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Code Issues

Reworked my yesterday's commit re. empty tables and indices

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This commit is contained in:
Dmitry Yemanov 2023-09-12 08:31:59 +03:00
parent 252c5b2b2f
commit 022f092877
1 changed files with 13 additions and 11 deletions
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24
src/jrd/optimizer/Retrieval.cpp
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@ -898,17 +898,6 @@ void Retrieval::getInversionCandidates(InversionCandidateList& inversions,
// Add matches for this segment to the main matches list // Add matches for this segment to the main matches list
matches.join(segment.matches); matches.join(segment.matches);
// When selectivity is zero the statement is prepared on an
// empty table or the statistics aren't updated.
// For an unique index, estimate the selectivity via the stream cardinality.
// For a non-unique one, assume 1/10 of the maximum selectivity, so that
// at least some indexes could be chosen by the optimizer.
if (scratch.selectivity <= 0)
{
scratch.selectivity = (unique && cardinality > MINIMUM_CARDINALITY) ?
1 / cardinality : DEFAULT_SELECTIVITY;
}
// An equality scan for any unique index cannot retrieve more // An equality scan for any unique index cannot retrieve more
// than one row. The same is true for an equivalence scan for // than one row. The same is true for an equivalence scan for
// any primary index. // any primary index.
@ -1001,6 +990,19 @@ void Retrieval::getInversionCandidates(InversionCandidateList& inversions,
{ {
double selectivity = scratch.selectivity; double selectivity = scratch.selectivity;
// When the index selectivity is zero then the statement is prepared
// on an empty table or the statistics aren't updated. The priorly
// calculated selectivity is meaningless in this case. So instead:
// - for an unique match, estimate the selectivity via the stream cardinality;
// - for a non-unique one, assume 1/10 of the maximum selectivity, so that
// at least some indexes could be utilized by the optimizer.
if (idx->idx_selectivity <= 0)
{
selectivity = unique ?
MIN(MAXIMUM_SELECTIVITY / cardinality, DEFAULT_SELECTIVITY) :
DEFAULT_SELECTIVITY;
}
// Calculate the cost (only index pages) for this index // Calculate the cost (only index pages) for this index
auto cost = DEFAULT_INDEX_COST + selectivity * scratch.cardinality; auto cost = DEFAULT_INDEX_COST + selectivity * scratch.cardinality;