A quick and easy performance improvement

Richard Lynch rich at mail.wvnet.edu
Wed Jul 26 14:30:42 IST 2006

I thought I'd post to the list about a change I made yesterday which 
provided a huge boost in system's performance.

By far the largest amount of time spent in the life of a disk I/O 
operation is seek time.  Seek time is the amount of time it takes to 
move the disk R/W heads from one cylinder to another.  The /var/spool 
filesystem is where the inbound and outbound mail queues are located.  
Note also that the Bayes database is accessed heavily when analyzing a 

Like many installations we have our root filesystem (/) and /var 
filesystem on separate partitions on a single hard drive.  The default 
location for the SpamAssassin bayes database is in /root/.spamassassin/ 
which is on the rootfs.   Moving the bayes database to 
/var/spool/spamassassin resulted in a huge decrease in IOWait time.  In 
our case it was an order of magnitude reduction.  For example,  IOWait 
percentages went from 30% to 3%.  IOWait is the percentage of time the 
processor is waiting on an I/O operation to complete.  Our mail queues 
no longer get behind and throughput is outstanding! 

Making the change is trivial (from root)....

1. Shutdown MS
2. mkdir /var/spool/spamassassin
3. mv .spamassassin/bayes* /var/spool/spamassassin/
4. Edit /etc/MailScanner/spam.assassin.prefs.conf and uncomment the
    lines which define where the bayes DB is located.  Thanks Julian!  
The lines

    auto_whitelist_path        /var/spool/spamassassin/auto-whitelist
    auto_whitelist_file_mode   0600
    bayes_path                 /var/spool/spamassassin/bayes
    bayes_file_mode            0600

5. Start MS

Just wanted to let others know and perhaps benefit from our experiences.

Richard Lynch


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