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MDEV-26750: Estimation for filtered rows is far off with JSON_HB histogram

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Fix a bug in position_in_interval(). Do not overwrite one interval endpoint
with another.
This commit is contained in:
Sergei Petrunia
2021-10-18 16:31:18 +03:00
parent 27539cd2c8
commit f3f78bed85
3 changed files with 61 additions and 9 deletions
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25
sql/opt_histogram_json.cc
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@@ -569,21 +569,34 @@ double position_in_interval(Field *field, const uchar *key, uint key_len,
if (field->pos_through_val_str())
{
StringBuffer<64> buf1, buf2, buf3;
String empty_buf1, empty_buf2, empty_buf3;
store_key_image_to_rec_no_null(field, left.data(), left.size());
String *min_str= field->val_str(&buf1, &empty_buf1);
String *min_str= field->val_str(&buf1);
/*
Make sure we've saved a copy of the data, not a pointer into the
field->ptr. We will overwrite the contents of field->ptr with the next
store_key_image_to_rec_no_null call
*/
if (&buf1 != min_str)
buf1.copy(*min_str);
else
buf1.copy();
store_key_image_to_rec_no_null(field, right.data(), right.size());
String *max_str= field->val_str(&buf2, &empty_buf2);
String *max_str= field->val_str(&buf2);
/* Same as above */
if (&buf2 != max_str)
buf2.copy(*max_str);
else
buf2.copy();
store_key_image_to_rec_no_null(field, (const char*)key, key_len);
String *midp_str= field->val_str(&buf3, &empty_buf3);
String *midp_str= field->val_str(&buf3);
res= pos_in_interval_for_string(field->charset(),
(const uchar*)midp_str->ptr(), midp_str->length(),
(const uchar*)min_str->ptr(), min_str->length(),
(const uchar*)max_str->ptr(), max_str->length());
(const uchar*)buf1.ptr(), buf1.length(),
(const uchar*)buf2.ptr(), buf2.length());
}
else
{