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MDEV-26849: JSON Histograms: point selectivity estimates are off

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.. for non-existent values.

Handle this special case.
This commit is contained in:
Sergei Petrunia
2021-10-22 19:43:19 +03:00
parent f3f78bed85
commit 05877df472
8 changed files with 142 additions and 10 deletions
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10
sql/opt_histogram_json.cc
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@@ -616,7 +616,7 @@ double position_in_interval(Field *field, const uchar *key, uint key_len,
double Histogram_json_hb::point_selectivity(Field *field, key_range *endpoint,
double avg_sel)
double avg_sel, double total_rows)
{
const uchar *key = endpoint->key;
if (field->real_maybe_null())
@@ -631,9 +631,11 @@ double Histogram_json_hb::point_selectivity(Field *field, key_range *endpoint,
if (buckets[idx].ndv == 1 && !equal)
{
// The bucket has a single value and it doesn't match! Use the global
// average.
sel= avg_sel;
/*
The bucket has a single value and it doesn't match! Return a very
small value.
*/
sel= 1.0 / total_rows;
}
else
{