Consultor Eletrônico

Status: Verified

SYMPTOM(s):

Clients occasionally pause for short periods of time when connected to a very large active database

UNIX sync command causes a pause at time of checkpoint

FACT(s) (Environment):

UNIX
Progress 9.x

CAUSE:

At the time of triggering a bi checkpoint the bi mechanism must go through all modified database blocks found in the full bi clusters and place them onto the checkpoint queue.

Also, after the checkpoint it will issue a UNIX SYNC to tell the operating system to flush all modified O/S blocks from the UNIX cache. All processes writing to the O/S must wait until this has completed.

With very active databases often with large bi cluster sizes, this task can take a fair amount of time and could become quite noticeable to the clients.

FIX:

Tune the UNIX sync command. The sync command usually runs every 30/60 seconds and you may need to run it more often to spread the I/O load.

You need to consult with your Operating System vendor on how to do this. One possibility is to have a shell script running in the background, which does something similar to this:

while:
do
sleep 1
sync
Done

This causes frequent flushes of the file system caches. The sync() calls issued by the storage manager therefore take less time.