DROP VIEW IF EXISTS causes server crash (breaking mydumper)

[morgo]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. What did you do?

myloader tries to drop a table as both a view and a table when restoring with the -o option (overwrite). It crashes tidb, which I managed to reduce to this test case:

MySQL [test]> CREATE TABLE t1 (a int);
DRQuery OK, 0 rows affected (0.53 sec)

MySQL [test]> DROP VIEW IF EXISTS t1;
ERROR 2013 (HY000): Lost connection to MySQL server during query

2. What did you expect to see?

Not crash.

3. What did you see instead?

See above.

4. What version of TiDB are you using (tidb-server -V or run select tidb_version(); on TiDB)?

MySQL [test]> select tidb_version()\G
*************************** 1. row ***************************
tidb_version(): Release Version: v2.1.0-rc.3-5-g99c4a15ce
Git Commit Hash: 99c4a15ce422603a6ad02be8ace19a43f8a26162
Git Branch: newmaster
UTC Build Time: 2018-10-07 04:24:32
GoVersion: go version go1.11 linux/amd64
Race Enabled: false
TiKV Min Version: 2.1.0-alpha.1-ff3dd160846b7d1aed9079c389fc188f7f5ea13e
Check Table Before Drop: false
1 row in set (0.00 sec)

[shenli]

We will fix it soon.

[tianjiqx]

I found that this bug seems to be just a simple null pointer problem.Just modify one line to fix it.

[zz-jason]

@tianjiqx Good! Could you file a PR to fix this issue?

[tianjiqx]

@zz-jason
I checked if I should use the p.Schema() function in other places instead of using p.schema directly?
Or if there are no bugs, it will not change other places.

[zz-jason]

@tianjiqx I think we forget to set the schema for LogicalTableDual in somewhere, it's better to find out why the schema is empty. BTW, we don't need to replace all the p.schema to p.Schema().

[tianjiqx]

@zz-jason
That's right. Well, I need to continue to look at the relevant code logic.

[tianjiqx]

drop view statement as ast.DoStmt handled in buildDo,I think can set schema at here

--- a/planner/core/planbuilder.go
+++ b/planner/core/planbuilder.go
@@ -227,6 +227,8 @@ func (b *PlanBuilder) buildDo(v *ast.DoStmt) (Plan, error) {
                        RetType:  expr.GetType(),
                })
        }
+       //make dual schema if not
+       var _ = dual.Schema()
        p.SetChildren(dual)
        p.self = p
        p.SetSchema(schema)

BTW，The view function does not seem to be fully implemented yet?

mysql> CREATE VIEW v AS SELECT qty, price, qty*price AS value FROM t;
Query OK, 0 rows affected (0.00 sec)

mysql> CREATE VIEW v AS SELECT qty, price, qty*price AS value FROM t;
Query OK, 0 rows affected (0.00 sec)

mysql> CREATE VIEW v AS SELECT qty, price, qty*price AS value FROM t;
Query OK, 0 rows affected (0.00 sec)

mysql> select * from v;
ERROR 1146 (42S02): Table 'test.v' doesn't exist

mysql> drop view if exists v;
Query OK, 0 rows affected (0.00 sec)

[shenli]

@tianjiqx Actually, TiDB doesn't support View.