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Improvements to query planning for joins: Avoid unnecessary calls to

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"optimal scan" checks in cases where table reordering is not possible.
Make sure optimal scan checks are carried out for CROSS JOINs and LEFT
JOINs.

FossilOrigin-Name: d5ebb7877885839e93eee3b322624d4c4215c1c4
This commit is contained in:
drh 2013-01-16 00:46:09 +00:00
parent ea84a65e4e
commit 3bd5ab8638
3 changed files with 47 additions and 14 deletions
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12
manifest
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@ -1,5 +1,5 @@
C Fix\sa\smissing\sword\sin\sa\scomment.\s\sEnhance\sthe\s"wheretrace"\sdebugging\soutput\nto\sshow\sthe\sestimated\scost\sof\seach\stable\soption\swhile\splanning\sthe\sjoin\sorder.
D 2013-01-15T18:49:07.627
C Improvements\sto\squery\splanning\sfor\sjoins:\s\sAvoid\sunnecessary\scalls\sto\n"optimal\sscan"\schecks\sin\scases\swhere\stable\sreordering\sis\snot\spossible.\nMake\ssure\soptimal\sscan\schecks\sare\scarried\sout\sfor\sCROSS\sJOINs\sand\sLEFT\nJOINs.
D 2013-01-16T00:46:09.175
F Makefile.arm-wince-mingw32ce-gcc d6df77f1f48d690bd73162294bbba7f59507c72f
F Makefile.in a48faa9e7dd7d556d84f5456eabe5825dd8a6282
F Makefile.linux-gcc 91d710bdc4998cb015f39edf3cb314ec4f4d7e23
@ -252,7 +252,7 @@ F src/vtab.c b05e5f1f4902461ba9f5fc49bb7eb7c3a0741a83
F src/wal.c f5c7b5027d0ed0e9bc9afeb4a3a8dfea762ec7d2
F src/wal.h 29c197540b19044e6cd73487017e5e47a1d3dac6
F src/walker.c 3d75ba73de15e0f8cd0737643badbeb0e002f07b
F src/where.c b2a827f2b3fa23a3245a4e6093827e359c1e8054
F src/where.c d48a57d8afd97c51f1b772ebd72431a43a0e48b3
F test/8_3_names.test 631ea964a3edb091cf73c3b540f6bcfdb36ce823
F test/aggerror.test a867e273ef9e3d7919f03ef4f0e8c0d2767944f2
F test/aggnested.test 45c0201e28045ad38a530b5a144b73cd4aa2cfd6
@ -1033,7 +1033,7 @@ F tool/vdbe-compress.tcl f12c884766bd14277f4fcedcae07078011717381
F tool/warnings-clang.sh f6aa929dc20ef1f856af04a730772f59283631d4
F tool/warnings.sh fbc018d67fd7395f440c28f33ef0f94420226381
F tool/win/sqlite.vsix 97894c2790eda7b5bce3cc79cb2a8ec2fde9b3ac
P 04507c176330a06b09dcafa35ec0ca7498f5ace7
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P ac4e119a87497f2e422ff1cb711112ed8594bfa9
R 604db48c0336d28f8c2561951db4000b
U drh
Z f7bf9c2b2fa73cf7872c5f7a932db154
Z 14d78037173bf002814299854e4b798b

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ac4e119a87497f2e422ff1cb711112ed8594bfa9
d5ebb7877885839e93eee3b322624d4c4215c1c4

47
src/where.c
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@ -5072,6 +5072,7 @@ WhereInfo *sqlite3WhereBegin(
int bestJ = -1; /* The value of j */
Bitmask m; /* Bitmask value for j or bestJ */
int isOptimal; /* Iterator for optimal/non-optimal search */
int ckOptimal; /* Do the optimal scan check */
int nUnconstrained; /* Number tables without INDEXED BY */
Bitmask notIndexed; /* Mask of tables that cannot use an index */
@ -5122,17 +5123,41 @@ WhereInfo *sqlite3WhereBegin(
*/
nUnconstrained = 0;
notIndexed = 0;
for(isOptimal=(iFrom<nTabList-1); isOptimal>=0 && bestJ<0; isOptimal--){
/* The optimal scan check only occurs if there are two or more tables
** available to be reordered */
if( iFrom==nTabList-1 ){
ckOptimal = 0; /* Common case of just one table in the FROM clause */
}else{
ckOptimal = -1;
for(j=iFrom, sWBI.pSrc=&pTabList->a[j]; j<nTabList; j++, sWBI.pSrc++){
int doNotReorder; /* True if this table should not be reordered */
doNotReorder = (sWBI.pSrc->jointype & (JT_LEFT|JT_CROSS))!=0;
if( j!=iFrom && doNotReorder ) break;
m = getMask(pMaskSet, sWBI.pSrc->iCursor);
if( (m & sWBI.notValid)==0 ){
if( j==iFrom ) iFrom++;
continue;
}
if( j>iFrom && (sWBI.pSrc->jointype & (JT_LEFT|JT_CROSS))!=0 ) break;
if( ++ckOptimal ) break;
if( (sWBI.pSrc->jointype & JT_LEFT)!=0 ) break;
}
}
assert( ckOptimal==0 || ckOptimal==1 );
for(isOptimal=ckOptimal; isOptimal>=0 && bestJ<0; isOptimal--){
for(j=iFrom, sWBI.pSrc=&pTabList->a[j]; j<nTabList; j++, sWBI.pSrc++){
if( j>iFrom && (sWBI.pSrc->jointype & (JT_LEFT|JT_CROSS))!=0 ){
/* This break and one like it in the ckOptimal computation loop
** above prevent table reordering across LEFT and CROSS JOINs.
** The LEFT JOIN case is necessary for correctness. The prohibition
** against reordering across a CROSS JOIN is an SQLite feature that
** allows the developer to control table reordering */
break;
}
m = getMask(pMaskSet, sWBI.pSrc->iCursor);
if( (m & sWBI.notValid)==0 ){
assert( j>iFrom );
continue;
}
sWBI.notReady = (isOptimal ? m : sWBI.notValid);
if( sWBI.pSrc->pIndex==0 ) nUnconstrained++;
@ -5161,7 +5186,7 @@ WhereInfo *sqlite3WhereBegin(
}
if( isOptimal ){
pWInfo->a[j].rOptCost = sWBI.cost.rCost;
}else if( iFrom<nTabList-1 ){
}else if( ckOptimal ){
/* If two or more tables have nearly the same outer loop cost, but
** very different inner loop (optimal) cost, we want to choose
** for the outer loop that table which benefits the least from
@ -5207,11 +5232,19 @@ WhereInfo *sqlite3WhereBegin(
bestPlan = sWBI.cost;
bestJ = j;
}
if( doNotReorder ) break;
/* In a join like "w JOIN x LEFT JOIN y JOIN z" make sure that
** table y (and not table z) is always the next inner loop inside
** of table x. */
if( (sWBI.pSrc->jointype & JT_LEFT)!=0 ) break;
}
}
assert( bestJ>=0 );
assert( sWBI.notValid & getMask(pMaskSet, pTabList->a[bestJ].iCursor) );
assert( bestJ==iFrom || (pTabList->a[iFrom].jointype & JT_LEFT)==0 );
testcase( bestJ>iFrom && (pTabList->a[iFrom].jointype & JT_CROSS)!=0 );
testcase( bestJ>iFrom && bestJ<nTabList-1
&& (pTabList->a[bestJ+1].jointype & JT_LEFT)!=0 );
WHERETRACE(("*** Optimizer selects table %d (%s) for loop %d with:\n"
" cost=%.1f, nRow=%.1f, nOBSat=%d, wsFlags=0x%08x\n",
bestJ, pTabList->a[bestJ].pTab->zName,