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MDEV-26886: Estimation for filtered rows less precise with JSON histogram

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- Make Histogram_json_hb::range_selectivity handle singleton buckets
  specially when computing selectivity of the max. endpoint bound.
  (for min. endpoint, we already do that).

- Also, fixed comments for Histogram_json_hb::find_bucket
This commit is contained in:
Sergei Petrunia
2021-11-26 20:03:08 +03:00
parent 106c785e2d
commit eb6a9ad705
4 changed files with 84 additions and 29 deletions
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25
mysql-test/main/statistics_json.result
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@ -7658,3 +7658,28 @@ test.t1 analyze status OK
ALTER TABLE t1 MODIFY f TEXT, ORDER BY pk;
INSERT INTO t1 (f) VALUES ('bar');
DROP TABLE t1;
#
# MDEV-26886: Estimation for filtered rows less precise with JSON histogram
#
create table t1 (a tinyint) as select if(seq%3,seq,0) as a from seq_1_to_100;
select count(*) from t1 where a <= 0;
count(*)
33
set histogram_type = JSON_HB, histogram_size=default;
analyze table t1 persistent for all;
Table Op Msg_type Msg_text
test.t1 analyze status Engine-independent statistics collected
test.t1 analyze status OK
analyze select * from t1 where a <= 0;
id select_type table type possible_keys key key_len ref rows r_rows filtered r_filtered Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 100 100.00 33.00 33.00 Using where
analyze select * from t1 where a < 0;
id select_type table type possible_keys key key_len ref rows r_rows filtered r_filtered Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 100 100.00 1.47 0.00 Using where
analyze select * from t1 where a > 0;
id select_type table type possible_keys key key_len ref rows r_rows filtered r_filtered Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 100 100.00 67.00 67.00 Using where
analyze select * from t1 where a >= 0;
id select_type table type possible_keys key key_len ref rows r_rows filtered r_filtered Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 100 100.00 100.00 100.00 Using where
drop table t1;