[3.12] gh-105623 Fix performance degradation in logging RotatingFileHandler (GH-105887) (GH-121116)

The check for whether the log file is a real file is expensive on NFS
filesystems.  This commit reorders the rollover condition checking to
not do the file type check if the expected file size is less than the
rotation threshold.

(cherry picked from commit e9b4ec6)

Co-authored-by: Craig Robson <craig@zhatt.com>
Co-authored-by: Oleg Iarygin <oleg@arhadthedev.net>

Author: 3 people

Lib/logging/handlers.py

@@ -187,15 +187,15 @@ def shouldRollover(self, record):
         Basically, see if the supplied record would cause the file to exceed
         the size limit we have.
         """
-        # See bpo-45401: Never rollover anything other than regular files
-        if os.path.exists(self.baseFilename) and not os.path.isfile(self.baseFilename):
-            return False
         if self.stream is None:                 # delay was set...
             self.stream = self._open()
         if self.maxBytes > 0:                   # are we rolling over?
             msg = "%s\n" % self.format(record)
             self.stream.seek(0, 2)  #due to non-posix-compliant Windows feature
             if self.stream.tell() + len(msg) >= self.maxBytes:
+                # See bpo-45401: Never rollover anything other than regular files
+                if os.path.exists(self.baseFilename) and not os.path.isfile(self.baseFilename):
+                    return False
                 return True
         return False
 

Misc/NEWS.d/next/Library/2023-06-17-09-07-06.gh-issue-105623.5G06od.rst

@@ -0,0 +1,2 @@
+Fix performance degradation in
+:class:`logging.handlers.RotatingFileHandler`. Patch by Craig Robson.