PC Gen: Using the DEC Redirector Slows Mail (131914)

SYMPTOMS

When you use the DEC redirector to connect to a Pathworks server that has the version 3.2 or 3.2a Microsoft Mail for PC Networks database, and the mail message file (MMF) is stored on the server, Microsoft Mail for Windows runs extremely slowly when you send or receive messages.

CAUSE

Mail accesses the MMF by using byte range locking, so to send or receive a message, it attempts to lock a byte range on the MMF, even if it already has a lock on that byte range. The Pathworks server handles multiple byte range locks on the same range as a file lock violation, even when the lock comes from the same workstation. When the server rejects the lock, the redirector attempts three more times to establish the lock, and succeeds on the last attempt. This creates a delay while Mail waits for the redirector to establish the lock.

The Pathworks server also adds to the delay by increasing the response delay when multiple file lock violations occurs on a file. Between the redirector trying four times and the server waiting longer and longer between these attempts to respond to the workstation, Mail effectively stops running for 4 to 10 seconds per message.

RESOLUTION

This is not a problem with Mail but with the underlying network architecture.

The resolution can be one of the following:

Move the MMF files to the local workstation.
Upgrade the Pathworks server to version 5.0, and use the DEC redirector version 5.0 in enhanced mode.
Upgrade Microsoft Windows version 3.1 to Microsoft Windows for Workgroups 3.11, and use the enhanced redirector.

MORE INFORMATION

Testing shows that the problem occurs primarily when you use Pathworks version 4.1, the DEC redirector version 4.1a, and Windows version 3.1; it can also occur when you run the DEC redirector version 5.0 in basic mode.

The following table summarizes the results of testing:

Client OS                     Redir    Mode         Server   Result
-----------------------------------------------------------------------
Windows 3.1                   4.1a     basic        4.1      failed (1)
Windows 3.1                   4.1a     enhanced     4.1      failed (1)
Windows for Workgroups 3.11   4.1a     enhanced     4.1      OK (2)
Windows 3.1                   4.1a     enhanced     NTAS 3.5 OK (3)
Windows 3.1                   5.0      enhanced     4.1      failed (1)
Windows 3.1                   5.0      basic        5.0      failed (1)
Windows 3.1                   5.0      enhanced     5.0      OK (4)
Windows for Workgroups 3.11   5.1      enhanced     5.0      OK (5)
Windows for Workgroups 3.11   5.1      enhanced     5.0      OK (5)

Notes:

(1) 4 lock violations per message
(2) file lock broken and file relocked, no violation
(3) 1 lock violation.
(4) 1 lock violation. Response from server was slow (~520 ms).
(5) No file locks were made