Details
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Bug
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Status: Stalled (View Workflow)
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Major
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Resolution: Unresolved
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10.1(EOL), 10.2(EOL), 10.3(EOL), 10.4(EOL), 10.5
Description
For multi equalities we try to add selectivity estimates using EITS but currently this does not work
In the function table_multi_eq_cond_selectivity
if (adjust_sel) |
{
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/* |
If ref == 0 and there are no fields in the multiple equality
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item_equal that belong to the tables joined prior to s
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then the selectivity of multiple equality will be set to 1.0.
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*/
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double eq_fld_sel= 1.0; |
fi.rewind(); |
while ((fi++)) |
{
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double curr_eq_fld_sel; |
Field *fld= fi.get_curr_field();
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if (!(fld->table->map & ~(table_bit | rem_tables))) |
continue; |
curr_eq_fld_sel= get_column_avg_frequency(fld) /
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fld->table->stat_records();
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if (curr_eq_fld_sel < 1.0) |
set_if_bigger(eq_fld_sel, curr_eq_fld_sel);
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}
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sel*= eq_fld_sel;
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}
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So as we see here the comparision
if (curr_eq_fld_sel < 1.0) |
set_if_bigger(eq_fld_sel, curr_eq_fld_sel);
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eq_fld_sel is set to 1, so eq_fld_sel would always remain 1 as we try to update the value in the cases curr_eq_fld_sel < 1.
This needs to be corrected.
What I understand the code it does here is it takes the highest selectivity estimate for fields inside the multiple equality which makes sense as
we want to keep our estimates pessimistic
After discussing with Igor he mentioned that the intention for the function was to take into account selectivity of equalities for condition on the same table like tbl.col1 = tbl.col2 .
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- Stalled
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