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Change the query planner to do a better job of estimating the number rows

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selected by a BETWEEN operator using STAT4 when both upper and lower bounds
are contained within the same sample.

FossilOrigin-Name: 2d36be5d9a1cdd4fd2d54fc4eeece32a81cbacc1
This commit is contained in:
drh
2014-11-05 19:26:12 +00:00
parent 6b5631e02f
commit 6d3f91d040
4 changed files with 33 additions and 25 deletions
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34
src/where.c
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@@ -1897,7 +1897,6 @@ static int vtabBestIndex(Parse *pParse, Table *pTab, sqlite3_index_info *p){
}
#endif /* !defined(SQLITE_OMIT_VIRTUALTABLE) */
#ifdef SQLITE_ENABLE_STAT3_OR_STAT4
/*
** Estimate the location of a particular key among all keys in an
@@ -1906,9 +1905,10 @@ static int vtabBestIndex(Parse *pParse, Table *pTab, sqlite3_index_info *p){
** aStat[0] Est. number of rows less than pVal
** aStat[1] Est. number of rows equal to pVal
**
** Return SQLITE_OK on success.
** Return the index of the sample that is the smallest sample that
** is greater than or equal to pRec.
*/
static void whereKeyStats(
static int whereKeyStats(
Parse *pParse, /* Database connection */
Index *pIdx, /* Index to consider domain of */
UnpackedRecord *pRec, /* Vector of values to consider */
@@ -1990,6 +1990,7 @@ static void whereKeyStats(
}
aStat[0] = iLower + iGap;
}
return i;
}
#endif /* SQLITE_ENABLE_STAT3_OR_STAT4 */
@@ -2140,7 +2141,7 @@ static int whereRangeSkipScanEst(
** If either of the upper or lower bound is not present, then NULL is passed in
** place of the corresponding WhereTerm.
**
** The value in (pBuilder->pNew->u.btree.nEq) is the index of the index
** The value in (pBuilder->pNew->u.btree.nEq) is the number of the index
** column subject to the range constraint. Or, equivalently, the number of
** equality constraints optimized by the proposed index scan. For example,
** assuming index p is on t1(a, b), and the SQL query is:
@@ -2156,7 +2157,7 @@ static int whereRangeSkipScanEst(
**
** When this function is called, *pnOut is set to the sqlite3LogEst() of the
** number of rows that the index scan is expected to visit without
** considering the range constraints. If nEq is 0, this is the number of
** considering the range constraints. If nEq is 0, then *pnOut is the number of
** rows in the index. Assuming no error occurs, *pnOut is adjusted (reduced)
** to account for the range constraints pLower and pUpper.
**
@@ -2180,9 +2181,7 @@ static int whereRangeScanEst(
Index *p = pLoop->u.btree.pIndex;
int nEq = pLoop->u.btree.nEq;
if( p->nSample>0
&& nEq<p->nSampleCol
){
if( p->nSample>0 && nEq<p->nSampleCol ){
if( nEq==pBuilder->nRecValid ){
UnpackedRecord *pRec = pBuilder->pRec;
tRowcnt a[2];
@@ -2198,15 +2197,19 @@ static int whereRangeScanEst(
** is not a simple variable or literal value), the lower bound of the
** range is $P. Due to a quirk in the way whereKeyStats() works, even
** if $L is available, whereKeyStats() is called for both ($P) and
** ($P:$L) and the larger of the two returned values used.
** ($P:$L) and the larger of the two returned values is used.
**
** Similarly, iUpper is to be set to the estimate of the number of rows
** less than the upper bound of the range query. Where the upper bound
** is either ($P) or ($P:$U). Again, even if $U is available, both values
** of iUpper are requested of whereKeyStats() and the smaller used.
**
** The number of rows between the two bounds is then just iUpper-iLower.
*/
tRowcnt iLower;
tRowcnt iUpper;
tRowcnt iLower; /* Rows less than the lower bound */
tRowcnt iUpper; /* Rows less than the upper bound */
int iLwrIdx = -2; /* aSample[] for the lower bound */
int iUprIdx = -1; /* aSample[] for the upper bound */
if( pRec ){
testcase( pRec->nField!=pBuilder->nRecValid );
@@ -2244,7 +2247,7 @@ static int whereRangeScanEst(
rc = sqlite3Stat4ProbeSetValue(pParse, p, &pRec, pExpr, aff, nEq, &bOk);
if( rc==SQLITE_OK && bOk ){
tRowcnt iNew;
whereKeyStats(pParse, p, pRec, 0, a);
iLwrIdx = whereKeyStats(pParse, p, pRec, 0, a);
iNew = a[0] + ((pLower->eOperator & (WO_GT|WO_LE)) ? a[1] : 0);
if( iNew>iLower ) iLower = iNew;
nOut--;
@@ -2259,7 +2262,7 @@ static int whereRangeScanEst(
rc = sqlite3Stat4ProbeSetValue(pParse, p, &pRec, pExpr, aff, nEq, &bOk);
if( rc==SQLITE_OK && bOk ){
tRowcnt iNew;
whereKeyStats(pParse, p, pRec, 1, a);
iUprIdx = whereKeyStats(pParse, p, pRec, 1, a);
iNew = a[0] + ((pUpper->eOperator & (WO_GT|WO_LE)) ? a[1] : 0);
if( iNew<iUpper ) iUpper = iNew;
nOut--;
@@ -2271,6 +2274,11 @@ static int whereRangeScanEst(
if( rc==SQLITE_OK ){
if( iUpper>iLower ){
nNew = sqlite3LogEst(iUpper - iLower);
/* TUNING: If both iUpper and iLower are derived from the same
** sample, then assume they are 4x more selective. This brings
** the estimated selectivity more in line with what it would be
** if estimated without the use of STAT3/4 tables. */
if( iLwrIdx==iUprIdx ) nNew -= 20; assert( 20==sqlite3LogEst(4) );
}else{
nNew = 10; assert( 10==sqlite3LogEst(2) );
}