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Overview
| Comment: | Change the cost estimator in the query planner to take into account the logN rowid lookup cost when going from an index to a table. |
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| Downloads: | Tarball | ZIP archive | SQL archive |
| Timelines: | family | ancestors | descendants | both | stat2-enhancement |
| Files: | files | file ages | folders |
| SHA1: | b442525b0ba642bb8d57b87b7b9e373b6046454a |
| User & Date: | drh 2011-01-24 15:11:23 |
Context
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2011-01-24
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| 17:46 | Restructuring and generalizing analyze5.test. The whole script is currently disabled and will need to be reenabled prior to merging with trunk. check-in: 31fcc706 user: drh tags: stat2-enhancement | |
| 15:11 | Change the cost estimator in the query planner to take into account the logN rowid lookup cost when going from an index to a table. check-in: b442525b user: drh tags: stat2-enhancement | |
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2011-01-22
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| 00:10 | Add the ability to use indices for constraints of the form "x IS NOT NULL" when sqlite_stat2 is available and most entries for column x are NULL. check-in: 5d5bddd2 user: drh tags: stat2-enhancement | |
Changes
Changes to src/where.c.
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whereEqualScanEst(pParse, pProbe, pFirstTerm->pExpr->pRight, &nRow);
}else if( pFirstTerm->eOperator==WO_IN && bInEst==0 ){
whereInScanEst(pParse, pProbe, pFirstTerm->pExpr->x.pList, &nRow);
}
}
#endif /* SQLITE_ENABLE_STAT2 */
/* Assume constant cost to access a row and logarithmic cost to
** do a binary search. Hence, the initial cost is the number of output
** rows plus log2(table-size) times the number of binary searches.
*/
cost = nRow + nInMul*estLog(aiRowEst[0]);
/* Adjust the number of rows and the cost downward to reflect rows
** that are excluded by range constraints.
*/
nRow = (nRow * (double)estBound) / (double)100;
cost = (cost * (double)estBound) / (double)100;
/* Add in the estimated cost of sorting the result
*/
if( bSort ){
cost += cost*estLog(cost);
}
/* If all information can be taken directly from the index, we avoid
** doing table lookups. This reduces the cost by half. (Not really -
** this needs to be fixed.)
*/
if( pIdx && bLookup==0 ){
cost /= (double)2;
}
/**** Cost of using this index has now been computed ****/
/* If there are additional constraints on this table that cannot
** be used with the current index, but which might lower the number
** of output rows, adjust the nRow value accordingly. This only
** matters if the current index is the least costly, so do not bother
** with this step if we already know this index will not be chosen.
|
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whereEqualScanEst(pParse, pProbe, pFirstTerm->pExpr->pRight, &nRow);
}else if( pFirstTerm->eOperator==WO_IN && bInEst==0 ){
whereInScanEst(pParse, pProbe, pFirstTerm->pExpr->x.pList, &nRow);
}
}
#endif /* SQLITE_ENABLE_STAT2 */
/* Adjust the number of rows and the cost downward to reflect rows
** that are excluded by range constraints.
*/
nRow = (nRow * (double)estBound) / (double)100;
/* Assume constant cost to access a row and logarithmic cost to
** do a binary search. Hence, the initial cost is the number of output
** rows plus log2(table-size) times the number of binary searches.
*/
if( pIdx && bLookup ){
cost = nRow + (nInMul+nRow)*estLog(aiRowEst[0]);
}else{
cost = nRow + nInMul*estLog(aiRowEst[0]);
}
/* Add in the estimated cost of sorting the result. This cost is expanded
** by a fudge factor of 3.0 to account for the fact that a sorting step
** involves a write and is thus more expensive than a lookup step.
*/
if( bSort ){
cost += nRow*estLog(nRow)*(double)3;
}
/**** Cost of using this index has now been computed ****/
/* If there are additional constraints on this table that cannot
** be used with the current index, but which might lower the number
** of output rows, adjust the nRow value accordingly. This only
** matters if the current index is the least costly, so do not bother
** with this step if we already know this index will not be chosen.
|