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MDEV-31631 Adding auto-increment to table with history online misbehaves

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Adding an auto_increment column online leads to an undefined behavior.
Basically any DEFAULTs that depend on a row order in the table, or on
the non-deterministic (in scope of the ALTER TABLE statement) function
is UB.

For example, NOW() is considered generally non-deterministic
(Item_func_now_utc is marked with VCOL_NON_DETERMINISTIC), but it's fixed
in scope of a single statement.

Same for any other function that depends only on the session/status vars
apart from its arguments.

Only two UB cases are known:
* adding new AUTO_INCREMENT column. Modifying the existing column may be
fine under certain circumstances, see MDEV-31058.
* adding new column with DEFAULT(nextval(...)). Modifying the existing
column is possible, since its value will be always present in the online
event, except for the NULL -> NOT NULL modification
This commit is contained in:
Nikita Malyavin
2023-07-27 15:26:32 +04:00
committed by Sergei Golubchik
parent e026a366bf
commit 44ca37ef17
5 changed files with 76 additions and 32 deletions
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17
mysql-test/main/alter_table_online_debug.result
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@ -990,23 +990,6 @@ set debug_sync= reset;
#
set @old_dbug=@@debug_dbug;
set debug_dbug="+d,rpl_report_chosen_key";
create table t (a int);
insert into t values (10),(20),(30);
set debug_sync= 'alter_table_online_downgraded signal downgraded wait_for goforit';
alter table t add pk int auto_increment primary key, algorithm=copy, lock=none;
connection con2;
set debug_sync= 'now wait_for downgraded';
delete from t where a = 20;
update t set a = a + 1 where a = 10;
set debug_sync= 'now signal goforit';
connection default;
Warnings:
Note 1105 Key chosen: -1
Note 1105 Key chosen: -1
select * from t;
a pk
11 1
30 3
#
# Add clumsy DEFAULT
#