We have been investigating a performance issue on our production server when under high load. 
Due to high volume of read/write operations in production environment,  a read from a shared key file becomes a bottleneck in performance which causes critical time bound processes to time out.

We have a key file REPLAY_LOCK.DDF which is a text file.
The code for reading the file looks like below.
 
OPEN (REPLAY_LOCK_CHANNEL,O,'MEM:REPLAY_LOCK.DDF'+RX_HOST)
READ (REPLAY_LOCK_CHANNEL,REPLAY_LOCK,1,WAIT=Q_WAIT)      ; Read and lock control record
INCR REPLAY_LOCK_SEQ
STORE (REPLAY_CHANNEL,REPLAY_INFO) [LOCK=STORE_IT,DUP=DUP_ERROR]
 
We have run Process Monitor (procmon) on the windows server and captured data about the dbr.exe behaviour.
The captured data indicates that a LockFile action when ‘NOT GRANTED’ is retried immediately for the first three attempts.
The fourth and subsequent attempts have a 200ms delay before being attempted.