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Enhance whereLoopCheaperProperSubset(X,Y) so that it does not report true

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if X uses skip-scan less than Y, since in that case X might
deserve to be cheaper even if it is a proper subset.

FossilOrigin-Name: c106b755369c1f8546e897ecd2ac56fd09d6e885
This commit is contained in:
drh 2014-11-05 13:13:13 +00:00
parent 8d1edb92c4
commit e0de876e27
3 changed files with 15 additions and 13 deletions
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14
manifest
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@ -1,5 +1,5 @@
C Add\sthe\s".scanstats\son"\scommand\sto\sthe\sshell\stool.\sExecuting\sthis\scommand\scauses\sthe\sshell\stool\sto\sprint\svalues\sfrom\ssqlite3_stmt_scanstatus()\safter\seach\squery\sis\srun.
D 2014-11-05T09:07:28.365
C Enhance\swhereLoopCheaperProperSubset(X,Y)\sso\sthat\sit\sdoes\snot\sreport\strue\nif\sX\suses\sskip-scan\sless\sthan\sY,\ssince\sin\sthat\scase\sX\smight\ndeserve\sto\sbe\scheaper\seven\sif\sit\sis\sa\sproper\ssubset.
D 2014-11-05T13:13:13.983
F Makefile.arm-wince-mingw32ce-gcc d6df77f1f48d690bd73162294bbba7f59507c72f
F Makefile.in cf57f673d77606ab0f2d9627ca52a9ba1464146a
F Makefile.linux-gcc 91d710bdc4998cb015f39edf3cb314ec4f4d7e23
@ -302,7 +302,7 @@ F src/vtab.c 2a30791bbd7926b589401bd09c3abb33de563793
F src/wal.c 825c948066c7604a07d56e67958cdab210749016
F src/wal.h df01efe09c5cb8c8e391ff1715cca294f89668a4
F src/walker.c c253b95b4ee44b21c406e2a1052636c31ea27804
F src/where.c d5fa1081bf7cb70478ed06489e063695c92ee1e1
F src/where.c 240961041f35862ebcafd260587c79a1ab7347f8
F src/whereInt.h d3633e9b592103241b74b0ec76185f3e5b8b62e0
F test/8_3_names.test ebbb5cd36741350040fd28b432ceadf495be25b2
F test/aggerror.test a867e273ef9e3d7919f03ef4f0e8c0d2767944f2
@ -1211,7 +1211,7 @@ F tool/vdbe_profile.tcl 67746953071a9f8f2f668b73fe899074e2c6d8c1
F tool/warnings-clang.sh f6aa929dc20ef1f856af04a730772f59283631d4
F tool/warnings.sh 0abfd78ceb09b7f7c27c688c8e3fe93268a13b32
F tool/win/sqlite.vsix deb315d026cc8400325c5863eef847784a219a2f
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7974c0ed10ffdc960a43fed89845c2bed428958d
c106b755369c1f8546e897ecd2ac56fd09d6e885

12
src/where.c
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@ -4012,10 +4012,11 @@ static void whereInfoFree(sqlite3 *db, WhereInfo *pWInfo){
}
/*
** Return TRUE if both of the following are true:
** Return TRUE if all of the following are true:
**
** (1) X has the same or lower cost that Y
** (2) X is a proper subset of Y
** (3) X skips at least as many columns as Y
**
** By "proper subset" we mean that X uses fewer WHERE clause terms
** than Y and that every WHERE clause term used by X is also used
@ -4023,7 +4024,9 @@ static void whereInfoFree(sqlite3 *db, WhereInfo *pWInfo){
**
** If X is a proper subset of Y then Y is a better choice and ought
** to have a lower cost. This routine returns TRUE when that cost
** relationship is inverted and needs to be adjusted.
** relationship is inverted and needs to be adjusted. The third rule
** was added because if X uses skip-scan less than Y it still might
** deserve a lower cost even if it is a proper subset of Y.
*/
static int whereLoopCheaperProperSubset(
const WhereLoop *pX, /* First WhereLoop to compare */
@ -4033,6 +4036,7 @@ static int whereLoopCheaperProperSubset(
if( pX->nLTerm-pX->nSkip >= pY->nLTerm-pY->nSkip ){
return 0; /* X is not a subset of Y */
}
if( pY->nSkip > pX->nSkip ) return 0;
if( pX->rRun >= pY->rRun ){
if( pX->rRun > pY->rRun ) return 0; /* X costs more than Y */
if( pX->nOut > pY->nOut ) return 0; /* X costs more than Y */
@ -4068,9 +4072,7 @@ static void whereLoopAdjustCost(const WhereLoop *p, WhereLoop *pTemplate){
if( (p->wsFlags & WHERE_INDEXED)==0 ) continue;
if( whereLoopCheaperProperSubset(p, pTemplate) ){
/* Adjust pTemplate cost downward so that it is cheaper than its
** subset p. Except, do not adjust the cost estimate downward for
** a loop that skips more columns. */
if( pTemplate->nSkip>p->nSkip ) continue;
** subset p. */
WHERETRACE(0x80,("subset cost adjustment %d,%d to %d,%d\n",
pTemplate->rRun, pTemplate->nOut, p->rRun, p->nOut-1));
pTemplate->rRun = p->rRun;