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Overview
| Comment: | Increase the estimated cost of sorting when sorting wide results sets, to account for the extra storage space and I/O required for the external sort. |
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| Downloads: | Tarball | ZIP archive | SQL archive |
| Timelines: | family | ancestors | descendants | both | increased-sorting-cost |
| Files: | files | file ages | folders |
| SHA1: | aa0703e5cef0c61bec965d4c88ee48bb |
| User & Date: | drh 2017-02-16 21:29:53 |
Context
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2017-02-17
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| 21:23 | Increase the estimated cost of sorting when sorting wide results sets, to account for the extra storage space and I/O required for the external sort. Leaf check-in: 38298ef9 user: drh tags: apple-increased-sorting-cost | |
| 02:07 | Merge fixes from trunk. Leaf check-in: 662e8ccf user: drh tags: increased-sorting-cost | |
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2017-02-16
| ||
| 21:29 | Increase the estimated cost of sorting when sorting wide results sets, to account for the extra storage space and I/O required for the external sort. check-in: aa0703e5 user: drh tags: increased-sorting-cost | |
| 20:52 | Change the name of WhereInfo.pDistinctSet to pResultSet, since it is now used for more than just DISTINCT processing. check-in: 9fc5cd50 user: drh tags: trunk | |
Changes
Changes to src/where.c.
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**
** The (Y/X) term is implemented using stack variable rScale
** below. */
LogEst rScale, rSortCost;
assert( nOrderBy>0 && 66==sqlite3LogEst(100) );
rScale = sqlite3LogEst((nOrderBy-nSorted)*100/nOrderBy) - 66;
rSortCost = nRow + rScale + 16;
/* Multiple by log(M) where M is the number of output rows.
** Use the LIMIT for M if it is smaller */
if( (pWInfo->wctrlFlags & WHERE_USE_LIMIT)!=0 && pWInfo->iLimit<nRow ){
nRow = pWInfo->iLimit;
}
rSortCost += estLog(nRow);
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> > > > > > > > > > |
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** ** The (Y/X) term is implemented using stack variable rScale ** below. */ LogEst rScale, rSortCost; assert( nOrderBy>0 && 66==sqlite3LogEst(100) ); rScale = sqlite3LogEst((nOrderBy-nSorted)*100/nOrderBy) - 66; rSortCost = nRow + rScale + 16; /* For wide sorts (many payload columns) increase the sorting cost ** to account for the additional I/O used by the external sorting ** algorithm when it flushes PMAs to disk. */ if( pWInfo->pResultSet && pWInfo->pResultSet->nExpr>6 ){ rSortCost += sqlite3LogEst(pWInfo->pResultSet->nExpr) - 26; } /* Multiple by log(M) where M is the number of output rows. ** Use the LIMIT for M if it is smaller */ if( (pWInfo->wctrlFlags & WHERE_USE_LIMIT)!=0 && pWInfo->iLimit<nRow ){ nRow = pWInfo->iLimit; } rSortCost += estLog(nRow); |