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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 | apple-increased-sorting-cost |
| Files: | files | file ages | folders |
| SHA1: |
38298ef923c8dad6860385ac4a20849e |
| User & Date: | drh 2017-02-17 21:23:25 |
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) | |
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2017-02-16
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| 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) | |
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2016-11-17
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| 14:02 | When opening the *-shm file for a readonly database, try to open it in read-write mode before falling back to readonly. This is in case some other read/write connection within the same process uses the same file descriptor. (check-in: a07c581e user: dan tags: apple-osx) | |
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->pDistinctSet && pWInfo->pDistinctSet->nExpr>6 ){ rSortCost += sqlite3LogEst(pWInfo->pDistinctSet->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); |