问题
I'm using MySQLdb under Python32 on Windows 7:
Python 3.2.3 (default, Apr 11 2012, 07:12:16) [MSC v.1500 64 bit (AMD64)] on win32
>>> import MySQLdb as My
>>> My.version_info
(1, 2, 3, 'final', 0)
I'm running service which calls this many times over and over and over again:
cursor = self._connection._conn.cursor()
cursor.execute(sql)
for i in cursor.fetchall(): pass # Operation that is not important
cursor.close()
gc.collect()
return set() # Will be filled with DB data
And memory usage just goes up and up and up, I've already tried diagnosing it and end up with this:
83 23.129 MB 0.000 MB cursor = self._connection._conn.cursor()
84 23.129 MB 0.000 MB cursor.execute(sql)
85 23.137 MB 0.008 MB for i in cursor.fetchall(): pass
86 23.137 MB 0.000 MB cursor.close()
87
88 23.137 MB 0.000 MB gc.collect()
89
90 23.137 MB 0.000 MB return set()
Neither __iter__ API seems to be better:
84 23.145 MB 0.000 MB cursor.execute(sql)
85 23.145 MB 0.000 MB for i in cursor: pass
86 23.152 MB 0.008 MB cursor.close()
87
88 23.152 MB 0.000 MB gc.collect()
89
90 23.152 MB 0.000 MB return set()
And neither looping manually with fetchone():
84 23.141 MB 0.000 MB cursor.execute(sql)
85 23.141 MB 0.000 MB while True:
86 23.141 MB 0.000 MB row = cursor.fetchone()
87 23.141 MB 0.000 MB if not row:
88 23.141 MB 0.000 MB break
89 23.148 MB 0.008 MB cursor.close()
90
91 23.148 MB 0.000 MB gc.collect()
92
93 23.148 MB 0.000 MB return set()
So why is not memory cleaning back to 23.129MB (why it always uses new 8KB)? Is the cursor buggy? Am I doing something wrong?
回答1:
IIRC cursor.fetchall() builds an in-memory list of rows, and since memory allocation is costly Python tends to retains memory already allocated. Try iterating over your cursor instead, ie for row in cursor: do_something_with(row).
来源：https://stackoverflow.com/questions/19267602/mysqldb-cursor-memory-leak