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opt_histogram_json.h
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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" struct Histogram_bucket { // The left endpoint in KeyTupleFormat. The endpoint is inclusive, this // value is in this bucket. std::string start_value; // Cumulative fraction: The fraction of table rows that fall into this // and preceding buckets. double cum_fract; // Number of distinct values in the bucket. longlong ndv; }; /* An equi-height histogram which stores real values for bucket bounds. Handles @@histogram_type=JSON_HB Histogram format in JSON: { // The next three are saved but not currently analyzed: "target_histogram_size": nnn, "collected_at": "(date and time)", "collected_by": "(server version)", "histogram_hb": [ { "start": "value", "size":nnn.nn, "ndv": nnn }, ... // Optionally, start and/or end can be replaced with _hex variant { "start_hex: "value", "size":nnn.nn, "ndv":nnn}, ... { "start": "value", "size":nnn.nn, "ndv": nnn, "end": "value"}, ] } Histogram is a JSON object. It has some global properties and "histogram_hb" member whose value is a JSON array of histogram buckets. Each bucket is an object with these members: "start" - the first value in the bucket. "size" - fraction of table rows that is contained in the bucket. "ndv" - Number of Distinct Values in the bucket. "end" - Optionally, the last value in the bucket. A bucket is a single-point bucket if it has ndv=1. Most buckets have no "end" member: the bucket is assumed to contain all values up to the "start" of the next bucket. The exception is single-point buckets where last value is the same as the first value. start/end can be replaced with start_hex/end_hex. In _hex variant, the constant is encoded in hex. This encoding is used to handle so called "unassigned characters": some non-UTF8 charsets have byte combinations that are not mapped to any UTF8 character. */ class Histogram_json_hb final : 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; std::vector<Histogram_bucket> buckets; std::string last_bucket_end_endp; public: static constexpr const char* JSON_NAME="histogram_hb"; bool parse(MEM_ROOT *mem_root, const char *db_name, const char *table_name, Field *field, 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 This used to be the size of the histogram on disk, which was redundant (one can check the size directly). Return the number of buckets instead. */ uint get_size() override { return (uint)size; } void init_for_collection(MEM_ROOT *mem_root, Histogram_type htype_arg, ulonglong size) override; double point_selectivity(Field *field, key_range *endpoint, double avg_sel) override; double range_selectivity(Field *field, key_range *min_endp, key_range *max_endp, double avg_sel) override; const std::vector<Histogram_bucket>& get_json_histogram() const { return buckets; } const std::string& get_last_bucket_end_endp() const { return last_bucket_end_endp; } void set_json_text(ulonglong sz, const char *json_text_arg, size_t json_text_len) { size= (size_t) sz; json_text.assign(json_text_arg, json_text_len); } private: int parse_bucket(json_engine_t *je, Field *field, double *cumulative_size, bool *assigned_last_end, const char **err); double get_left_fract(int idx); std::string& get_end_value(int idx); int find_bucket(const Field *field, const uchar *lookup_val, int *cmp); };