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| author | drh <drh@noemail.net> | 2014-09-23 01:40:59 +0000 |
|---|---|---|
| committer | drh <drh@noemail.net> | 2014-09-23 01:40:59 +0000 |
| commit | 14f0e2128ac9cbbe5e1e871372911e3df447df4f (patch) | |
| tree | 3c7a787a8c6407a2a6f44b0b4ee918c2a3a341bc /src | |
| parent | a4bb5b0726772476cdf36b4a0182e27a73fab557 (diff) | |
| download | sqlite-14f0e2128ac9cbbe5e1e871372911e3df447df4f.tar.gz sqlite-14f0e2128ac9cbbe5e1e871372911e3df447df4f.zip | |
Adjust skip-scan cost estimates slightly so that a full table scan is
preferred over a skip-scan to a column with only two distinct values.
FossilOrigin-Name: ae9a42b268ad3f7d21a5813bb931e795c6917014
Diffstat (limited to 'src')
| -rw-r--r-- | src/where.c | 5 |
1 files changed, 4 insertions, 1 deletions
diff --git a/src/where.c b/src/where.c index d1862b499..40f95acc4 100644 --- a/src/where.c +++ b/src/where.c @@ -4359,11 +4359,14 @@ static int whereLoopAddBtreeIndex( nIter = pProbe->aiRowLogEst[saved_nEq] - pProbe->aiRowLogEst[saved_nEq+1]; if( pTerm ){ /* TUNING: When estimating skip-scan for a term that is also indexable, - ** increase the cost of the skip-scan by 2x, to make it a little less + ** multiply the cost of the skip-scan by 2.0, to make it a little less ** desirable than the regular index lookup. */ nIter += 10; assert( 10==sqlite3LogEst(2) ); } pNew->nOut -= nIter; + /* TUNING: Because uncertainties in the estimates for skip-scan queries, + ** add a 1.375 fudge factor to make skip-scan slightly less likely. */ + nIter += 5; whereLoopAddBtreeIndex(pBuilder, pSrc, pProbe, nIter + nInMul); pNew->nOut = saved_nOut; pNew->u.btree.nEq = saved_nEq; |