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4bf7c966b3
(With trivial fixes by sergey@mariadb.com) Added option fix_innodb_cardinality to optimizer_adjust_secondary_key_costs Using fix_innodb_cardinality disables the 'divide by 2' of rec_per_key_int in InnoDB that in effect doubles the Cardinality for secondary keys. This has the biggest effect for indexes where a few rows has the same key value. Using this may also cause table scans for very small tables (which in some cases may be better than an index scan). The user visible effect is that 'SHOW INDEX FROM table_name' will for InnoDB show the true Cardinality (and not 2x the real value). It will also allow the optimizer to chose a better index in some cases as the division by 2 could have a bad effect for tables with 2-5 identical values per key. A few notes about using fix_innodb_cardinality: - It has direct affect for SHOW INDEX FROM table_name. SHOW INDEX will also update the statistics in table share. - The effect of fix_innodb_cardinality for query plans or EXPLAIN is only visible after first open of the table. This is why one must do a flush tables or use SHOW INDEX for the option to take effect. - Using fix_innodb_cardinality can thus affect all user in their query plans if they are using the same tables. Because of this, it is strongly recommended that one uses optimizer_adjust_secondary_key_costs=fix_innodb_cardinality mainly in configuration files to not cause issues for other users.
180 lines
6.8 KiB
Text
180 lines
6.8 KiB
Text
create table t1 (
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pk int primary key auto_increment,
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nm varchar(32),
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fl1 tinyint default 0,
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fl2 tinyint default 0,
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index idx1(nm, fl1),
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index idx2(fl2)
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) engine=myisam;
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create table name (
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pk int primary key auto_increment,
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nm bigint
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) engine=myisam;
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create table flag2 (
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pk int primary key auto_increment,
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fl2 tinyint
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) engine=myisam;
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insert into name(nm) select seq from seq_1_to_1000 order by rand(17);
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insert into flag2(fl2) select seq mod 2 from seq_1_to_1000 order by rand(19);
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insert into t1(nm,fl2)
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select nm, fl2 from name, flag2 where name.pk = flag2.pk;
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analyze table t1 persistent for all;
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Table Op Msg_type Msg_text
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test.t1 analyze status Engine-independent statistics collected
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test.t1 analyze status Table is already up to date
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set optimizer_trace="enabled=on";
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set optimizer_switch='rowid_filter=on';
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set statement optimizer_adjust_secondary_key_costs=0 for
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explain select * from t1 where nm like '500%' AND fl2 = 0;
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id select_type table type possible_keys key key_len ref rows Extra
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1 SIMPLE t1 range idx1,idx2 idx1 35 NULL 1 Using index condition; Using where
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set @trace=(select trace from information_schema.optimizer_trace);
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select json_detailed(json_extract(@trace, '$**.considered_access_paths'));
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json_detailed(json_extract(@trace, '$**.considered_access_paths'))
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[
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[
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{
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"access_type": "ref",
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"index": "idx2",
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"used_range_estimates": true,
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"rowid_filter_skipped": "worst/max seeks clipping",
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"rows": 492,
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"cost": 492.3171406,
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"chosen": true
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},
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{
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"access_type": "range",
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"resulting_rows": 0.492,
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"cost": 1.448699097,
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"chosen": true
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}
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]
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]
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The following trace should have a different rowid_filter_key cost
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set statement optimizer_adjust_secondary_key_costs=2 for
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explain select * from t1 where nm like '500%' AND fl2 = 0;
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id select_type table type possible_keys key key_len ref rows Extra
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1 SIMPLE t1 range idx1,idx2 idx1 35 NULL 1 Using index condition; Using where
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set @trace=(select trace from information_schema.optimizer_trace);
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select json_detailed(json_extract(@trace, '$**.considered_access_paths'));
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json_detailed(json_extract(@trace, '$**.considered_access_paths'))
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[
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[
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{
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"access_type": "ref",
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"index": "idx2",
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"used_range_estimates": true,
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"rowid_filter_key": "idx1",
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"rows": 492,
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"cost": 3.814364688,
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"chosen": true
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},
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{
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"access_type": "range",
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"resulting_rows": 0.492,
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"cost": 1.448699097,
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"chosen": true
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}
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]
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]
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drop table t1, name, flag2;
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select @@optimizer_adjust_secondary_key_costs;
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@@optimizer_adjust_secondary_key_costs
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set @@optimizer_adjust_secondary_key_costs=7;
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select @@optimizer_adjust_secondary_key_costs;
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@@optimizer_adjust_secondary_key_costs
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adjust_secondary_key_cost,disable_max_seek,disable_forced_index_in_group_by
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set @@optimizer_adjust_secondary_key_costs=default;
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#
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# MDEV-33306 Optimizer choosing incorrect index in 10.6, 10.5 but not in 10.4
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#
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create table t1 (a int primary key, b int, c int, d int, key(b),key(c)) engine=innodb;
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insert into t1 select seq, mod(seq,10), mod(seq,2), seq from seq_1_to_50000;
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explain select b, sum(d) from t1 where c=0 group by b;
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id select_type table type possible_keys key key_len ref rows Extra
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1 SIMPLE t1 index c b 5 NULL # Using where
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select b, sum(d) from t1 where c=0 group by b;
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b sum(d)
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0 125025000
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2 124985000
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4 124995000
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6 125005000
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8 125015000
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set @@optimizer_adjust_secondary_key_costs="disable_forced_index_in_group_by";
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explain select b, sum(d) from t1 where c=0 group by b;
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id select_type table type possible_keys key key_len ref rows Extra
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1 SIMPLE t1 ALL c NULL NULL NULL # Using where; Using temporary; Using filesort
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select b, sum(d) from t1 where c=0 group by b;
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b sum(d)
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0 125025000
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2 124985000
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4 124995000
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6 125005000
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8 125015000
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drop table t1;
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#
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# MDEV-34664: fix_innodb_cardinality
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#
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set @save_userstat=@@global.userstat;
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set @save_ispsp=@@global.innodb_stats_persistent_sample_pages;
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set @@global.innodb_stats_persistent_sample_pages=20;
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set @@global.userstat=on;
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set use_stat_tables=PREFERABLY_FOR_QUERIES;
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create or replace table t1 (a int primary key, b int, c int, d int, key(b,c,d)) engine=innodb;
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insert into t1 select seq,seq/100,seq/60,seq/10 from seq_1_to_1000;
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create or replace table t2 (a int);
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insert into t2 values (1),(2),(3);
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analyze table t1;
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Table Op Msg_type Msg_text
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test.t1 analyze status OK
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select count(distinct b),count(distinct b,c), count(distinct b,c,d) from t1;
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count(distinct b) count(distinct b,c) count(distinct b,c,d)
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11 25 125
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show index from t1;
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Table Non_unique Key_name Seq_in_index Column_name Collation Cardinality Sub_part Packed Null Index_type Comment Index_comment Ignored
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t1 0 PRIMARY 1 a A 1000 NULL NULL BTREE NO
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t1 1 b 1 b A 22 NULL NULL YES BTREE NO
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t1 1 b 2 c A 50 NULL NULL YES BTREE NO
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t1 1 b 3 d A 250 NULL NULL YES BTREE NO
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explain select * from t1,t2 where t1.b=t2.a;
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id select_type table type possible_keys key key_len ref rows Extra
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1 SIMPLE t2 ALL NULL NULL NULL NULL 3 Using where
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1 SIMPLE t1 ref b b 5 test.t2.a 45 Using index
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set @@optimizer_adjust_secondary_key_costs=8;
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explain select * from t1,t2 where t1.b=t2.a;
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id select_type table type possible_keys key key_len ref rows Extra
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1 SIMPLE t2 ALL NULL NULL NULL NULL 3 Using where
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1 SIMPLE t1 ref b b 5 test.t2.a 45 Using index
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show index from t1;
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Table Non_unique Key_name Seq_in_index Column_name Collation Cardinality Sub_part Packed Null Index_type Comment Index_comment Ignored
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t1 0 PRIMARY 1 a A 1000 NULL NULL BTREE NO
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t1 1 b 1 b A 11 NULL NULL YES BTREE NO
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t1 1 b 2 c A 25 NULL NULL YES BTREE NO
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t1 1 b 3 d A 125 NULL NULL YES BTREE NO
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flush tables;
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explain select * from t1,t2 where t1.b=t2.a;
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id select_type table type possible_keys key key_len ref rows Extra
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1 SIMPLE t2 ALL NULL NULL NULL NULL 3 Using where
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1 SIMPLE t1 ref b b 5 test.t2.a 90 Using index
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show index from t1;
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Table Non_unique Key_name Seq_in_index Column_name Collation Cardinality Sub_part Packed Null Index_type Comment Index_comment Ignored
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t1 0 PRIMARY 1 a A 1000 NULL NULL BTREE NO
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t1 1 b 1 b A 11 NULL NULL YES BTREE NO
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t1 1 b 2 c A 25 NULL NULL YES BTREE NO
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t1 1 b 3 d A 125 NULL NULL YES BTREE NO
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connect user2, localhost, root,,;
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show index from t1;
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Table Non_unique Key_name Seq_in_index Column_name Collation Cardinality Sub_part Packed Null Index_type Comment Index_comment Ignored
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t1 0 PRIMARY 1 a A 1000 NULL NULL BTREE NO
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t1 1 b 1 b A 22 NULL NULL YES BTREE NO
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t1 1 b 2 c A 50 NULL NULL YES BTREE NO
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t1 1 b 3 d A 250 NULL NULL YES BTREE NO
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connection default;
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disconnect user2;
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drop table t1,t2;
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set global userstat=@save_userstat;
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set global innodb_stats_persistent_sample_pages=@save_ispsp;
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set @@optimizer_adjust_secondary_key_costs=default;
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