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If a skip-scan is a proper subset of some other scan, then adjust the

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cost of the skip-scan upward so that it is more costly than the other scan.
Such a cost imbalance can arise under STAT4 because of difficulties in getting
an accurate estimate for skip-scans.

FossilOrigin-Name: f4b22a2620a5dc48949048c2ecbd226755d4b2c3
This commit is contained in:
drh
2014-10-21 01:05:09 +00:00
parent 40253262e0
commit c8bbce1e6a
5 changed files with 212 additions and 75 deletions
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4
src/whereInt.h
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@@ -115,7 +115,6 @@ struct WhereLoop {
union {
struct { /* Information for internal btree tables */
u16 nEq; /* Number of equality constraints */
u16 nSkip; /* Number of initial index columns to skip */
Index *pIndex; /* Index used, or NULL */
} btree;
struct { /* Information for virtual tables */
@@ -128,12 +127,13 @@ struct WhereLoop {
} u;
u32 wsFlags; /* WHERE_* flags describing the plan */
u16 nLTerm; /* Number of entries in aLTerm[] */
u16 nSkip; /* Number of NULL aLTerm[] entries */
/**** whereLoopXfer() copies fields above ***********************/
# define WHERE_LOOP_XFER_SZ offsetof(WhereLoop,nLSlot)
u16 nLSlot; /* Number of slots allocated for aLTerm[] */
WhereTerm **aLTerm; /* WhereTerms used */
WhereLoop *pNextLoop; /* Next WhereLoop object in the WhereClause */
WhereTerm *aLTermSpace[4]; /* Initial aLTerm[] space */
WhereTerm *aLTermSpace[3]; /* Initial aLTerm[] space */
};
/* This object holds the prerequisites and the cost of running a