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Improvements to cost estimation for evaluating the IN operator.

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Ticket #3757. (CVS 6403)

FossilOrigin-Name: 0c438e813c411e8f9e92d6c7405fccb7a36e110a
This commit is contained in:
drh
2009-03-29 00:13:03 +00:00
parent f48f9ca65c
commit 75572e9de9
4 changed files with 93 additions and 15 deletions
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33
src/where.c
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@@ -16,7 +16,7 @@
** so is applicable. Because this module is responsible for selecting
** indices, you might also think of this module as the "query optimizer".
**
** $Id: where.c,v 1.377 2009/03/25 16:51:43 drh Exp $
** $Id: where.c,v 1.378 2009/03/29 00:13:03 drh Exp $
*/
#include "sqliteInt.h"
@@ -26,7 +26,7 @@
#if defined(SQLITE_TEST) || defined(SQLITE_DEBUG)
int sqlite3WhereTrace = 0;
#endif
#if 0
#if 1
# define WHERETRACE(X) if(sqlite3WhereTrace) sqlite3DebugPrintf X
#else
# define WHERETRACE(X)
@@ -1926,12 +1926,18 @@ static void bestIndex(
pProbe = pSrc->pIndex;
}
for(; pProbe; pProbe=(pSrc->pIndex ? 0 : pProbe->pNext)){
double inMultiplier = 1;
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 constraints or x IN (...) constraints.
** by x=EXPR constraints or x IN (...) constraints. For a term
** of the form x=EXPR 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.
*/
wsFlags = 0;
for(i=0; i<pProbe->nColumn; i++){
@@ -1944,21 +1950,31 @@ static void bestIndex(
wsFlags |= WHERE_COLUMN_IN;
if( ExprHasProperty(pExpr, EP_xIsSelect) ){
inMultiplier *= 25;
inMultIsEst = 1;
}else if( pExpr->x.pList ){
inMultiplier *= pExpr->x.pList->nExpr + 1;
}
}
}
nRow = pProbe->aiRowEst[i] * inMultiplier;
cost = nRow * estLog(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 && (wsFlags & WHERE_COLUMN_IN)==0
&& nEq==pProbe->nColumn ){
wsFlags |= WHERE_UNIQUE;
}
WHERETRACE(("...... nEq=%d inMult=%.9g cost=%.9g\n",nEq,inMultiplier,cost));
WHERETRACE(("...... nEq=%d inMult=%.9g nRow=%.9g cost=%.9g\n",
nEq, inMultiplier, nRow, cost));
/* Look for range constraints
/* Look for range constraints. Assume that each range constraint
** makes the search space 1/3rd smaller.
*/
if( nEq<pProbe->nColumn ){
int j = pProbe->aiColumn[nEq];
@@ -1975,7 +1991,8 @@ static void bestIndex(
cost /= 3;
nRow /= 3;
}
WHERETRACE(("...... range reduces cost to %.9g\n", cost));
WHERETRACE(("...... range reduces nRow to %.9g and cost to %.9g\n",
nRow, cost));
}
}