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MDEV-34664: Add an option to fix InnoDB's doubling of secondary index cardinalities

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(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.
This commit is contained in:
Monty 2024-07-27 13:34:26 +03:00 committed by Sergei Petrunia
parent 3359ac09a4
commit 4bf7c966b3
10 changed files with 133 additions and 14 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
mysql-test/main/mysqld--help.result
View File

@ -719,9 +719,10 @@ The following specify which files/extra groups are read (specified before remain
costs. disable_max_seek = Disable 'max_seek optimization'
for secondary keys and slight adjustment of filter cost.
disable_forced_index_in_group_by = Disable automatic
forced index in GROUP BY. This variable will be deleted
in MariaDB 11.0 as it is not needed with the new 11.0
optimizer.
forced index in GROUP BY. fix_innodb_cardinality =
Disable doubling of the Cardinality for InnoDB secondary
keys. This variable will be deleted in MariaDB 11.0 as it
is not needed with the new 11.0 optimizer.
Use 'ALL' to set all combinations.
--optimizer-max-sel-arg-weight=#
The maximum weight of the SEL_ARG graph. Set to 0 for no

63
mysql-test/main/secondary_key_costs.result
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@ -115,3 +115,66 @@ b sum(d)
6 125005000
8 125015000
drop table t1;
#
# MDEV-34664: fix_innodb_cardinality
#
set @save_userstat=@@global.userstat;
set @save_ispsp=@@global.innodb_stats_persistent_sample_pages;
set @@global.innodb_stats_persistent_sample_pages=20;
set @@global.userstat=on;
set use_stat_tables=PREFERABLY_FOR_QUERIES;
create or replace table t1 (a int primary key, b int, c int, d int, key(b,c,d)) engine=innodb;
insert into t1 select seq,seq/100,seq/60,seq/10 from seq_1_to_1000;
create or replace table t2 (a int);
insert into t2 values (1),(2),(3);
analyze table t1;
Table Op Msg_type Msg_text
test.t1 analyze status OK
select count(distinct b),count(distinct b,c), count(distinct b,c,d) from t1;
count(distinct b) count(distinct b,c) count(distinct b,c,d)
11 25 125
show index from t1;
Table Non_unique Key_name Seq_in_index Column_name Collation Cardinality Sub_part Packed Null Index_type Comment Index_comment Ignored
t1 0 PRIMARY 1 a A 1000 NULL NULL BTREE NO
t1 1 b 1 b A 22 NULL NULL YES BTREE NO
t1 1 b 2 c A 50 NULL NULL YES BTREE NO
t1 1 b 3 d A 250 NULL NULL YES BTREE NO
explain select * from t1,t2 where t1.b=t2.a;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t2 ALL NULL NULL NULL NULL 3 Using where
1 SIMPLE t1 ref b b 5 test.t2.a 45 Using index
set @@optimizer_adjust_secondary_key_costs=8;
explain select * from t1,t2 where t1.b=t2.a;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t2 ALL NULL NULL NULL NULL 3 Using where
1 SIMPLE t1 ref b b 5 test.t2.a 45 Using index
show index from t1;
Table Non_unique Key_name Seq_in_index Column_name Collation Cardinality Sub_part Packed Null Index_type Comment Index_comment Ignored
t1 0 PRIMARY 1 a A 1000 NULL NULL BTREE NO
t1 1 b 1 b A 11 NULL NULL YES BTREE NO
t1 1 b 2 c A 25 NULL NULL YES BTREE NO
t1 1 b 3 d A 125 NULL NULL YES BTREE NO
flush tables;
explain select * from t1,t2 where t1.b=t2.a;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t2 ALL NULL NULL NULL NULL 3 Using where
1 SIMPLE t1 ref b b 5 test.t2.a 90 Using index
show index from t1;
Table Non_unique Key_name Seq_in_index Column_name Collation Cardinality Sub_part Packed Null Index_type Comment Index_comment Ignored
t1 0 PRIMARY 1 a A 1000 NULL NULL BTREE NO
t1 1 b 1 b A 11 NULL NULL YES BTREE NO
t1 1 b 2 c A 25 NULL NULL YES BTREE NO
t1 1 b 3 d A 125 NULL NULL YES BTREE NO
connect user2, localhost, root,,;
show index from t1;
Table Non_unique Key_name Seq_in_index Column_name Collation Cardinality Sub_part Packed Null Index_type Comment Index_comment Ignored
t1 0 PRIMARY 1 a A 1000 NULL NULL BTREE NO
t1 1 b 1 b A 22 NULL NULL YES BTREE NO
t1 1 b 2 c A 50 NULL NULL YES BTREE NO
t1 1 b 3 d A 250 NULL NULL YES BTREE NO
connection default;
disconnect user2;
drop table t1,t2;
set global userstat=@save_userstat;
set global innodb_stats_persistent_sample_pages=@save_ispsp;
set @@optimizer_adjust_secondary_key_costs=default;

38
mysql-test/main/secondary_key_costs.test
View File

@ -1,6 +1,8 @@
--source include/have_sequence.inc
--source include/not_embedded.inc
--source include/have_innodb.inc
# Testcase for MDEV-33306 takes ~6 minutes with valgrind:
--source include/not_valgrind.inc
#
# Show the costs for rowid filter
@ -72,3 +74,39 @@ set @@optimizer_adjust_secondary_key_costs="disable_forced_index_in_group_by";
explain select b, sum(d) from t1 where c=0 group by b;
select b, sum(d) from t1 where c=0 group by b;
drop table t1;
--echo #
--echo # MDEV-34664: fix_innodb_cardinality
--echo #
set @save_userstat=@@global.userstat;
set @save_ispsp=@@global.innodb_stats_persistent_sample_pages;
set @@global.innodb_stats_persistent_sample_pages=20;
set @@global.userstat=on;
set use_stat_tables=PREFERABLY_FOR_QUERIES;
create or replace table t1 (a int primary key, b int, c int, d int, key(b,c,d)) engine=innodb;
insert into t1 select seq,seq/100,seq/60,seq/10 from seq_1_to_1000;
create or replace table t2 (a int);
insert into t2 values (1),(2),(3);
analyze table t1;
select count(distinct b),count(distinct b,c), count(distinct b,c,d) from t1;
show index from t1;
explain select * from t1,t2 where t1.b=t2.a;
set @@optimizer_adjust_secondary_key_costs=8;
explain select * from t1,t2 where t1.b=t2.a;
show index from t1;
# Flush tables or show index is needed to refresh the data in table share
flush tables;
explain select * from t1,t2 where t1.b=t2.a;
show index from t1;
# Check that the option does not affect other usage
connect (user2, localhost, root,,);
show index from t1;
connection default;
disconnect user2;
drop table t1,t2;
set global userstat=@save_userstat;
set global innodb_stats_persistent_sample_pages=@save_ispsp;
set @@optimizer_adjust_secondary_key_costs=default;

4
mysql-test/suite/sys_vars/r/sysvars_server_embedded.result
View File

@ -2275,11 +2275,11 @@ COMMAND_LINE_ARGUMENT REQUIRED
VARIABLE_NAME OPTIMIZER_ADJUST_SECONDARY_KEY_COSTS
VARIABLE_SCOPE SESSION
VARIABLE_TYPE SET
VARIABLE_COMMENT A bit field with the following values: adjust_secondary_key_cost = Update secondary key costs for ranges to be at least 5x of clustered primary key costs. disable_max_seek = Disable 'max_seek optimization' for secondary keys and slight adjustment of filter cost. disable_forced_index_in_group_by = Disable automatic forced index in GROUP BY. This variable will be deleted in MariaDB 11.0 as it is not needed with the new 11.0 optimizer.
VARIABLE_COMMENT A bit field with the following values: adjust_secondary_key_cost = Update secondary key costs for ranges to be at least 5x of clustered primary key costs. disable_max_seek = Disable 'max_seek optimization' for secondary keys and slight adjustment of filter cost. disable_forced_index_in_group_by = Disable automatic forced index in GROUP BY. fix_innodb_cardinality = Disable doubling of the Cardinality for InnoDB secondary keys. This variable will be deleted in MariaDB 11.0 as it is not needed with the new 11.0 optimizer.
NUMERIC_MIN_VALUE NULL
NUMERIC_MAX_VALUE NULL
NUMERIC_BLOCK_SIZE NULL
ENUM_VALUE_LIST adjust_secondary_key_cost,disable_max_seek,disable_forced_index_in_group_by
ENUM_VALUE_LIST adjust_secondary_key_cost,disable_max_seek,disable_forced_index_in_group_by,fix_innodb_cardinality
READ_ONLY NO
COMMAND_LINE_ARGUMENT REQUIRED
VARIABLE_NAME OPTIMIZER_MAX_SEL_ARGS

4
mysql-test/suite/sys_vars/r/sysvars_server_notembedded.result
View File

@ -2435,11 +2435,11 @@ COMMAND_LINE_ARGUMENT REQUIRED
VARIABLE_NAME OPTIMIZER_ADJUST_SECONDARY_KEY_COSTS
VARIABLE_SCOPE SESSION
VARIABLE_TYPE SET
VARIABLE_COMMENT A bit field with the following values: adjust_secondary_key_cost = Update secondary key costs for ranges to be at least 5x of clustered primary key costs. disable_max_seek = Disable 'max_seek optimization' for secondary keys and slight adjustment of filter cost. disable_forced_index_in_group_by = Disable automatic forced index in GROUP BY. This variable will be deleted in MariaDB 11.0 as it is not needed with the new 11.0 optimizer.
VARIABLE_COMMENT A bit field with the following values: adjust_secondary_key_cost = Update secondary key costs for ranges to be at least 5x of clustered primary key costs. disable_max_seek = Disable 'max_seek optimization' for secondary keys and slight adjustment of filter cost. disable_forced_index_in_group_by = Disable automatic forced index in GROUP BY. fix_innodb_cardinality = Disable doubling of the Cardinality for InnoDB secondary keys. This variable will be deleted in MariaDB 11.0 as it is not needed with the new 11.0 optimizer.
NUMERIC_MIN_VALUE NULL
NUMERIC_MAX_VALUE NULL
NUMERIC_BLOCK_SIZE NULL
ENUM_VALUE_LIST adjust_secondary_key_cost,disable_max_seek,disable_forced_index_in_group_by
ENUM_VALUE_LIST adjust_secondary_key_cost,disable_max_seek,disable_forced_index_in_group_by,fix_innodb_cardinality
READ_ONLY NO
COMMAND_LINE_ARGUMENT REQUIRED
VARIABLE_NAME OPTIMIZER_MAX_SEL_ARGS

11
sql/sql_class.cc
View File

@ -5374,6 +5374,17 @@ extern "C" int thd_current_status(MYSQL_THD thd)
}
extern "C" int thd_double_innodb_cardinality(MYSQL_THD thd)
{
/*
The original behavior was to double the cardinality.
OPTIMIZER_FIX_INNODB_CARDINALITY means do not double.
*/
return !(thd->variables.optimizer_adjust_secondary_key_costs &
OPTIMIZER_FIX_INNODB_CARDINALITY);
}
extern "C" enum enum_server_command thd_current_command(MYSQL_THD thd)
{
return thd->get_command();

1
sql/sql_class.h
View File

@ -214,6 +214,7 @@ extern "C" const char *thd_client_ip(MYSQL_THD thd);
extern "C" LEX_CSTRING *thd_current_db(MYSQL_THD thd);
extern "C" int thd_current_status(MYSQL_THD thd);
extern "C" enum enum_server_command thd_current_command(MYSQL_THD thd);
extern "C" int thd_double_innodb_cardinality(MYSQL_THD thd);
/**
@class CSET_STRING

1
sql/sql_priv.h
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@ -274,6 +274,7 @@
#define OPTIMIZER_ADJ_SEC_KEY_COST (1)
#define OPTIMIZER_ADJ_DISABLE_MAX_SEEKS (2)
#define OPTIMIZER_ADJ_DISABLE_FORCE_INDEX_GROUP_BY (4)
#define OPTIMIZER_FIX_INNODB_CARDINALITY (8)
/*
Replication uses 8 bytes to store SQL_MODE in the binary log. The day you

15
sql/sys_vars.cc
View File

@ -2823,18 +2823,21 @@ static Sys_var_ulong Sys_optimizer_trace_max_mem_size(
*/
static const char *adjust_secondary_key_cost[]=
{
"adjust_secondary_key_cost", "disable_max_seek", "disable_forced_index_in_group_by", 0
"adjust_secondary_key_cost", "disable_max_seek", "disable_forced_index_in_group_by", "fix_innodb_cardinality",0
};
static Sys_var_set Sys_optimizer_adjust_secondary_key_costs(
"optimizer_adjust_secondary_key_costs",
"A bit field with the following values: "
"adjust_secondary_key_cost = Update secondary key costs for ranges to be at least "
"5x of clustered primary key costs. "
"disable_max_seek = Disable 'max_seek optimization' for secondary keys and slight "
"adjustment of filter cost. "
"disable_forced_index_in_group_by = Disable automatic forced index in GROUP BY. "
"adjust_secondary_key_cost = Update secondary key costs for ranges to be "
"at least 5x of clustered primary key costs. "
"disable_max_seek = Disable 'max_seek optimization' for secondary keys and "
"slight adjustment of filter cost. "
"disable_forced_index_in_group_by = Disable automatic forced index in "
"GROUP BY. "
"fix_innodb_cardinality = Disable doubling of the Cardinality for InnoDB "
"secondary keys. "
"This variable will be deleted in MariaDB 11.0 as it is not needed with the "
"new 11.0 optimizer.",
SESSION_VAR(optimizer_adjust_secondary_key_costs), CMD_LINE(REQUIRED_ARG),

3
storage/innobase/handler/ha_innodb.cc
View File

@ -15013,7 +15013,8 @@ ha_innobase::info_low(
index selectivity is 2 times better than
our estimate: */
rec_per_key_int = rec_per_key_int / 2;
rec_per_key_int /= 1
+ thd_double_innodb_cardinality(m_user_thd);
if (rec_per_key_int == 0) {
rec_per_key_int = 1;