Backport of revno: 2617.71.1

Bug#42546 Backup: RESTORE fails, thinking it finds an existing table

The problem occured when a MDL locking conflict happened for a non-existent 
table between a CREATE and a INSERT statement. The code for CREATE 
interpreted this lock conflict to mean that the table existed, 
which meant that the statement failed when it should not have.
The problem could occur for CREATE TABLE, CREATE TABLE LIKE and
ALTER TABLE RENAME.

This patch fixes the problem for CREATE TABLE and CREATE TABLE LIKE.
It is based on code backported from the mysql-6.1-fk tree written
by Dmitry Lenev. CREATE now uses normal open_and_lock_tables() code 
to acquire exclusive locks. This means that for the test case in the bug 
description, CREATE will wait until INSERT completes so that it can 
get the exclusive lock. This resolves the reported bug.

The patch also prohibits CREATE TABLE and CREATE TABLE LIKE under 
LOCK TABLES. Note that this is an incompatible change and must 
be reflected in the documentation. Affected test cases have been
updated.

mdl_sync.test contains tests for CREATE TABLE and CREATE TABLE LIKE.

Fixing the issue for ALTER TABLE RENAME is beyond the scope of this
patch. ALTER TABLE cannot be prohibited from working under LOCK TABLES
as this could seriously impact customers and a proper fix would require
a significant rewrite.

1 files changed, 60 insertions, 0 deletions

diff --git a/mysql-test/r/mdl_sync.result b/mysql-test/r/mdl_sync.result
index d409157a70b..e5447c32b7d 100644
--- a/mysql-test/r/mdl_sync.result
+++ b/mysql-test/r/mdl_sync.result
@@ -63,6 +63,66 @@ unlock tables;
 # Clean-up.
 drop tables t1, t2, t3, t5;
 #
+# Bug#42546 - Backup: RESTORE fails, thinking it finds an existing table
+#
+DROP TABLE IF EXISTS t1;
+set @save_log_output=@@global.log_output;
+set global log_output=file;
+#
+# Test 1: CREATE TABLE
+#
+# Connection 2 
+# Start insert on the not-yet existing table
+# Wait after taking the MDL lock
+SET DEBUG_SYNC= 'after_open_table_mdl_shared SIGNAL locked WAIT_FOR finish';
+INSERT INTO t1 VALUES(1,"def");
+# Connection 1
+SET DEBUG_SYNC= 'now WAIT_FOR locked';
+# Now INSERT has a MDL on the non-existent table t1.
+#
+# Continue the INSERT once CREATE waits for exclusive lock
+SET DEBUG_SYNC= 'mdl_acquire_exclusive_locks_wait SIGNAL finish';
+# Try to create that table.
+CREATE TABLE t1 (c1 INT, c2 VARCHAR(100), KEY(c1));
+# Connection 2
+# Insert fails
+ERROR 42S02: Table 'test.t1' doesn't exist
+# Connection 1
+SET DEBUG_SYNC= 'RESET';
+SHOW TABLES;
+Tables_in_test
+t1
+DROP TABLE IF EXISTS t1;
+#
+# Test 2: CREATE TABLE LIKE
+#
+CREATE TABLE t2 (c1 INT, c2 VARCHAR(100), KEY(c1));
+# Connection 2 
+# Start insert on the not-yet existing table
+# Wait after taking the MDL
+SET DEBUG_SYNC= 'after_open_table_mdl_shared SIGNAL locked WAIT_FOR finish';
+INSERT INTO t1 VALUES(1,"def");
+# Connection 1
+SET DEBUG_SYNC= 'now WAIT_FOR locked';
+# Now INSERT has a MDL on the non-existent table t1.
+#
+# Continue the INSERT once CREATE waits for exclusive lock
+SET DEBUG_SYNC= 'mdl_acquire_exclusive_locks_wait SIGNAL finish';
+# Try to create that table.
+CREATE TABLE t1 LIKE t2;
+# Connection 2
+# Insert fails
+ERROR 42S02: Table 'test.t1' doesn't exist
+# Connection 1
+SET DEBUG_SYNC= 'RESET';
+SHOW TABLES;
+Tables_in_test
+t1
+t2
+DROP TABLE t2;
+DROP TABLE IF EXISTS t1;
+set global log_output=@save_log_output;
+#
 # Bug #46044 "MDL deadlock on LOCK TABLE + CREATE TABLE HIGH_PRIORITY
 #             FOR UPDATE"
 #