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MDEV-39846 UNIQUE BLOB contains duplicate records after ALTER IGNORE with READ COMMITTED

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Force REPEATABLE READ isolation for the duration of mysql_alter_table,
so HA_CHECK_UNIQUE_AFTER_WRITE never triggers during ALTER's exclusive table copy.
(cherry-pick of 46ee272a10 - online ALTER TABLE (MDEV-32100))
This commit is contained in:
forkfun
2026-08-07 12:30:07 +02:00
parent b608e108d8
commit e4fa7ac8a2
3 changed files with 28 additions and 0 deletions
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11
mysql-test/main/long_unique_innodb.result
View File

@@ -169,4 +169,15 @@ id f
1 foo
2 foo
drop table t1;
#
# MDEV-39846 UNIQUE BLOB contains duplicate records after ALTER IGNORE with READ COMMITTED
#
create table t1 (pk int primary key, b blob) engine=innodb;
insert into t1 values (1,'foo'),(2,'foo');
set transaction isolation level read committed;
alter ignore table t1 add unique (b);
select * from t1;
pk b
1 foo
drop table t1;
# End of 10.6 tests

10
mysql-test/main/long_unique_innodb.test
View File

@@ -176,4 +176,14 @@ update ignore t1 set id = 2;
select * from t1;
drop table t1;
--echo #
--echo # MDEV-39846 UNIQUE BLOB contains duplicate records after ALTER IGNORE with READ COMMITTED
--echo #
create table t1 (pk int primary key, b blob) engine=innodb;
insert into t1 values (1,'foo'),(2,'foo');
set transaction isolation level read committed;
alter ignore table t1 add unique (b);
select * from t1;
drop table t1;
--echo # End of 10.6 tests

7
sql/sql_table.cc
View File

@@ -94,6 +94,7 @@ class Enable_wsrep_ctas_guard
#endif /* WITH_WSREP */
#include "sql_debug.h"
#include "scope.h"
#ifdef _WIN32
#include <io.h>
@@ -10647,6 +10648,12 @@ bool mysql_alter_table(THD *thd, const LEX_CSTRING *new_db,
*/
table_list->required_type= TABLE_TYPE_NORMAL;
enum_tx_isolation iso_level_initial= thd->tx_isolation;
SCOPE_EXIT([thd, iso_level_initial](){
thd->tx_isolation= iso_level_initial;
});
thd->tx_isolation= ISO_REPEATABLE_READ;
DEBUG_SYNC(thd, "alter_table_before_open_tables");
thd->open_options|= HA_OPEN_FOR_ALTER;