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Overview
| Comment: | Use a binary search instead of a linear scan when comparing a sample key against data from the sqlite_stat4 table. |
|---|---|
| Downloads: | Tarball | ZIP archive | SQL archive |
| Timelines: | family | ancestors | descendants | both | sqlite_stat4 |
| Files: | files | file ages | folders |
| SHA1: |
e50dc30523210ba12324d5d837950361 |
| User & Date: | dan 2013-08-08 16:17:12 |
Context
|
2013-08-08
| ||
| 19:38 | Fix problems in estimating the number of rows visited by a range query using sqlite_stat4 data when the column subject to the range query is not the leftmost of the index. check-in: 9228aaf5 user: dan tags: sqlite_stat4 | |
| 16:17 | Use a binary search instead of a linear scan when comparing a sample key against data from the sqlite_stat4 table. check-in: e50dc305 user: dan tags: sqlite_stat4 | |
| 12:21 | Fix a segfault in "ALTER TABLE t1 ADD COLUMN b DEFAULT (-+1)". Also an assert() failure that could occur if SQLITE_ENABLE_STAT4 were not defined. check-in: 9fec3e38 user: dan tags: sqlite_stat4 | |
Changes
Changes to src/where.c.
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Parse *pParse, /* Database connection */
Index *pIdx, /* Index to consider domain of */
UnpackedRecord *pRec, /* Vector of values to consider */
int roundUp, /* Round up if true. Round down if false */
tRowcnt *aStat /* OUT: stats written here */
){
IndexSample *aSample = pIdx->aSample;
int i;
int isEq = 0;
int iCol = pRec->nField-1;
assert( pRec->nField>0 && iCol<pIdx->nColumn );
for(i=0; i<pIdx->nSample; i++){
int res = sqlite3VdbeRecordCompare(aSample[i].n, aSample[i].p, pRec);
if( res>=0 ){
isEq = (res==0);
break;
}
}
/* At this point, aSample[i] is the first sample that is greater than
** or equal to pVal. Or if i==pIdx->nSample, then all samples are less
** than pVal. If aSample[i]==pVal, then isEq==1.
*/
if( isEq ){
assert( i<pIdx->nSample );
aStat[0] = aSample[i].anLt[iCol];
aStat[1] = aSample[i].anEq[iCol];
}else{
tRowcnt iLower, iUpper, iGap;
if( i==0 ){
iLower = 0;
iUpper = aSample[0].anLt[iCol];
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Parse *pParse, /* Database connection */
Index *pIdx, /* Index to consider domain of */
UnpackedRecord *pRec, /* Vector of values to consider */
int roundUp, /* Round up if true. Round down if false */
tRowcnt *aStat /* OUT: stats written here */
){
IndexSample *aSample = pIdx->aSample;
int iCol = pRec->nField-1; /* Index of required stats in anEq[] etc. */
int iMin = 0; /* Smallest sample not yet tested */
int i = pIdx->nSample; /* Smallest sample larger than or equal to pRec */
int iTest; /* Next sample to test */
int res; /* Result of comparison operation */
assert( pIdx->nSample>0 );
assert( pRec->nField>0 && iCol<pIdx->nColumn );
do{
iTest = (iMin+i)/2;
res = sqlite3VdbeRecordCompare(aSample[iTest].n, aSample[iTest].p, pRec);
if( res<0 ){
iMin = iTest+1;
}else{
i = iTest;
}
}while( res && iMin<i );
#ifdef SQLITE_DEBUG
/* The following assert statements check that the binary search code
** above found the right answer. This block serves no purpose other
** than to invoke the asserts. */
if( res==0 ){
/* If (res==0) is true, then sample $i must be equal to pRec */
assert( i<pIdx->nSample );
assert( 0==sqlite3VdbeRecordCompare(aSample[i].n, aSample[i].p, pRec) );
}else{
/* Otherwise, pRec must be smaller than sample $i and larger than
** sample ($i-1). */
assert( i==pIdx->nSample
|| sqlite3VdbeRecordCompare(aSample[i].n, aSample[i].p, pRec)>0 );
assert( i==0
|| sqlite3VdbeRecordCompare(aSample[i-1].n, aSample[i-1].p, pRec)<0 );
}
#endif /* ifdef SQLITE_DEBUG */
/* At this point, aSample[i] is the first sample that is greater than
** or equal to pVal. Or if i==pIdx->nSample, then all samples are less
** than pVal. If aSample[i]==pVal, then res==0.
*/
if( res==0 ){
aStat[0] = aSample[i].anLt[iCol];
aStat[1] = aSample[i].anEq[iCol];
}else{
tRowcnt iLower, iUpper, iGap;
if( i==0 ){
iLower = 0;
iUpper = aSample[0].anLt[iCol];
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