unexpected result when executing DDL and DML concurrently

[killua525]

CODE master

create table t (a int, b int)
insert into t values(1,1);

connection 1

alter table t drop column b;

connection2

update t  set a=2,b=2;
update t set a=10,where b=2;
select * from t;

result
mysql> Select * from t;
+------+
| a |
+------+
| 2 |
+------+
1 row in set (0.00 sec)

[zz-jason]

Could you describe the order of executing these SQLs to help us reproduce this issue? For example, describe them in this form:

time	connection 1	connection 2
t1	xxx
t2		xxx

Also, what's the tidb version are you using?

[zz-jason]

/cc @lysu

[killua525]

Could you describe the order of executing these SQLs to help us reproduce this issue? For example, describe them in this form:

time connection 1 connection 2
t1 xxx
t2 xxx
Also, what's the tidb version are you using?

time	connection1	connection2
t1	drop column
t2	column state(write only)	update t set a =2 ,b=2
t3	column state (write only)	update t set a=20 where b=2
t4	column state (none)	select * from t

tidb3.0.5 or master
i think this issue in all version

[zimulala]

@jzdxeb
I cannot reproduce this problem with the master version. Could you describe to us the steps for reproduction? And how do you keep the TiDB on "write-only" state to execute the update statement?

[killua525]

for easy to produce this problem you can add

diff --git a/ddl/column.go b/ddl/column.go
index f38a774d5..4489e9ad1 100644
--- a/ddl/column.go
+++ b/ddl/column.go
@@ -265,6 +265,7 @@ func onDropColumn(t *meta.Meta, job *model.Job) (ver int64, _ error) {
                job.SchemaState = model.StateDeleteOnly
                colInfo.State = model.StateDeleteOnly
                ver, err = updateVersionAndTableInfo(t, job, tblInfo, originalState != colInfo.State)
+               time.Sleep(50 * time.Second)
        case model.StateDeleteOnly:
                // delete only -> reorganization
                job.SchemaState = model.StateDeleteReorganization

[zimulala]

@jzdxeb
Thank you very much for your feedback! I am working on it.