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/*
Copyright (c) 2021, MariaDB Corporation.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; version 2 of the License.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1335 USA */
#include "sql_statistics.h"
/*
An equi-height histogram which stores real values for bucket bounds.
Handles @@histogram_type=JSON_HB
*/
class Histogram_json_hb : public Histogram_base
{
size_t size; /* Number of elements in the histogram */
/* Collection-time only: collected histogram in the JSON form. */
std::string json_text;
// Array of histogram bucket endpoints in KeyTupleFormat.
std::vector<std::string> histogram_bounds;
public:
static constexpr const char* JSON_NAME="histogram_hb_v1";
bool parse(MEM_ROOT *mem_root, Field *field, Histogram_type type_arg,
const char *hist_data, size_t hist_data_len) override;
void serialize(Field *field) override;
Histogram_builder *create_builder(Field *col, uint col_len,
ha_rows rows) override;
// returns number of buckets in the histogram
uint get_width() override
{
return (uint)size;
}
Histogram_type get_type() override
{
return JSON_HB;
}
/*
@brief
Legacy: this returns the size of the histogram on disk.
@detail
This is only called at collection time when json_text is non-empty.
*/
uint get_size() override
{
return json_text.size();
}
void init_for_collection(MEM_ROOT *mem_root, Histogram_type htype_arg,
ulonglong size) override;
bool is_available() override {return true; }
bool is_usable(THD *thd) override
{
return thd->variables.optimizer_use_condition_selectivity > 3 &&
is_available();
}
double point_selectivity(Field *field, key_range *endpoint,
double avg_selection) override;
double range_selectivity(Field *field, key_range *min_endp,
key_range *max_endp) override;
void set_json_text(ulonglong sz, uchar *json_text_arg)
{
size = (uint8) sz;
json_text.assign((const char*)json_text_arg,
strlen((const char*)json_text_arg));
}
private:
int find_bucket(Field *field, const uchar *lookup_val, bool equal_is_less);
};
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