diff options
Diffstat (limited to 'src/backend/optimizer/path/clausesel.c')
| -rw-r--r-- | src/backend/optimizer/path/clausesel.c | 75 |
1 files changed, 45 insertions, 30 deletions
diff --git a/src/backend/optimizer/path/clausesel.c b/src/backend/optimizer/path/clausesel.c index 5566b74b0c1..2e53294e232 100644 --- a/src/backend/optimizer/path/clausesel.c +++ b/src/backend/optimizer/path/clausesel.c @@ -8,7 +8,7 @@ * * * IDENTIFICATION - * $PostgreSQL: pgsql/src/backend/optimizer/path/clausesel.c,v 1.70 2004/08/29 05:06:43 momjian Exp $ + * $PostgreSQL: pgsql/src/backend/optimizer/path/clausesel.c,v 1.71 2004/11/09 00:34:38 tgl Exp $ * *------------------------------------------------------------------------- */ @@ -80,9 +80,10 @@ static void addRangeClause(RangeQueryClause **rqlist, Node *clause, * interpreting it as a value. Then the available range is 1-losel to hisel. * However, this calculation double-excludes nulls, so really we need * hisel + losel + null_frac - 1.) - * If the calculation yields zero or negative, however, we chicken out and - * use a default estimate; that probably means that one or both - * selectivities is a default estimate rather than an actual range value. + * + * If either selectivity is exactly DEFAULT_INEQ_SEL, we forget this equation + * and instead use DEFAULT_RANGE_INEQ_SEL. The same applies if the equation + * yields an impossible (negative) result. * * A free side-effect is that we can recognize redundant inequalities such * as "x < 4 AND x < 5"; only the tighter constraint will be counted. @@ -194,37 +195,51 @@ clauselist_selectivity(Query *root, if (rqlist->have_lobound && rqlist->have_hibound) { /* Successfully matched a pair of range clauses */ - Selectivity s2 = rqlist->hibound + rqlist->lobound - 1.0; - - /* Adjust for double-exclusion of NULLs */ - s2 += nulltestsel(root, IS_NULL, rqlist->var, varRelid); + Selectivity s2; /* - * A zero or slightly negative s2 should be converted into a - * small positive value; we probably are dealing with a very - * tight range and got a bogus result due to roundoff errors. - * However, if s2 is very negative, then we probably have - * default selectivity estimates on one or both sides of the - * range. In that case, insert a not-so-wildly-optimistic - * default estimate. + * Exact equality to the default value probably means the + * selectivity function punted. This is not airtight but + * should be good enough. */ - if (s2 <= 0.0) + if (rqlist->hibound == DEFAULT_INEQ_SEL || + rqlist->lobound == DEFAULT_INEQ_SEL) { - if (s2 < -0.01) - { - /* - * No data available --- use a default estimate that - * is small, but not real small. - */ - s2 = 0.005; - } - else + s2 = DEFAULT_RANGE_INEQ_SEL; + } + else + { + s2 = rqlist->hibound + rqlist->lobound - 1.0; + + /* Adjust for double-exclusion of NULLs */ + s2 += nulltestsel(root, IS_NULL, rqlist->var, varRelid); + + /* + * A zero or slightly negative s2 should be converted into a + * small positive value; we probably are dealing with a very + * tight range and got a bogus result due to roundoff errors. + * However, if s2 is very negative, then we probably have + * default selectivity estimates on one or both sides of the + * range that we failed to recognize above for some reason. + */ + if (s2 <= 0.0) { - /* - * It's just roundoff error; use a small positive - * value - */ - s2 = 1.0e-10; + if (s2 < -0.01) + { + /* + * No data available --- use a default estimate that + * is small, but not real small. + */ + s2 = DEFAULT_RANGE_INEQ_SEL; + } + else + { + /* + * It's just roundoff error; use a small positive + * value + */ + s2 = 1.0e-10; + } } } /* Merge in the selectivity of the pair of clauses */ |