Why mysql program hangs(deadlock)? - mysql

Question

I am struggling more than one day on dealing with a mysql hangs(deadlock). In below testcase, I will try to create the database first if it doesn't exist and try to create a table if it doesn't exist too. Then I do a query on the table. Each time I execute the SQL command, I strictly close the cursor. But the program still hangs. I have found two workarounds. 1) close the connection after creating the database and create a new connection. 2) call commit() after the query.
The two workarounds works good but they make me more confused. As my understanding, it's ok to keep connection if the cursors are closed in time and commit() are called after each change. And also, there is no reason to call commit() after query.
So my two workarounds even destroyed my understanding of database operation. I do need some help to point out what's wrong with the program basically.... Just give me some light...
Thanks very much!
#!/usr/bin/python2
import MySQLdb
def NewConnectToMySQL():
conn = MySQLdb.Connect("localhost", "root", "mypassword")
return conn
def CreateDBIfNotExists(conn):
sql = "CREATE DATABASE IF NOT EXISTS testdb"
cur = conn.cursor()
cur.execute(sql)
cur.close()
conn.select_db("testdb")
conn.commit()
"""workaround-1"""
#conn.close()
#conn = NewConnectToMySQL()
#conn.select_db("testdb")
return conn
def CreateTableIfNotExists(conn):
sql = "CREATE TABLE IF NOT EXISTS mytable (id INTEGER, name TEXT)"
cur = conn.cursor()
cur.execute(sql)
cur.close()
conn.commit()
def QueryName(conn, name):
sql = "SELECT * FROM mytable WHERE name = '%s'" % name
cur = conn.cursor()
cur.execute(sql)
info = cur.fetchall()
cur.close()
"""workaround-2"""
#conn.commit()
return info
conn1 = NewConnectToMySQL()
CreateDBIfNotExists(conn1)
CreateTableIfNotExists(conn1)
QueryName(conn1, "tom")
conn2 = NewConnectToMySQL()
CreateDBIfNotExists(conn2)
CreateTableIfNotExists(conn2) #hangs here!!!!!!!!!!
Here is the output of SHOW FULL PROCESSLIST when hangs.
mysql> SHOW FULL PROCESSLIST
-> ;
+-----+------+-----------+--------+---------+------+---------------------------------+------------------------------------------------------------+
| Id | User | Host | db | Command | Time | State | Info |
+-----+------+-----------+--------+---------+------+---------------------------------+------------------------------------------------------------+
| 720 | root | localhost | testdb | Sleep | 96 | | NULL |
| 721 | root | localhost | testdb | Query | 96 | Waiting for table metadata lock | CREATE TABLE IF NOT EXISTS mytable (id INTEGER, name TEXT) |
| 727 | root | localhost | NULL | Query | 0 | NULL | SHOW FULL PROCESSLIST |
+-----+------+-----------+--------+---------+------+---------------------------------+------------------------------------------------------------+
3 rows in set (0.00 sec)