Locks: Pare down the traceback stored in the lock cache.

This reduces the size of the traceback data stored in the lock caches by
an order of magnitude. It is intended to help with the drastic imbalance
in lock cache network usage.

r2/r2/lib/lock.py

@@ -24,10 +24,11 @@ from __future__ import with_statement
 from time import sleep
 from datetime import datetime
 from threading import local
-from traceback import format_stack
 import os
 import socket
 
+from r2.lib.utils import simple_traceback
+
 # thread-local storage for detection of recursive locks
 locks = local()
 
@@ -58,7 +59,7 @@ class MemcacheLock(object):
     def __enter__(self):
         start = datetime.now()
 
-        my_info = (reddit_host, reddit_pid, ''.join(format_stack()))
+        my_info = (reddit_host, reddit_pid, simple_traceback())
 
         #if this thread already has this lock, move on
         if self.key in self.locks:

r2/r2/lib/utils/utils.py

@@ -20,7 +20,9 @@
 # Inc. All Rights Reserved.
 ###############################################################################
 
+import os
 import base64
+import traceback
 
 from urllib import unquote_plus
 from urllib2 import urlopen
@@ -1426,3 +1428,15 @@ def parse_http_basic(authorization_header):
     except TypeError:
         raise RequirementException
     return require_split(auth_data, 2, ":")
+
+
+def simple_traceback():
+    """Generate a pared-down traceback that's human readable but small."""
+
+    stack_trace = traceback.extract_stack(limit=7)[:-2]
+    return "\n".join(":".join((os.path.basename(filename),
+                               function_name,
+                               str(line_number),
+                              ))
+                     for filename, line_number, function_name, text
+                     in stack_trace)