
continue;
}
/* In the current implementation, the rSetup value is either zero
** or the cost of building an automatic index (NlogN) and the NlogN
** is the same for compatible WhereLoops. */
assert( p->rSetup==0 || pTemplate->rSetup==0
|| p->rSetup==pTemplate->rSetup );
/* whereLoopAddBtree() always generates and inserts the automatic index
** case first. Hence compatible candidate WhereLoops never have a larger
** rSetup. Call this SETUP-INVARIANT */
assert( p->rSetup>=pTemplate->rSetup );
if( (p->prereq & pTemplate->prereq)==p->prereq
&& p->rSetup<=pTemplate->rSetup
&& p->rRun<=pTemplate->rRun
){
/* This branch taken when p is equal or better than pTemplate in
** all of (1) dependences (2) setup-cost, and (3) run-cost. */
testcase( p->rRun==pTemplate->rRun );
assert( p->rSetup==pTemplate->rSetup );
if( p->nLTerm<pTemplate->nLTerm
&& (p->wsFlags & WHERE_INDEXED)!=0
&& (pTemplate->wsFlags & WHERE_INDEXED)!=0
@@ -4133,38 +4149,22 @@ static int whereLoopInsert(WhereLoopBuilder *pBuilder, WhereLoop *pTemplate){
** more terms of the index */
pNext = p->pNextLoop;
break;
}else if( p->nOut>pTemplate->nOut
&& p->rSetup==pTemplate->rSetup
&& p->rRun==pTemplate->rRun
){
/* Overwrite an existing WhereLoop with the same cost but more
** outputs */
pNext = p->pNextLoop;
break;
}else{
/* pTemplate is not helpful.
** Return without changing or adding anything */
goto whereLoopInsert_noop;
}
}
testcase( (p->prereq & pTemplate->prereq)==p->prereq
&& p->rSetup<=pTemplate->rSetup
&& p->rRun==pTemplate->rRun+1 );
if( (p->prereq & pTemplate->prereq)==pTemplate->prereq
&& p->rSetup>=pTemplate->rSetup
&& p->rRun>=pTemplate->rRun
&& ALWAYS(p->rSetup>=pTemplate->rSetup) /* See SETUP-INVARIANT above */
){
/* Overwrite an existing WhereLoop with a better one: one that is
** better at one of (1) dependences, (2) setup-cost, or (3) run-cost
** and is no worse in any of those categories. */
testcase( p->rSetup==pTemplate->rSetup );
testcase( p->rRun==pTemplate->rRun );
pNext = p->pNextLoop;
break;
}
testcase( (p->prereq & pTemplate->prereq)==pTemplate->prereq
&& p->rSetup>=pTemplate->rSetup
&& p->rRun==pTemplate->rRun-1 );
}
/* If we reach this point it means that either p[] should be overwritten