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Overview
| Comment: | Lower the threshold for using skip-scan from 50 to 18, based on experiments that show that 18 is the approximate break-even point for a variety of schemas. |
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| Downloads: | Tarball | ZIP archive | SQL archive |
| Timelines: | family | ancestors | descendants | both | trunk |
| Files: | files | file ages | folders |
| SHA1: |
83c0bb9913838d18ba355033afde6e38 |
| User & Date: | drh 2013-11-27 04:22:27 |
Context
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2013-11-27
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| 13:24 | Make sure the colWidth array is correctly initialized in the ".explain" command of the shell. check-in: ceebcdca user: drh tags: trunk | |
| 04:22 | Lower the threshold for using skip-scan from 50 to 18, based on experiments that show that 18 is the approximate break-even point for a variety of schemas. check-in: 83c0bb99 user: drh tags: trunk | |
| 04:00 | Avoid using the GetVersionEx functions if they are considered deprecated. check-in: afdca299 user: mistachkin tags: trunk | |
Changes
Changes to src/where.c.
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saved_prereq = pNew->prereq; saved_nOut = pNew->nOut; pNew->rSetup = 0; rLogSize = estLog(sqlite3LogEst(pProbe->aiRowEst[0])); /* 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 ** number of repeats in the left-most terms is at least 50. */ if( pTerm==0 && saved_nEq==saved_nSkip && saved_nEq+1<pProbe->nKeyCol && pProbe->aiRowEst[saved_nEq+1]>50 /* TUNING: Minimum for skip-scan */ ){ LogEst nIter; pNew->u.btree.nEq++; pNew->u.btree.nSkip++; pNew->aLTerm[pNew->nLTerm++] = 0; pNew->wsFlags |= WHERE_SKIPSCAN; nIter = sqlite3LogEst(pProbe->aiRowEst[0]/pProbe->aiRowEst[saved_nEq+1]); |
| > > | |
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saved_prereq = pNew->prereq; saved_nOut = pNew->nOut; pNew->rSetup = 0; rLogSize = estLog(sqlite3LogEst(pProbe->aiRowEst[0])); /* 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 ** number of repeats in the left-most terms is at least 18. The magic ** number 18 was found by experimentation to be the payoff point where ** skip-scan become faster than a full-scan. */ if( pTerm==0 && saved_nEq==saved_nSkip && saved_nEq+1<pProbe->nKeyCol && pProbe->aiRowEst[saved_nEq+1]>=18 /* TUNING: Minimum for skip-scan */ ){ LogEst nIter; pNew->u.btree.nEq++; pNew->u.btree.nSkip++; pNew->aLTerm[pNew->nLTerm++] = 0; pNew->wsFlags |= WHERE_SKIPSCAN; nIter = sqlite3LogEst(pProbe->aiRowEst[0]/pProbe->aiRowEst[saved_nEq+1]); |