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Improved comments an presentation for the recent IN operator decision

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improvement.

FossilOrigin-Name: 31e480f68dfd887cfd9114f9f9fec53d751d3ecc27e36f55c0166b51b2fbb08c
This commit is contained in:
drh
2018-06-09 14:13:46 +00:00
parent ccf6db5e64
commit a46ba6cca5
3 changed files with 10 additions and 9 deletions
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5
src/where.c
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@@ -2451,7 +2451,6 @@ static int whereLoopAddBtreeIndex(
if( eOp & WO_IN ){
Expr *pExpr = pTerm->pExpr;
LogEst M, logK;
if( ExprHasProperty(pExpr, EP_xIsSelect) ){
/* "x IN (SELECT ...)": TUNING: the SELECT returns 25 rows */
int i;
@@ -2472,6 +2471,7 @@ static int whereLoopAddBtreeIndex(
** changes "x IN (?)" into "x=?". */
}
if( pProbe->hasStat1 ){
LogEst M, logK, safetyMargin;
/* Let:
** N = the total number of rows in the table
** K = the number of entries on the RHS of the IN operator
@@ -2493,7 +2493,8 @@ static int whereLoopAddBtreeIndex(
*/
M = pProbe->aiRowLogEst[saved_nEq];
logK = estLog(nIn);
if( M + logK + 10 < nIn + rLogSize ){
safetyMargin = 10; /* TUNING: extra weight for indexed IN */
if( M + logK + safetyMargin < nIn + rLogSize ){
WHERETRACE(0x40,
("Scan preferred over IN operator on column %d of \"%s\" (%d<%d)\n",
saved_nEq, pProbe->zName, M+logK+10, nIn+rLogSize));