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MDEV-19474: Histogram statistics are used even with optimizer_use_condition_selectivity=3

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The issue here was histogram statistics were being used even when
the level of optimizer_use_condition_selectivity doesn't allow
usage of statistics from histogram.

The histogram statistics are read for a table only when
optimizer_use_condition_selectivity > 3. But the TABLE structure can be
stored in the internal table cache and be reused for the next query.
So in this case the histogram statistics will be available for the next query.

The fix would be to make sure to use the histogram statistics only when
optimizer_use_condition_selectivity > 3.
This commit is contained in:
Varun Gupta
2021-02-09 20:27:21 +05:30
parent e926964cb8
commit a461e4d306
5 changed files with 111 additions and 4 deletions
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9
sql/sql_statistics.cc
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@ -3732,6 +3732,7 @@ double get_column_range_cardinality(Field *field,
if (!table->stats_is_read)
return tab_records;
THD *thd= table->in_use;
double col_nulls= tab_records * col_stats->get_nulls_ratio();
double col_non_nulls= tab_records - col_nulls;
@ -3762,7 +3763,7 @@ double get_column_range_cardinality(Field *field,
col_stats->min_max_values_are_provided())
{
Histogram *hist= &col_stats->histogram;
if (hist->is_available())
if (hist->is_usable(thd))
{
store_key_image_to_rec(field, (uchar *) min_endp->key,
field->key_length());
@ -3806,10 +3807,10 @@ double get_column_range_cardinality(Field *field,
max_mp_pos= 1.0;
Histogram *hist= &col_stats->histogram;
if (!hist->is_available())
sel= (max_mp_pos - min_mp_pos);
else
if (hist->is_usable(thd))
sel= hist->range_selectivity(min_mp_pos, max_mp_pos);
else
sel= (max_mp_pos - min_mp_pos);
res= col_non_nulls * sel;
set_if_bigger(res, col_stats->get_avg_frequency());
}