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Query planner heuristic update:

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When doing a full table scan on a table that has an equality constraint on
an unindexed column, do not allow the estimated number of output rows to
be greater than half the total number of rows in the table.

FossilOrigin-Name: 73954f93c4c6f880c6e01d0d130e3fed40fd4106
This commit is contained in:
drh
2014-09-06 01:35:57 +00:00
parent 30c633a097
commit d8b77e20fc
5 changed files with 297 additions and 61 deletions
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34
src/where.c
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@@ -4221,14 +4221,16 @@ static int whereLoopInsert(WhereLoopBuilder *pBuilder, WhereLoop *pTemplate){
** the number of output rows by a factor of 10 and each additional term
** reduces the number of output rows by sqrt(2).
*/
static void whereLoopOutputAdjust(WhereClause *pWC, WhereLoop *pLoop){
static void whereLoopOutputAdjust(
WhereClause *pWC, /* The WHERE clause */
WhereLoop *pLoop, /* The loop to adjust downward */
LogEst nRow /* Number of rows in the entire table */
){
WhereTerm *pTerm, *pX;
Bitmask notAllowed = ~(pLoop->prereq|pLoop->maskSelf);
int i, j;
int nEq = 0; /* Number of = constraints not within likely()/unlike() */
if( !OptimizationEnabled(pWC->pWInfo->pParse->db, SQLITE_AdjustOutEst) ){
return;
}
for(i=pWC->nTerm, pTerm=pWC->a; i>0; i--, pTerm++){
if( (pTerm->wtFlags & TERM_VIRTUAL)!=0 ) break;
if( (pTerm->prereqAll & pLoop->maskSelf)==0 ) continue;
@@ -4240,9 +4242,21 @@ static void whereLoopOutputAdjust(WhereClause *pWC, WhereLoop *pLoop){
if( pX->iParent>=0 && (&pWC->a[pX->iParent])==pTerm ) break;
}
if( j<0 ){
pLoop->nOut += (pTerm->truthProb<=0 ? pTerm->truthProb : -1);
if( pTerm->truthProb<=0 ){
pLoop->nOut += pTerm->truthProb;
}else{
pLoop->nOut--;
if( pTerm->eOperator&WO_EQ ) nEq++;
}
}
}
/* TUNING: If there is at least one equality constraint in the WHERE
** clause that does not have a likelihood() explicitly assigned to it
** then do not let the estimated number of output rows exceed half
** the number of rows in the table. */
if( nEq && pLoop->nOut>nRow-10 ){
pLoop->nOut = nRow - 10;
}
}
/*
@@ -4288,6 +4302,7 @@ static int whereLoopAddBtreeIndex(
LogEst saved_nOut; /* Original value of pNew->nOut */
int iCol; /* Index of the column in the table */
int rc = SQLITE_OK; /* Return code */
LogEst rSize; /* Number of rows in the table */
LogEst rLogSize; /* Logarithm of table size */
WhereTerm *pTop = 0, *pBtm = 0; /* Top and bottom range constraints */
@@ -4317,7 +4332,8 @@ static int whereLoopAddBtreeIndex(
saved_prereq = pNew->prereq;
saved_nOut = pNew->nOut;
pNew->rSetup = 0;
rLogSize = estLog(pProbe->aiRowLogEst[0]);
rSize = pProbe->aiRowLogEst[0];
rLogSize = estLog(rSize);
/* Consider using a skip-scan if there are no WHERE clause constraints
** available for the left-most terms of the index, and if the average
@@ -4494,7 +4510,7 @@ static int whereLoopAddBtreeIndex(
nOutUnadjusted = pNew->nOut;
pNew->rRun += nInMul + nIn;
pNew->nOut += nInMul + nIn;
whereLoopOutputAdjust(pBuilder->pWC, pNew);
whereLoopOutputAdjust(pBuilder->pWC, pNew, rSize);
rc = whereLoopInsert(pBuilder, pNew);
if( pNew->wsFlags & WHERE_COLUMN_RANGE ){
@@ -4748,7 +4764,7 @@ static int whereLoopAddBtree(
/* TUNING: Cost of full table scan is (N*3.0). */
pNew->rRun = rSize + 16;
ApplyCostMultiplier(pNew->rRun, pTab->costMult);
whereLoopOutputAdjust(pWC, pNew);
whereLoopOutputAdjust(pWC, pNew, rSize);
rc = whereLoopInsert(pBuilder, pNew);
pNew->nOut = rSize;
if( rc ) break;
@@ -4784,7 +4800,7 @@ static int whereLoopAddBtree(
pNew->rRun = sqlite3LogEstAdd(pNew->rRun, rSize+16);
}
ApplyCostMultiplier(pNew->rRun, pTab->costMult);
whereLoopOutputAdjust(pWC, pNew);
whereLoopOutputAdjust(pWC, pNew, rSize);
rc = whereLoopInsert(pBuilder, pNew);
pNew->nOut = rSize;
if( rc ) break;