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Overview
| Comment: | The restriction on using automatic indexes for low cardinality loops only applies if the cardinality is restricted by a LIMIT clause. |
|---|---|
| Downloads: | Tarball | ZIP archive | SQL archive |
| Timelines: | family | ancestors | exp-indexed-clause |
| Files: | files | file ages | folders |
| SHA3-256: |
991a76bf427ade0059a3308454ebf1e7 |
| User & Date: | drh 2018-05-14 18:09:20 |
Context
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2018-05-14
| ||
| 18:09 | The restriction on using automatic indexes for low cardinality loops only applies if the cardinality is restricted by a LIMIT clause. Closed-Leaf check-in: 991a76bf user: drh tags: exp-indexed-clause | |
| 17:12 | Experimental syntax enhancement for an "INDEXED" keyword following a FROM-clause subquery that indicates that an automatic index on that subquery is suggested. check-in: 32b3d110 user: drh tags: exp-indexed-clause | |
Changes
Changes to src/where.c.
4001 4002 4003 4004 4005 4006 4007 4008 4009 4010 4011 4012 4013 4014 4015 4016 4017 |
LogEst rUnsorted; /* Unsorted cost of (pFrom+pWLoop) */
i8 isOrdered = pFrom->isOrdered; /* isOrdered for (pFrom+pWLoop) */
Bitmask maskNew; /* Mask of src visited by (..) */
Bitmask revMask = 0; /* Mask of rev-order loops for (..) */
if( (pWLoop->prereq & ~pFrom->maskLoop)!=0 ) continue;
if( (pWLoop->maskSelf & pFrom->maskLoop)!=0 ) continue;
if( (pWLoop->wsFlags & WHERE_AUTO_INDEX)!=0 && pFrom->nRow<10 ){
/* Do not use an automatic index if the this loop is expected
** to run less than 2 times. */
assert( 10==sqlite3LogEst(2) );
continue;
}
/* At this point, pWLoop is a candidate to be the next loop.
** Compute its cost */
rUnsorted = sqlite3LogEstAdd(pWLoop->rSetup,pWLoop->rRun + pFrom->nRow);
rUnsorted = sqlite3LogEstAdd(rUnsorted, pFrom->rUnsorted);
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| > > > | |
4001 4002 4003 4004 4005 4006 4007 4008 4009 4010 4011 4012 4013 4014 4015 4016 4017 4018 4019 4020 |
LogEst rUnsorted; /* Unsorted cost of (pFrom+pWLoop) */
i8 isOrdered = pFrom->isOrdered; /* isOrdered for (pFrom+pWLoop) */
Bitmask maskNew; /* Mask of src visited by (..) */
Bitmask revMask = 0; /* Mask of rev-order loops for (..) */
if( (pWLoop->prereq & ~pFrom->maskLoop)!=0 ) continue;
if( (pWLoop->maskSelf & pFrom->maskLoop)!=0 ) continue;
if( (pWLoop->wsFlags & WHERE_AUTO_INDEX)!=0
&& (pWInfo->wctrlFlags & WHERE_USE_LIMIT)!=0
&& pWInfo->iLimit<10
){
/* Do not use an automatic index if the this loop is expected
** to run less than twice due to a LIMIT clause. */
assert( 10==sqlite3LogEst(2) );
continue;
}
/* At this point, pWLoop is a candidate to be the next loop.
** Compute its cost */
rUnsorted = sqlite3LogEstAdd(pWLoop->rSetup,pWLoop->rRun + pFrom->nRow);
rUnsorted = sqlite3LogEstAdd(rUnsorted, pFrom->rUnsorted);
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